Melaleuca – Tea-tree oil (Melaleucae aetheroleum)

Latin name of the genus:Melaleuca
Latin name of herbal substance:Melaleucae aetheroleum
Botanical name of plant:Melaleuca alternifolia (maiden and betche) cheel
English common name of herbal substance:Tea-tree oil
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Latin name of the genus: Melaleuca
Latin name of herbal substance: Melaleucae aetheroleum
Botanical name of plant: Melaleuca alternifolia (Maiden and Betche) Cheel, and/or other spieces of Melaleuca
English common name of herbal substance: Tea-tree oil

Melaleuca - Tea-tree oil - Melaleuca alternifolia (Maiden and Betche) Cheel, and/or other spieces of Melaleuca

Table of Contents


1. Introduction

1.1. Description of the herbal substance(s), herbal preparation(s) or combinations thereof

Herbal substance(s)

Melaleuca alternifolia tree is a member of the botanical family Myrtaceae. The name tea tree was established for the plant because the leaves were used to prepare an aromatic tea.

The term “Tea Tree” includes species of the genus Leptospermum and Melaleuca (more than 150 species) of the family Myrtaceae. The best known and economically most important species is the Australian Tea Tree (Saller et al. 1998).

Herbal preparation(s)

The preparation with pharmacological interest is the oil from the leaves (called tea tree oil, TTO), because it has been reported as having immuno-stimulatory property and activity against bacterial, viral and fungal organisms. It is also known that it can attenuate inflammation and may help wound healing (Carson et al. 2006).

There are several historical terms for TTO, including ‘‘melaleuca oil’’ and ‘‘ti tree oil’’, ‘‘ti tree’’ being a

Maori and Samoan common name for plants in the genus Cordyline. The term ‘‘Melaleuca oil’’ has been selected as the official approved name by the Therapeutic Goods Administration of Australia (Carson & Riley 2001).

About 2% essential oil can be obtained from the leaves of the Australian Tea Tree by extraction with lipophilic organic solvent or by steam distillation. According to the European Pharmacopoeia TTO is obtained by steam distillation from the foliage and terminal branchlets of Melaleuca alternifolia (Maiden and Betch) Cheel, M. linariifolia Smith, M. dissitiflora F. Mueller and/or other species of Melaleuca. It is a clear, mobile, colourless or pale yellow liquid with no visible trace of water and has a distinct pleasant odour like turpentine with a high content of terpenes (> 50 to 60%) and a specific weight of 0.89. It is almost insoluble in water, but mixes well with most organic solvents (Saller et al. 1998).

TTO is produced mainly from Melaleuca alternifolia on large-scale plantations in the states of New South Wales and Queensland in Australia. Prior to commercial cultivation, the natural habitat of Melaleuca alternifolia was limited to the area around the Clarence and Richmond Rivers in northeastern coast of New South Wales. Other Melaleuca species, including Melaleuca dissitiflora and Melaleuca linariifolia, have produced oils which meet the international standard, such as ‘‘cajuput’’ oil (also ‘‘cajeput’’ or ‘‘cajaput‘‘) from Melaleuca cajuputi and ‘‘niaouli’’ oil from Melaleuca quinquenervia

(Carson & Riley 2001).

TTO is composed of terpene hydrocarbons, mainly monoterpenes, sesquiterpenes and their associated alcohols. According to Carson et al. (2006), the early reports on the number of components TTO was put at up to 48, however in 1989 a paper was published reporting on the examination of over 800 samples of TTO and concluded that there were approximately 100 components (Brophy 1989). This wide variation and the potential for batch-to-batch variation led in 1996 to an international standard for “Oil of Melaleuca – terpinen-4-ol type (TTO)”. Prior to this there was an Australian standard. The Australian standard specified that the 1,8-cineole content of TTO must not exceed 15%, while terpinen-4-ol content must exceed 30% (Carson & Riley 2001).

The chemical composition of TTO consists largely of cyclic monoterpenes of which about 50% are oxygenated and about 50% are hydrocarbons (Cox et al. 2000).

The oil contains 42.35% terpinen-4-ol, 20.65% γ-terpinene, 9.76% α-terpinene, 3.71% terpinolene, 3.57% 1,8-cineole, 3.09%, α-terpineol, 2.82% p-cimene, 2.42% α-pinene, 1.75% limonene, 1.05% δ- cadinene, 0.94% α-thujene, 0.94% aromadendrene, 0.87% myrcene, 0.73% β-pinene, 0.40% sabinene, and 0.34% α-phellandrene (Bozzuto et al. 2011).

Since the exact composition of TTO is variable, according to the Australian and International Standards Organizations, the substance known as TTO from Melaleuca alternifolia has a chromatographic profile within given ranges (Halcón & Milkus 2004).

The European Pharmacopoeia and the International Standard ISO 4730 require TTO to have a minimum content of 30% of terpinen-4-ol and a maximum content of 15% of 1,8-cineole. Terpinen-4- ol is the major TTO component and has shown strong antimicrobial and anti-inflammatory properties (in Mondello et al. 2006), while 1,8-cineole is probably an undesirable allergen in TTO products (Carson & Riley 2001).

Table 1: Main constituents of tea tree oil

TTO is incorporated in topical formulations for the treatment of cutaneous infections (Carson et al. 2006; Hammer et al. 2006). The concentrations of TTO found in commercially available products range from 2 to 5%. Terpinen-4-ol is the main antimicrobial compound, but other components, such as α- terpineol, also have similar antimicrobial activities (Carson et al. 2006).

TTO has to be stored in air-tight containers, protected from light and heat, because proper storage and handling are needed to avoid the formation of oxidation products which have greater potential for skin sensitisation (British Pharmaceutical Codex 1949, WHO 2004). A shelf-life of 12 months after opening is recommended for formulated TTO products by the Australian Government – Rural Industries Research and Development Corporation (2007).

TTO has been used for many years as a component in cosmetic products. It has also been used as an ingredient in medicinal products for its antimicrobial properties especially in treating cutaneous infections. It has been listed in various reference books including the British Pharmaceutical Codex

1949 and books on Essential Oils (Penfold & Morrison 1950) and the World Health Organisation in 2004 has published a monograph on “Aetheroleum Melaleucae Alternifoliae”.

Combinations of herbal substance(s) and/or herbal preparation(s) including a description of vitamin(s) and/or mineral(s) as ingredients of traditional combination herbal medicinal products assessed, where applicable.

Not applicable.

1.2. nformation about products on the market in the Member States

Regulatory status overview

MA: Marketing Authorisation TRAD: Traditional Use Registration

Other TRAD: Other national Traditional systems of registration

This regulatory overview is not legally binding and does not necessarily reflect the legal status of the products in the MSs concerned.

1.3. Search and assessment methodology

This assessment report reviews the scientific literature data available for Melaleuca alternifolia essential oil, and from the WHO monograph, European Pharmacopoeia monograph, British Pharmaceutical Codex monograph, ESCOP monograph, PubMed, EMA library and the internet, as well as available information on products marketed in the European Community, including pharmaceutical forms, indications, posology and methods of administration.

The keywords “Melaleuca alternifolia”, “tea tree oil”, in all text fields were used. The information ad references provided by the Australian Tea Tree Industry (ATTIA Ltd.) following the call for submission of scientific data were also taken into consideration. Only clinical studies with tea tree oil were included in the assessment report.

2. Historical data on medicinal use

2.1. Information on period of medicinal use in the Community

Melaleuca alternifolia oil has been used as medicinal by Australian Bundjabung Aborigines for several millennia for bruises, insect bites, and skin infections. European colonists soon recognized the therapeutic properties and began to distil oil from its leaves (Carson & Riley 2001). Members of the crew of James Cook described at the end of the eighteenth century the use of the TTO. It was rediscovered in the 1920s as a topical antiseptic with more effective activity than phenol (Bozzuto et al. 2011).

The essential oil was distilled for the first time in 1925 and due to its antiseptic, antibacterial and antifungal effects became a standard antiseptic agent for surgery, especially for dental surgery (Saller et al. 1998).

The monograph on TTO of the British Pharmaceutical Codex of 1949 reports that TTO has germicidal properties and has been used as a local application in the treatment of furunculosis, tinea, paronychia,

impetigo, trush and stomatitis, and as inhalant in coryza. In veterinary practice it has been used in the treatment of mange and eczema and in sores and skin diseases of parasitic origin.

TTO has been used for its bactericidal and fungicidal properties as a disinfectant component in several medicinal combination products with non-herbal ingredients authorised in UK since before 1970.

A cutaneous liquid containing TTO has been authorised in Denmark from 1993 to 2009 for disinfection in acne and in fungal infections on the foot.

In Sweden a cutaneous liquid is marketed since 1988 and a oromucosal and cutaneous solution is registered in Hungary since 2004.

In Australia, the Complementary Medicines Evaluation Committee (CMEC) recommended in 1999 to the TGA that registration applications for uncompounded TTO products, intended for topical use and with low level claims of a first aid nature, can be approved by the TGA without requiring prior consideration and recommendation by CMEC (CMEC extracted ratified minutes).

There is a significant number of 100% TTO medicinal products authorised in Australia to date.

Table 2 shows a consistent and long standing use of TTO demonstrated for more than 30 years, since 1930, internationally and for more than 15 years, since 1933, in the European Community. A wide range of traditional indications have been described for local application including the nasal, mouth and throat regions.

TTO has been used as an antiseptic for special and general dental surgery and in denture and mouth washes (MacDonald 1930, Anonymous 1933, Penfold & Morrison 1937, Penfold & Morrison 1950). It has also been indicated for a variety of skin conditions including bacterial and fungal infections of the skin such as acne, furunculosis, dermatophytosis (tinea pedis, tinea cruris, tinea barbae), pityriasis versicolor (tinea versicolor), parionychia, impetigo, empyema, dermatitis, eczema, psoriasis, skin rashes, impetigo contagiosa, pediculosis, ringworm, thrush, infected pustules, intertrigo and nail infections (caused by Candida albicans), parasitic skin diseases (Penfold & Morrison 1937, Penfold & Morrison 1950, Humphery 1930, Martindale 1993, British Pharmaceutical Codex 1949, Walker 1972, WHO 2004, Williamson 2003, Lawless 1994, Drury 1991).

Many different foot problems have been treated by TTO including onychomycosis infections of toenails, bromidrosis, malodour, cracks, fissures, peeling, callused heels, inflammation of corns, calluses, bunions, hammertoes, post-operative wound healing (Walker 1972, WHO 2004). It has also been used for the treatment of infected, colonised, dirty wounds, diabetic gangrene and chronic leg ulcers, burns and wounds (Penfold & Morrison 1937, Penfold & Morrison 1950, Humphery 1930, WHO 2004).

Throat, nasal and mouth conditions including acute nasopharyngitis, catarrh, thrush, stomatitis, tonsillitis, mouth ulcers, sore throat, coughs and colds, nasopharyngitis, sinus congestion, tonsillitis, pyorrhoea, gingivitis are traditional indications for use of TTO (Penfold & Morrison 1937, Penfold & Morrison 1950, Humphery 1930, British Pharmaceutical Codex 1949, WHO 2004).

TTO has been used for vaginal infections and gynaecological conditions including vaginitis, cystitis and cervicitis (Penfold & Morrison 1937, Penfold & Morrison 1950, Humphery 1930, WHO 2004), irrigation of bladder and urethra (Anonymous 1933), symptomatic treatment of colitis (WHO 2004) and as an inhalant in coryza (British Pharmaceutical Codex 1949).

Table 2: Traditional use of tea tree oil

2.2. Information on traditional/current indications and specified substances/preparations

The leaves were macerated in water for a long period (hours or even days) and then used as infusion or impregnated dressing especially in treating common cold, sore throat, insect bites, wounds or fungal skin infections as well as in delousing (Saller et al. 1998).

The essential oil had been used during the Second World War as a general antimicrobial agent and insect repellent, and provided in the first aid kits of serving Australian soldiers. The essential oil is nowadays used as a strong antimicrobial and antifungal agent in creams, soaps, toothpastes and other preparations and it has been used both externally and internally by both herbalists and aromatherapists (Lis-Balchin et al. 2000).

In modern times, TTO is reputed to have several medicinal properties including antibacterial, antifungal, antiviral, anti-inflammatory and analgesic properties. For its antibacterial activity is today popular as a topical antimicrobial agent (Carson et al. 1998). It has been recommended in the treatment of many cutaneous conditions, including acne, eczema, furunculosis, onychomycosis and tinea (Carson et al. 2006).

TTO enjoys remarkable popularity as a topical antimicrobial agent and, although it is marketed mainly for its well-documented antibacterial, antifungal and antiviral properties, the oil also has anti- inflammatory, analgesic, insecticidal and antipruritic properties (Edmondson et al. 2011). Currently it is also incorporated as the principal antimicrobial or as a natural preservative in many pharmaceutical and cosmetic products intended for external use (Cox et al. 2000).

TTO has a number of characteristics which suggest potential for its use in wound treatments or protectants against fly strike. It has documented insecticidal effects, which could be of use in the treatment of larvae in strikes, and repellent effects (Callander & James 2011).

In Australia, it has also a long history of clinical use in the treatment of foot problems such as tinea pedis and toenail onychomycosis. Dermatologic studies have been conducted in the treatment of acne, dandruff, head lice, and recurrent herpes labialis, in which effects were found to be either similar or better than traditional treatment, and often with fewer side effects. A few published studies report the successful use of TTO in treating mucous membrane infections, including Trichomonas vaginalis, and against oral bacteria and oropharyngeal candidiasis (Halcón & Milkus 2004). 100% TTO is listed by the Australian Therapeutic Goods Administration. A wide range of claims for use are permitted [Quoted at Austteam Tea Tree Oil Conference, 1995].

In Denmark it has been authorised for disinfection in acne and in fungal infections on the foot (1993- 2009).

In Sweden TTO is used against itch at mild athlete´s foot, for uncomplicated insect bites and for treatment of mild acne, in Hungary for treatment of skin infection, stomatitis, gingivitis, cut wounds, excoriation and acne.

2.3. Specified strength/posology/route of administration/duration of use for relevant preparations and indications

TTO is usually topically applied at concentrations 1.0%-100% for treating microbial infections (Combest 1999).

Tea tree preparations containing 10% and 100% TTO have been used in clinical trials to treat tinea pedis and onychomycosis, respectively (Buck et al. 1994; Tong et al. 1992).

For treating athlete’s foot, it is advised to dilute the concentrated oil with an equal amount of water or vegetable oil and apply to the affected area three times a day with a cotton ball (Combest 1999).

A topically applied 5% solution appears to be effective in treating acne (Bassett et al. 1990).

Several published reports have addressed minimum inhibitory and bactericidal concentrations of TTO against clinical isolates of Staphylococcus aureus. A study of 105 clinical isolates of Staphylococcus aureus using a broth microdilution method found the MIC90 (Minimal Inhibitory Concentration required to inhibit the growth of 90% of organisms) of TTO to be 0.5%. A later study of 100 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) found the MIC90 of TTO to be 0.32% (Halcón & Milkus 2004).

In Australia, in 1995 the Medicines Evaluation Committee approved undiluted TTO as a “mild antiseptic for minor cuts, abrasions, bites and stings and minor burns”. [Quoted at Austteam Tea Tree Oil

Conference, 1995]

According to the posology of medicinal products licensed in Europe for application on the skin TTO should always be diluted before use. In Sweden it is diluted in olive oil or baby oil 1:9 and dabbed on the afflicted areas of the skin 1-3 times daily. The rate of dilution in Denmark was 1:9 as well. The use is not recommended for children under 12 years of age. In acne or athlete’s foot the maximum duration of use is 1 month of treatment.

In Hungary the daily dose for cutaneous use is 10-15 drops (corresponding to 0.33–0.5 ml or 0.3147- 0.47205 g) to be stirred in 50 ml of lukewarm water and the solution is applied on the skin with a sterile cotton wool or gauze. In case of stomatitis and gingivitis 5-10 drops (corresponding to 0.17– 0.33 ml or 0.15735-0.47205 g) to be mixed in 100 ml of water for gargle several times daily (1 ml is 30 drops and 1 g is about ~32 drops). If the symptoms do not improve after 5 days treatment the use of products should be stopped.

A number of papers, documents and letter on the sales of TTO in Europe, provided by Interested Parties, represent a body of data that, as a whole, substantiates the medicinal use of undiluted TTO in Europe for at least 15 years (Drury 1991, Drury 1995, Lawless 1994, Lawless 1996). In these papers and documents the use of undiluted TTO is specified and posology is given. In addition this was supported by wide spread evidence of use by way of magazine articles, sales figures and books.

Table 3: Information on preparations of TTO grouped according to the traditional use

* a preparation containing 40% of TTO in a soap base called Melasol in Australia and Ti.Trol solution in England (Anonimous 1933)

Long-standing use for at least 30 years, 15 of them within the European community, is therefore demonstrated for the undiluted TTO and for the following preparations and indications:

1)Liquid preparation containing 0.5% to 10% of essential oil to be applied to the affected area 1-3 times daily for treatment of small superficial wounds and insect bites. Traditional use of this preparation is substantiated by the presence in the BPC 1949, by the European market overview (in Sweden since 1988, registered in Hungary since 2004) and by the widespread use in Australia documented since 1930. For the same indication 1-2 drops (0.033-0.066 ml) of the undiluted essential oil are applied to the affected area using a cotton bud 1-3 times daily.

2)Oily liquid or semi-solid preparation, containing 10% of essential oil, to be applied to the affected area 1-3 times daily or 0.7-1 ml of essential oil stirred in 100 ml of lukewarm water to be applied as an impregnated dressing to the affected areas of the skin for treatment of small boils (furuncles and mild acne). Traditional use of this preparation is substantiated by the presence in the BPC 1949 (treatment of furunculosis), by the European market overview (in Sweden since 1988, in Denmark from 1993 to 2009) and by the widespread use in Australia. The undiluted essential oil is to be applied to the boil using a cotton bud 2-3 times daily.

3)Oily liquid or semi-solid preparation, containing 10% of essential oil, to be applied to the affected area 1-3 times daily for the relief of itching and irritation in cases of mild athlete´s foot. Traditional use of this preparation is substantiated by the European market overview (in Sweden since 1988, in Denmark from 1993 to 2009) and by the widespread use in USA, documented since 1972, and in Australia documented since 1930. For the same indication 0.17-0.33 ml of essential oil in is diluted in an appropriate volume (a bowl) of warm water to soak feet for 5-10 minutes a day. The undiluted essential oil is to be applied to the affected area using a cotton bud 2-3 times daily until the condition is cleared up.

4)0.17–0.33 ml of TTO to be mixed in 100 ml of water for rinse or gargle several times daily for symptomatic treatment of minor inflammation of oral mucosa. Traditional use of this preparation is substantiated by the presence in the BPC 1949 (stomatitis) and by the European market overview (registered in Hungary since 2004) and by the widespread use in Australia documented since 1937.

3. Non-Clinical Data

3.1. Overview of available pharmacological data regarding the herbal substance(s), herbal preparation(s) and relevant constituents thereof

Based on results of laboratory and animal studies, there are several likely mechanisms by which a topical TTO preparation may facilitate healing in chronic Staphylococcus-infected wounds. Preliminary studies suggest both reduction in microbial load and changes in immune function related to TTO applications. Terpinen-4-ol, linalool, and α-terpineol are the most studied active antibacterial components of TTO (Halcón & Milkus 2004).

3.1.1. Primary pharmacodynamics

Antibacterial activity

The oil exhibits a broad spectrum of antimicrobial activity in vitro although its efficacy in vivo remains relatively unsubstantiated. Antibacterial activity against Staphylococcus aureus, both methicillin- susceptible (MSSA) and -resistant (MRSA) has been demonstrated (Carson et al. 1996).

Minimum inhibitory concentrations (MICs) have been determined for many organisms including coagulase-negative staphylococci (0.06-3% v/v), Staphylococcus aureus (including MRSA) (0.12- 0.5%), Streptococcus spp. (0.03-0.12%), vancomycin-resistant enterococci (VRE) (0.5-1%),

Acinetobacter baumannii (0.06-1%), Escherichia coli (0.12-0.25%), Klebsiella pneumoniae (0.12- 0.5%), Candida albicans (0.12-0.25%), other Candida species (0.12-0.5%) and Malassezia furfur (0.12-0.25%). The wide range of organisms susceptible to TTO suggests that it may be useful for skin antisepsis. Furthermore, many organisms that colonise skin transiently have been shown to be more susceptible to TTO than commensal organisms (Carson et al. 1998).

MICs of TTO range from 0.06 to 0.5% (v/v) for Escherichia coli, Staphylococcus aureus and

Streptococcus spp., and 2 to 8% (v/v) for Pseudomonas aeruginosa (Longbottom et al. 2004).

A study was carried out to evaluate the activities of TTO against lactobacilli and a range of organisms associated with bacterial vaginosis. MIC data indicated that a variety of anaerobic and aerobic bacteria are susceptible to TTO. The data also show that all lactobacilli tested were appreciably more resistant to TTO than organisms known to be associated with bacterial vaginosis, with at least a twofold difference in MIC90 results. Therefore, authors suggested that previous clinical success reported by Blackwell may be due, in part, to the susceptibility of bacterial vaginosis-associated organisms to TTO and the relative resistance of commensal Lactobacillus spp. The authors suggested that this difference in susceptibility could allow formulation of products that will selectively kill or inhibit certain organisms while having a minimal effect on the commensal lactobacilli (Hammer et al. 1999).

In vitro studies established that MIC and MBC (minimum bactericidal concentration) of TTO range from 0.003 to 2% (v/v). Studies indicate that several oral bacteria are susceptible, suggesting that TTO may be used in oral healthcare products and in maintenance of oral hygiene (Hammer et al. 2003a).

TTO and α-terpineol and terpinen-4-ol shows to have antibacterial activity against growth of Staphylococcus aureus and Escherichia coli biofilms at concentration about 0.78%. Terpinen-4-ol seems to have the most potent activity (Budzyńska et al. 2011).

The in vitro activity of TTO against MRSA has been shown many times with minimum inhibitory concentrations ranging from 0.25% to 2% (Edmondson et al. 2011).

The broad-spectrum antimicrobial activity of TTO is mainly attributed to terpinen-4-ol and 1,8-cineole, major components of the oil, and includes antibacterial, antifungal, antiviral, antiprotozoal and antimycoplasmal activities, all promoting TTO as therapeutic agent (Furneri et al. 2006, Carson et al. 2006).

McMahon et al. (2007) has suggested that the treatment of both Gram-positive and Gram-negative bacteria with low levels of TTO results in organisms becoming less susceptible to antibiotics when compared to cells not treated with TTO. One interpretation of these data is that cells undergo an adaptive response that produced cross-tolerance to conventional antimicrobial agents in addition to potentially protecting cells from TTO.

The effect of sub-lethal challenge with TTO on the antibiotic resistance profiles of staphylococci has been studied. Isolates of MRSA and MSSA and coagulase-negative staphylococci (CoNS) were habituated to sub-lethal concentrations of TTO (72 h). Following habituation, the minimum inhibitory concentrations (MIC) of antibiotics and TTO were determined. Habituated MRSA⁄MSSA cultures had higher (P < 0.05) MIC values than control cultures for the examined antibiotics. Habituated

MRSA⁄MSSA cultures also displayed decreased susceptibility to TTO. Conclusions of the authors were that TTO habituation ‘stress-hardens’ MRSA and MSSA was evidenced by transient decreased antibiotic susceptibility and stable decreased TTO susceptibility. Although TTO habituation did not decrease susceptibility of CoNS to TTO, such cultures showed transient decreased antibiotic susceptibility.

Results suggested that application of TTO at sub-lethal concentrations may reduce the efficacy of topical antibiotics used with TTO in combination therapies (McMahon et al. 2008).

Carson (2009), Thomsen et al. (2009) and Hammer & Riley (2009) attempted to reproduce the results of McMahon et al. (2007), but were unsuccessful. The authors have suggested that exposure to sub- inhibitory concentrations of TTO does not appear to affect the susceptibility or resistance to conventional antibiotics.

Carson et al. (2002) investigated the mechanisms of action of TTO and three of its components, 1,8- cineole, terpinen-4-ol, and α-terpineol, against Staphylococcus aureus ATCC 9144. They reported that treatment with the test compounds at the MIC and two times the MIC, reduced the viability of Staphylococcus aureus, particularly the treatment with terpinen-4-ol and α –terpineol. None of the compounds caused lysis, as determined by measurement of the optical density at 620 nm, although cells became disproportionately sensitive to subsequent autolysis. Staphylococcus aureus organisms treated with TTO or its components at the MIC or two times the MIC showed a significant loss of tolerance to NaCl.

When the compounds were tested at one-half the MIC, only 1,8-cineole significantly reduced the tolerance of Staphylococcus aureus to NaCl. Electron microscopy of terpinen-4-ol-treated cells showed the formation of mesosomes and the loss of cytoplasmic contents. The authors concluded that the predisposition to lysis, the loss of 260-nm-absorbing material, the loss of tolerance to NaCl, and the altered morphology seen by electron microscopy all suggest that TTO and its components compromise the cytoplasmic membrane.

Antiviral activity

In their review paper Carson et al. (1996) stated that the antiviral activity of TTO was first shown using tobacco mosaic virus and tobacco plants. In field trials TTO (spray concentration 0, 100, 250 or 500 ppm) was sprayed on plants that were then experimentally infected with tobacco mosaic virus. After 10 days, there were significantly fewer lesions per square centimetre of leaf in plants treated with TTO than in controls.

Another study has been conducted in 2001 by Schnitzler et al. with herpes simplex viruses that were incubated with various concentrations of TTO; these treated viruses were then used to infect cell mono-layers. After 4 days, the numbers of plaques formed by TTO-treated virus and untreated control virus were determined and compared. The concentration of TTO inhibiting 50% of plaque formation was 0.0009% for herpes simplex virus type 1 and 0.0008% for herpes simplex virus type 2, relative to controls. These studies also showed that at the higher concentration of 0.003%, TTO reduced herpes simplex virus-1 titres by 98.2% and HSV-2 titres by 93.0%. In addition, by applying TTO at different stages in the virus replicative cycle, TTO was shown to have the greatest effect on free virus (prior to infection of cells). Another study evaluated the activities of 12 essential oils, including TTO, for activity against herpes simplex virus -1 in Vero cells. Again, TTO was found to exert most of its antiviral activity on free virus, with 1% oil inhibiting plaque formation completely and 0.1% TTO reducing plaque formation by approximately 10%. Pre-treatment of the Vero cells prior to virus addition or post- treatment with 0.1% TTO after viral absorption did not significantly alter plaque formation (Carson et al. 2006).

TTO has an interesting antiviral activity against influenza A⁄PR⁄8 virus subtype H1N1 in Madin–Darby canine kidney (MDCK) cells. It has been found that TTO had an inhibitory effect on influenza virus replication at doses below the cytotoxic dose; terpinen-4-ol, terpinolene, and α-terpineol were the main active components (Garozzo et al. 2009).

The mechanism of action of TTO and its active components against Influenza A/PR/8 virus subtype H1N1 was investigated in MDCK cells. The effect of TTO and its active components on different steps of the replicative cycle of influenza virus was studied by adding the test compounds at various times after infection. These experiments revealed that viral replication was significantly inhibited if TTO was added within 2 h of infection, indicating an interference with an early step of the viral replicative cycle of influenza virus and suggesting that TTO could inhibit viral uncoating by an interference with acidification of intra-lysosomal compartment (Garozzo et al. 2011).

Antifungal activity

The antifungal activity of TTO was known anecdotally especially amongst the aboriginal people of Australia.

In 1998 Hammer et al. studied the in vitro TTO activity against Candida albicans and non-albicans Candida species. The minimum killing TTO concentration for killing isolates was 0.25% and 0.5% for

Candida albicans and non-albicans Candida species, respectively.

Mondello et al. (2003) investigated the in vitro antifungal activity of TTO (ISO 4730-2004) against clinical isolates of pathogenic yeasts including strains of Candida albicans resistant to fluconazole and/or itraconazole, as well as the in vivo activity in an experimental vaginal infection using fluconazole–itraconazole-susceptible or -resistant strains of Candida albicans. The susceptibility testing of Candida spp., and Cryptococcus neoformans to TTO, fluconazole and itraconazole was conducted using a microbroth method according to the National Committee for Clinical Laboratory Standards (NCCLS 1997) for both dilution antifungal susceptibility testing of yeasts (Liu et al. 2009).

TTO was active against all tested strains, with MICs ranging from 0.03% (for Cryptococcus neoformans) to 0.25% (for some strains of Candida albicans and other Candida spp.). Fluconazole- and/or itraconazole-resistant Candida albicans isolates had TTO MIC50s and MIC90s of 0.25% and 0.5%, respectively. The MIC90 for Candida albicans strains was found to be the same (0.25%) reported by Hammer et al. (1998) against the same fungus using a TTO mixture with relatively similar proportions of terpinen-4-ol and 1,8-cineole. Moreover neither fungistatic nor fungicidal activities were strongly influenced by lowering the pH of the incubation medium to pH 5, thus supporting the use of TTO for skin and mucosal infections.

The results of the in vivo investigations on the animal model (oophorectomized – ovary removal surgery female rats of the Wistar strain) of vaginal candidiasis demonstrated that TTO administered intravaginally using a dose volume of 0.1 ml at concentrations of 1%, 2.5% and 5% is effective in resolving experimental Candida albicans infection, with both fluconazole-susceptible and –resistant isolates. In the case of the fluconazole-susceptible organism, treatment with TTO was comparable to a standard treatment with fluconazole, used as positive control, whereas no effect was observed in rats treated with TTO diluted with polisorbate 80 used as negative control. The results showed that TTO exerted a marked acceleration of clearance of the yeast, as demonstrated by a statistically significant decrease in CFU counts in the first 2 weeks after the vaginal treatment, with a substantial TTO dose dependence of fungal clearance, although the difference was not statistically significant. With all dose regimens, the infection was cleared in 3 weeks, whereas the untreated control rats remained infected. TTO (5%) also caused a rapid clearance of the fluconazole-resistant strain from the vagina of experimentally infected rats. There was a statistically highly significant difference at all time-points considered between control (or fluconazole-treated rats) and those treated with TTO. Again the infection was resolved in 3 weeks by TTO, whereas all other animals, either untreated or fluconazole- treated, were still infected at the end of the 3 week period.

In a follow up study, Mondello et al. (2006) confirmed the previous result with the animal experimental model as reported on the in vivo activity of terpinen-4-ol, considered the main bioactive component of

TTO. Using the same methodology as detailed in their previous paper they concluded that terpinen-4-ol was a likely mediator of the in vitro and in vivo activity of TTO and claimed that their results were the first to demonstrate that terpinen-4-ol could control Candida albicans vaginal infections. They concluded that the purified compound held promise for the treatment of vaginal candidiasis, particularly the azole-resistant forms.

Antimycotic properties of TTO and its principal components were compared with the activity of 5- fluorocytosine and amphotericin B. The majority of the organisms were sensitive to the essential oil, with TTO and terpinen-4-ol being the most active oils showing antifungal activity at minimum inhibitory concentration values lower than other drugs (Oliva et al. 2003).

The in vitro activities of TTO against Malassezia yeast species were shown. Ketoconazole was the most active of the imidazoles in the agar dilution assay, followed by miconazole and econazole, which were similar in activity. Malassezia furfur was the least susceptible species. Malassezia sympodialis,

Malassezia slooffiae, Malassezia globosa, and Malassezia obtusa showed similar susceptibilities. Tea tree oil was active against all Malassezia species, for which the MICs were similar. Ketoconazole was also the most active of the imidazoles in the broth dilution assay. Miconazole and econazole showed similar activities against each species, but demonstrated differences in activity between species. The MICs of tea tree oil were similar for M. furfur and M. sympodialis, but the minimum fungicidal concentrations (MFCs) were several dilutions lower for M. furfur. The authors concluded that individual Malassezia species vary in their susceptibility to several antifungal agents, with M. furfur being the least susceptible of the species tested, whereby TTO may be a suitable alternative topical agent (Hammer et al. 2000).

In another study investigating in vitro antifungal activity of TTO components, the highest activity, with minimum inhibitory concentrations and minimum fungicidal concentrations of <0-25%, was shown by terpinen-4-ol, α-terpineol, linalool, α-pinene and β-pinene, followed by 1,8-cineole. All TTO components, except β-myrcene, had antifungal activity. This study identified that most components of TTO have activity against a range of fungi (Hammer et al. 2003b).

Carson et al. (2006) summarised the antifungal activity of TTO against a range of fungal species published by a number of researchers obtained from over 15 papers: MICs were in the range between 0.03 and 0.5% and fungicidal concentrations from 0.12 to 2%. The exception to these ranges was Aspergillus niger with MFC values up to 8%. However the authors noted that these assays were conducted with fungal conidia that are known to be relatively impervious to chemical agents. Subsequent assays show that germinated conidia are significantly more susceptible to TTO than non- germinated conidia. They also noted that TTO vapours have also been demonstrated to inhibit fungal growth and affect sporulation.

Hammer et al. (2004) investigated the mechanism of action of TTO and its components against

Candida albicans, C. glabrata and Saccharomyces cerevisiae. Yeast cells were treated with TTO or components, at one or more concentrations, for up to 6 hours. During that time, alterations in permeability were assessed by measuring the leakage of 260 nm absorbing materials and by the uptake of methylene blue dye. Membrane fluidity was measured by 1,6-diphenyl-1,3,5-hexatriene fluorescence. The effects of TTO on glucose-induced medium acidification were quantified by measuring the pH of cell suspensions in the presence of both TTO and glucose. The results showed that treatment of Candida albicans with TTO and its components at concentrations of between 0.25 and 1.0% altered both permeability and membrane fluidity. Membrane fluidity was also increased when Candida albicans was cultured for 24 hours with 0.016%-0.06% TTO, as compared with control cells. For all three organisms, glucose-induced acidification of the external medium was inhibited in a dose- dependent manner in the presence of TTO at concentrations of 0.2%, 0.3% and 0.4%. It was

concluded that the data from the study supported the hypothesis that TTO and components exert their antifungal actions by altering membrane properties and compromising membrane-associated functions.

Antiseptic and disinfectant activity

Effective skin antisepsis and disinfection are key factors in preventing many healthcare-acquired infections associated with skin microorganisms, particularly Staphylococcus epidermidis. The antimicrobial efficacy of chlorhexidine digluconate, a widely used antiseptic in clinical practice, alone and in combination with TTO was studied. Chlorhexidine digluconate exhibited antimicrobial activity against Staphylococcus epidermidis in both suspension and biofilm (MIC 2–8 mg/l) as well as TTO (2– 16 g/l), but no synergistic effect was found for combination of chlorhexidine digluconate with TTO (Karpanen et al. 2008).

A study was conducted to determine the frequencies at which single-step mutants resistant to TTO and rifampicin occurred amongst the Gram-positive organisms Staphylococcus aureus, Staphylococcus. epidermidis and Enterococcus faecalis. For TTO, resistance frequencies were very low at <10−9. Single- step mutants resistant to TTO were undetectable at two times the MIC for Staphylococcus aureus RN4220 and derivative mutator strains or at 3× MIC for the remaining Staphylococcus aureus strains, including a clinical MRSA isolate. Similarly, no mutants were recovered at 2× MIC for Staphylococcus. epidermidis or at 1× MIC for E. faecalis. Resistance frequencies determined in vitro for rifampicin (8× MIC) ranged from 10−7 to 10−8 for all isolates, with the exception of the Staphylococcus aureus mutator strains, which had slightly higher frequencies. Data suggest that Gram-positive organisms such as Staphylococcus spp. and Enterococcus spp. have very low frequencies of resistance to TTO (Hammer et al. 2008).

An investigation was carried out to determine the effect of Burnaid, a commercial TTO preparation, against Enterococcus faecalis ATCC29212, Staphylococcus aureus ATCC29213, Escherichia coli

ATCC25922 and Pseudomonas aeruginosa ATCC27853.The organisms were suspended in sterile saline (density of 0.5 McFarland Standard) and inoculated onto horse blood agar (E. faecalis and

Staphylococcus aureus) or Mueller-Hinton agar (Escherichia coli and P. aeruginosa). 100 µl of Burnaid unsterilized, Burnaid sterilized and the base product (Tinasolve™) were placed in duplicate in wells cut into the agar plates. Sterility and inactivation cultures were also performed on the samples. None of the samples were found to be contaminated with bacteria prior to testing. Only Staphylococcus aureus and Escherichia coli showed zones of growth inhibition around the Burnaid and Tinasolve. Zones of growth inhibition (22 mm) were similar for the active product (Burnaid) and the base (Tinasolve™). There was no bactericidal activity against E. faecalis or P. aeruginosa. In view of these findings and literature indicating the cytotoxicity of TTO against human fibroblasts and epithelial cells, it is recommended that this product should not be used on burn wounds (Faoagali et al. 1997).

Assessor’s comment: This study suggests not using TTO preparations for the care of burn wounds.

Antiprotozoal activity

Carson et al. (2006) reported that results have been published showing that TTO has antiprotozoal activity. TTO caused a 50% reduction in growth (compared to controls) of the protozoa Leishmania major and Trypanosoma brucei at concentrations of 403 mg/ml and 0.5 mg/ml, respectively. TTO at high concentration corresponding to 300 mg/ml killed all cells of Trichomonas vaginalis and there is also anecdotal in vivo evidence that TTO may be effective in treating T. vaginalis infections.

3.1.2. Secondary pharmacodynamics

Antitumor activity

The potential anti-tumoral activity of TTO, distilled from Melaleuca alternifolia, was analysed against human melanoma M14 WT cells and their drug-resistant counterparts, M14 adriamicin-resistant cells. Both sensitive and resistant cells were grown in the presence of TTO at concentrations ranging from 0.005 to 0.03%. Both TTO and its main active component terpinen-4-ol were able to induce caspase- dependent apoptosis of melanoma cells and this effect was more evident in the resistant variant cell population. Freeze-fracturing and scanning electron microscopy analyses suggested that the effect of the crude oil and of the terpinen-4-ol was mediated by their interaction with plasma membrane and subsequent reorganization of membrane lipids. In conclusion, TTO and terpinen-4-ol were able to impair the growth of human M14 melanoma cells and appear to be more effective on their resistant variants, which express high levels of P-glycoprotein in the plasma membrane, overcoming resistance to caspase-dependent apoptosis exerted by P-glycoprotein-positive tumour cells (Calcabrini et al. 2004).

Human melanoma cells (M14 WT) grown in the presence of the antitumor drug adriamycin (M14 ADR) express the multidrug transporter P-gp. TTO and terpinen-4-ol proved to be capable of inhibiting the growth of melanoma cells and of overcoming multidrug resistance. The major inhibitory effect was found after treatment with 0.01% terpinen-4-ol. The effect of TTO on melanoma cells appears to be mediated by its interaction with the lipid bilayer of the plasma membrane. The experiments indicate that TTO and its main active component, terpinen-4-ol, can also interfere with the migration and invasion processes of drug-sensitive and drug-resistant melanoma cells (Bozzuto et al. 2011).

Liu et al. (2009) reported that TTO showed strong in vitro cytotoxicity towards human lung cancer cell line (A549), human breast cancer cell line (MCF-7) and human prostate cancer cell line (PC-3) with IC50 values (24 hr incubation) of 0.012%, 0.031% and 0.037%, respectively.

Antioxidant activity

The antioxidant activity of Australian TTO was determined using two different assays. In the 2,2- diphenyl-1-picrylhydrazyl assay, 10 µl/ml crude TTO in methanol had approximately 80% free radical scavenging activity, and in the hexanal/hexanoic acid assay, 200 µl/l crude TTO exhibited 60% inhibitory activity against the oxidation of hexanal to hexanoic acid over 30 days. The results indicate that TTO has an antioxidant activity. Inherent antioxidants, i.e., R-terpinene, R-terpinolene, and γ- terpinene were separated from crude TTO and identified chromatographically using silica gel open chromatography, C18-high-pressure liquid chromatography, and gas chromatography-mass spectrometry. Their antioxidant activities decreased in the following order in both assays: α-terpinene > α-terpinolene > γ-terpinene (Kim et al. 2004).

Estrogenic activity

Following 3 case reports of gynecomastia in prepubertal boys (4, 7, and 10 years old) after repeated topical use of products containing lavender, one of them in combination with TTO, in vitro studies on estrogenic and anti-androgenic activity of both essential oils separately were performed. It was shown that they exert in vitro apparently dose-related oestrogen-like activity by inducing growth in MCF-7 cells and anti-androgenic effects by increasing luciferase activity in breast-cancer (MDA-kb2) cells in presence of the androgen-receptor agonist dihydrotestosterone (DHT) at 0.1 nM. Other components in the products used by the boys may also possess endocrine-disrupting activity that contributed to the gynecomastia, but those components were not tested because lavender oil was the only one present in all the products and TTO was considered chemically similar (Henley et al. 2007).

The estrogenic potential of TTO was confirmed with a similar in vitro experimental model. However, the only three constituents of TTO which demonstrated through an in vitro dermal penetration study to be able to penetrate human skin to any measurable degree (terpinen-4-ol, α-terpineol and eucalyptol) did not show any estrogenic activity when analysed separately and as mixture in a ratio penetrating the

skin. It was concluded that the components of TTO which responsible of the estrogenic potential in vitro may not be bioavailable (Nielsen 2008).

Also the SCCP in its opinion concluded that the estrogenic potential of TTO shown in vitro is not supported by in vivo studies to elucidate the relevance of this finding for the in vivo situation. Moreover, since the hormonal active ingredients of TTO were shown not to penetrate the skin, the hypothesized correlation of the finding of 3 cases of gynecomastia to the topical use of TTO is considered implausible (SCCP 2008).

3.2. Overview of available pharmacokinetic data regarding the herbal substance(s), herbal preparation(s) and relevant constituents thereof

TTO contains terpenes, sesquiterpenes, hydrocarbons, and related alcohols. Because of the high lipophilicity of its components it has been postulated that TTO is likely to be rapidly and completely absorbed from the skin and mucous membranes (ESCOP 2009). On the other hand, in vitro experiments indicated that, after application of TTO to human epidermal membranes mounted in diffusion cells in the pure form and as a 20% solution in ethanol, only a small proportion of the applied amount (2-4% and 1.1-1.9% respectively) penetrated into or through human epidermis (Cross et al. 2008).

The major compound of TTO, terpinen-4-ol, is able to permeate human epidermis. The permeation depends on the applied preparation whereas a semisolid O/W emulsion or an ointment is superior to a cream (Reichling et al. 2006). The skin absorption rate of TTO was investigated in vitro using diffusion cell permeation experiments with heat separated human epidermis to evaluate the capability of terpinene-4-ol, the main component of the oil, to permeate human skin. Flux values (the absorption rate per unit area, μl/cm2 h) of three different semisolid preparations containing 5% TTO were 0.067 for an oil/water emulsion, 0.051 for white petrolatum and 0.022 for a cream. Apparent permeability constants (Papp cm/s) can be calculated from flux values, taking the applied drug concentration into account. Papp values for the cream (2.74) and pure oil (1.62) were quite comparable, whereas white petrolatum (6.36) and the semi-solid oil/water emulsion (8.41) gave higher values indicating penetration enhancement (Reichling et al. 2006).

Considerable research has been done on the metabolism of monoterpenes. After dermal and/or oral absorption, liver P450 mono-oxygenases are involved in biotransformation. Subsequently, 60-80% of absorbed monoterpenes are excreted as glucuronides (Villar et al. 1994).

Cal and Krzyaniak (2006), Cal et al. (2006) and Cal (2008) studied the penetration behaviour of TTO and pure constituents using a flow-through diffusion cells, human skin preparations and in vivo human studies which represented infinitive dose and occlusive application conditions. Application times of 1, 4 or 8 hours. Neat TTO, neat terpene-4-ol and 5% terpene-4-ol (grape seed oil/carbomer hydrogel and o/w emulsion) were tested. After the exposure period, the receptor fluid and skin layers were analysed in the in vitro studies and the skin layers in the in vivo studies. TTO or pure terpene-4-ol caused a significant increase in the skin accumulation of terpene-4-ol in the hydrophilic skin layers (dermis and epidermis). In contrast to the results of Cross et al. (2008) and Reichling et al. (2006) which used only epidermis, terpene-4-ol was not detected in the receptor fluid at any stage of the study of Cal et al. (2006) which utilised epidermal and dermal layers. TTO or pure terpene-4-ol caused a significant increase in the skin accumulation of terpene-4-ol in the hydrophilic skin layers (dermis and epidermis). These sets of data, accumulation in the skin layers and diffusion into the acceptor fluid, suggest that in vivo terpene-4-ol may penetrate into the blood circulation.

Assessor’s comment: In conclusion, the process of terpene penetration into the skin and through the skin can be considered to be strongly dependent on the experimental model used (choice of

membrane, hydration level and dose) and on the carrier for the penetrating terpene, while in vivo the effect of evaporation – shown to be 98% needs to be considered.

3.3. Overview of available toxicological data regarding the herbal substance(s)/herbal preparation(s) and constituents thereof

3.3.1. Single dose toxicity

The acute oral LD50 in rats has been reported as 1.9-2.6 ml/kg (1.4-2.7 g/ kg of b.w.) (Hammer et al. 2006, Carson et al. 1998, Halcón & Milkus 2004). Rats receiving 1.5 g/kg or more appeared lethargic and ataxic 72 hours post dose. By day 4 all but one animal at this dose had regained locomotor function (Hammer et al. 2006).

No acute inhalation toxicity was evident in response to exposure with TTO/ethanol/CO2 in rats, but methodological weaknesses with the study were noted (SCCP, 2008).

Postulated lethal dose for a 3-year-old child was calculated to be 26 ml (Halcón & Milkus 2004).

The dermal LD50 in rabbits is > 5 g/kg (Council of Europe Committee of Experts on Cosmetic Products 2001).

3.3.2. Repeated dose toxicity

No deaths or toxic effects were reported in a 30 days-skin irritation study in rabbits using a 25% TTO in liquid paraffin other than slight initial irritation (Council of Europe Committee of Experts on Cosmetic Products 2001).

Renal toxicity has been observed in separate studies following oral administration of terperne-4-ol, cineole and cumene (similar to p-cymene). Taking into consideration the typical levels of these components in TTO, a NOEL of 117 mg/kg/day has been theoretically estimated for TTO (Nielsen 2005).

This conclusion could be substantiated by available information on repeated dose systemic toxicity of TTO constituents. Based on repeated-dose toxicity data in literature, the SCCP in 2008 has established NOAEL values in animals of six main components in Tea Tree Oil. These NOAEL’s have been summarized in the table below (Norwegian Food Safety Authority (Matthylsyne) 2012):

Terpinen-4-ol did not induce changes in the morphology or function of the kidneys of male Sprague- Dawley rats following 28 days of repeated oral exposure to 400 mg/kg b.w. and was considered to be non-toxic (Schilcher & Leuschner 1997). Thus the NOAEL after oral exposure may be estimated to be 400 mg/kg.

Cineole given to B6C3F1 mice by gavage for 28 days at doses up to 1200 mg/kg/day did not result in any changes. When given encapsulated at doses corresponding to 600 – 5607 mg/kg/day, some hypertrophy of hepatocytes was seen, but was not considered significant (National Toxicology

Program, cited in De Vincenzi et al. 2002). Cineole (8 or 32 mg/kg b.w. was given by gavage to male SPF CFLP mice 6 days per week for 80 weeks. No changes were evident in mice given cineole when compared to control mice (Roe et al. 1979). Based on the studies on hepatic and renal toxicity evaluated by BIBRA (British Industrial Biological Research Association), a NOAEL for cineole might be estimated as 300 mg/kg b.w., which is in agreement with the evaluation from the Norwegian Food Control Authorities in 1999 (EFSA 2012).

Based on the available information on repeated dose systemic toxicity of TTO constituents, the SCCP opinion estimated a derived NOAEL for TTO of 117 mg /kg b.w. /day for renal effects (SCCP 2008, Norwegian Food Safety Authority (Matthylsyne) 2012).

Several reports of oral toxicity can be found in the literature. Data indicate that due to its systemic toxicity, TTO should only be used as a topical agent.

General toxicology profile of TTO indicates that severe reactions would be extremely rare if TTO is not ingested (Halcón & Milkus 2004).

3.3.3. Genotoxicity

TTO produced a negative result in the in vitro Ames test (Saller et al. 1998). In December 2004 the Scientific Committee on Consumer Products (SCCP) noted that TTO is not mutagenic in the Ames test although they stated that there were insufficient details of the study and the study was deemed inadequate. They further noted that, as TTO has antimicrobial properties, an Ames test would be of limited value (SCCP 2004).

In 2005 Evandri et al. evaluated the mutagenic and antimutagenic activity of essential oils TTO and Lavandula angustifolia (lavender oil) the bacterial reverse mutation assay in Salmonella typhimurium TA98 and TA100 strains and in Escherichia coli WP2 uvrA strain, with and without an extrinsic metabolic activation system. The results showed that neither essential oil had mutagenic activity on the two tested Salmonella strains or on Escherichia coli, with or without the metabolic activation system, providing further evidence of the lack of mutagenic potential of TTO.

These results were also supported by a paper published by Fletcher et al. (2005) using Salmonella strains TA102, TA100 and TA98 in the Histidine Reversion Assay Ames test: neither TTO nor terpinen- 4-ol, one of the major constituents of TTO, induced reverse mutations in any of the tester strains examined with or without metabolic activation, confirming that they are not mutagens.

Two papers were found evaluating the mutagenic potential of TTO components:

Gomes-Carneiro et al. (2005) investigated the genotoxicity of β-myrcene, α-terpinene and (+) and (-)- α-pinene by the Salmonella/microsome assay (TA100, TA98, TA97a and TA1535 tester strains), using a plate incorporation procedure without and with addition of an extrinsic metabolic activation system (rat liver S9 fraction induced by Aroclor 1254) and concluded that these common constituents of essential oil are not mutagenic in the Ames test.

Hammer et al. (2006) in a review noted that the following components were non-mutagenic in the Salmonella/microsome (Ames) test or the Bacillus subtilis rec- assay: terpinen-4-ol, α-terpinene, 1,8- cineole, cymene, limonene, α -pinene, β-pinene, linalool and β -myrcene. In contrast, terpineol caused a slight but dose related increase in the number of revertants with the TA102 tester strain both with and without S9 mixture. However, no significant effect was seen in the other three bacterial strains, indicating that terpineol induced a base-pair substitution affecting an A–T base pair.

In tests with mammalian cells (comet assay), γ-terpinene did not increase DNA strand breakage in human lymphocytes at 0.1 mM but did at concentrations starting from 0.2 mM. Cineole, D-(+)-

limonene, linalool, l-phellandrene and β -pinene at concentrations ranging from 10 to 1000 μM did not increase the frequency of spontaneous sister-chromatid exchanges in Chinese hamster ovary cells. Another study showed linalool to be non-mutagenic using a Chinese hamster fibroblast cell line. β- myrcene did not have mutagenic activity when tested with human lymphocytes and was not genotoxic in bone marrow cells of rats administered β -myrcene orally.

They concluded that, overall, the available data on the mutagenicity of TTO and its individual constituents indicate low mutagenic potential, using both bacterial and mammalian test systems (Hammer et al. 2006).

In contrast γ-terpinene was shown to protect lymphocytes against IQ- and MMC-induced DNA damages at concentrations lower than 0.2 mM (Aydin et al. 2005)

An in vivo Mouse Micronucleus Assay (ICP Firefly Pty Ltd. 2005) was conducted according to OECD Test Guideline No. 474, which was conducted under GL. TTO was administered by gavage at 1000, 1350 and 1750 mg/kg b.w. TTO. There were no increases in the frequency of micronucleated cells in any of the dose groups. There was a statistically significant depression of PCE viability and PCE+NCE ratio (P<0.001) in the high dose group in both sexes when compared with the vehicle control groups at 48 hours. This finding is an indication that there was sufficient exposure of the bone marrow to the test substance to elicit a response. Clinical signs in the high dose group included depressed weight gain, wobbly gait, laboured breathing and rough coat.

TTO in concentrations ranging from 95 μg/ml to 365 μg/ml increased neither the frequencies of micronuclei nor the frequencies of chromosomal aberrations in human lymphocytes. Higher concentrations could not be tested, since at higher concentrations cell viability was significantly reduced. Within that limitation, these results suggest that TTO does not induce chromosome aberration (Pereira et al. 2014).

3.3.4. Carcinogenicity

No available data.


The Scientific Committee on Consumer Products in its updated “Opinion on Tea Tree Oil” in 2008 stated that since methyleugenol was reported as a minor constituent of TTO “the content should be indicated. According to the opinion SCCNFP/0373/00 on methyleugenol in fragrances the content in finished leave-on products should not exceed 0.0002% (2 ppm) and in rinse-off products 0.001% (10 ppm).”

This statement follows the EMEA “Public statement on the use of herbal medicinal products containing methyleugenol” (2005) reporting a content of 0.28 to 0.9% of the natural potential carcinogen methyleugenol in TTO. However HMPC has concluded that “the present exposure to methyleugenol resulting from consumption of herbal medicinal products (short time use in adults at recommended posology) does not pose a significant cancer risk.”

The Australian TTO industry reports that these levels of methyleugenol refer to Melaleuca bracteata, whereas commercial TTO is derived solely from Melaleuca alternifolia; analytical surveys conducted by Australian TTO industry show that Melaleuca alternifolia contains only trace levels of methyleugenol.

Southwell et al. (2011) quantified the traces of methyleugenol previously reported in TTO ranging from less than 0.01% to 0.06% (mean 0.02%).

3.3.5. Reproductive and developmental toxicity

No data available on TTO.

However, exposure to α-terpinene (125 or 250 mg/kg b.w.), present at approximately 9% in TTO, for nine consecutive days caused decreased body weight gain in pregnant Wistar rats. The offspring of dams given 60 mg/kg b.w. from day 6 to day 15 of pregnancy had delayed ossification and skeletal malformations. At 30 mg/kg b.w. no effects were seen on either dams or offspring. Effects at doses higher than 60 mg/kg b.w. were accompanied by maternal toxicity. The authors suggested a NOAEL for embryofoetotoxicity of 30 mg/kg b.w. for oral exposure of rats to α-terpinene (Araujo et al. 1996). These limited data suggest that TTO is potentially embryofoetotoxic, although only if ingested at relatively high levels (Araujo et al. 1996).

Hammer et al. (2006), noted that the embryofoetotoxicity of α-terpinene (normally present in TTO at 9%) has been evaluated and found that at oral doses of greater than 60 mg/kg b.w. there was delayed ossification and skeletal malformations in the foetuses and this was accompanied by maternal toxicity. The test material was administered to rats from day 6 to day 15 of gestation. The authors concluded that TTO is potentially embryofoetotoxic although only if orally ingested at relatively high doses.

3.3.6. Local tolerance

Skin irritation

Two studies were conducted on groups of 3 female rabbits of the New Zealand strain according to the methodology detailed in OECD guideline 404 and were GLP compliant. In the first study TTO (100%) was applied undiluted on 4×4 cm patches. In the second study, dilutions of 75-12.5% TTO were applied for 4 hours with a semi-occlusive patch application followed by a 14 days observation period. The results showed that, in the first study, TTO (100%) was found to be a mild irritant at 60 minutes post exposure, a severe irritant at 24 and 48 hours, a moderate irritant at 72 hours and a mild irritant 7 and 14 days following a 4 hour semi-occlusive patch application on intact skin. At 21 days the skin had returned to normal. In the second study, TTO (75%) was found to be a mild to moderate irritant, TTO (50%) was found to be a minimal irritant. TTO (at 25% and 12.5%) was found to be a non-irritant (SCCP December 2004).

Draize skin irritancy index was found to be 5.0, based on application of 100% TTO to intact and abraded skin of albino rabbits, thus signifying that TTO could cause dermatitis in some users (Halcón & Milkus 2004).

The acute dermal LD50 in rabbits was recorded as in excess of 5.0 g/kg since this dose resulted in 2/10 deaths in rabbits. Furthermore, it was observed at necropsy that neat TTO produced irritant effects and skin abnormalities in rabbits patch tested at this dose for 24 h with occlusion. Pure (100%) TTO applied to the skin of albino rabbits and maintained at 2 g/kg for 24 hours resulted in no signs of toxicity (Halcón & Milkus 2004).

A 30-day dermal irritation test in rabbits using 25% TTO in paraffin on shaved skin did not result in visible signs of irritation. Therefore, TTO should not be used for conditions where skin irritability is already present (e.g. dermatitis) (Halcón & Milkus 2004).

Eye irritation

The primary eye irritation of TTO was also studied in the rabbit (female, Japanese White) under GLP conditions. Two groups of three rabbits were given a single ocular dose (0.1 ml) of TTO (1% or 5% in liquid paraffin). After instillation of the test substance, no abnormal signs in the clinical conditions were observed among the rabbits. Ocular responses using Draize’s criteria demonstrated a conjunctival

discharge lasting for up to six hours following instillation of 1% TTO and conjunctival redness and discharge for up to 24 hours following instillation of 5% TTO. In both groups, the maximal response was observed after one hour. Based on these observations, the author concludes, that both TTO solutions can be classified as “minimally irritating” (SCCP 2008).


TTO was found to produce ototoxicity when applied in the ears of guinea pigs at 100% concentration, but no ototoxicity was found for 2% solutions (Halcón & Milkus 2004).

Skin sensitisation potential

In order to test the potential of TTO to cause skin sensitisation guinea pigs were pre-treated 2 times via intradermal injections and an epidermal induction application of the oil. Two weeks after the induction application, the animals were tested on one flank with the maximum sub-irritant concentration of the oil. No irritant response was observed (Halcón & Milkus 2004).

A guinea pig maximization assay using the Magnusson and Kligman method (Pharmaceutical Consulting Service 1989) and albino guinea pigs (20 per group) has been conducted with TTO. During the induction phase, two 0.1 ml intradermal injections were given to the animals. One week later, 5% TTO was applied to the skin at the injection site under occlusion for 48 hours. After a two week period, a 30% TTO challenge dose was applied to the skin under occlusion for 48 hours. There was no evidence of sensitisation in this assay. In a published report, TTO of unknown quality was tested in 10 guinea pigs using an adjuvant maximization protocol. The induction concentration was not given. At an elicitation concentration of 30%, 3/10 guinea pigs gave positive reactions at the 48-hour reading. At 10%, no reactions were observed. The main component of TTO, terpinen-4-ol, gave no response when cross-challenged in the reacting animals. These results may indicate that TTO may be a weak skin sensitizer. The disagreement between the two studies cannot be explained, other that it could have been the result of different quality and oxidation state of the TTO tested.

Three samples of TTO were tested in the Mouse Local Lymph Node Assay (LLNA) (RCC Ltd. Study A69041, Study A78682, Study A78816 2006). Two of the samples were non-oxidised, undegraded oil, while the third was a severely oxidised and degraded. The EC3 (calculated concentration of the test substance which elicited a three-fold increase in the Stimulation Index) values of 24.3% and 25.5% were obtained with the two undegraded oil samples, while the EC3 of the degraded oil was 4.4%. There was a clear dose-response in each case. Another sample of undegraded TTO was sent to a different laboratory (MB Research Laboratories 2007) which could perform immunophenotyping of the lymphocytes. An EC3 value of 8.3% was calculated in this LLNA. Similarly the %B cells, %T cells, and B:T ratio indicated a sensitising response. Overall, these results show that undegraded TTO has a weak potential for sensitisation in this assay system. Degraded TTO had 5-times higher potency, but would still be regarded as a moderate sensitizer.

The peroxide value and p-cymene content are particular useful indicators of the age of the oil and the extent of degradation (Southwell 2006). The peroxide value is a measure of available oxygen, i.e. how much one or more components of the oil have absorbed oxygen in the form of peroxide. Therefore, the Peroxide Value is an indicator of the presence of peroxides. Generally, good quality fresh oils will have a peroxide value below 10 µeq O2. Peroxides degrade over time and the degradation products, such as 1,2,4-trihydroxymenthane, may have a high irritation and sensitisation potential. The peroxide value will fall as the peroxides decompose. A very old (>10 years old), decomposed oil could have a low peroxide value. Such an oil will have elevated levels of the decomposition products and potentially elevated p-cymene (16% plus). p-Cymene, occurs naturally in TTO (typically 0.5 – 8%).

Southwell (2006) examined 26 TTO samples and demonstrated that the presence of 1,2,4- trihydroxymenthane in TTO is a rare event and in the cases where this breakdown product was found, the oils were extremely old and severely degraded to the extent where the oils would not be compliant to the ISO Standard. Even in extremely degraded oils, 1,2,4-trihydroxymenthane concentrations were less than 5%. Consequently, although 1,2,4-trihydroxymenthane can be detected by GC and GC/MS in aged TTOs, when concentrations are low (<1%), the triol peak can easily be hidden by other 37 oil peaks in the same region and therefore the presence of 1,2,4-trihydroxymenthane is not suitable to check possible degradation of TTO. The use of other degradation products as degradation markers is even more difficult as it has not been possible to consistently and positively identify ascaridole, ascaridole glycol, the keto-epoxide and the di-epoxide that have been tentatively identified in degraded TTOs as well as these products being present in even smaller concentrations than the triol. Furthermore, Southwell also demonstrated a relationship between the levels of p-cymene and 1,2,4- trihydroxymenthane. Thus, Southwell has proposed monitoring the degradation status of TTO by using p-cymene as a reliable marker.

For many years, 1,8-cineole was regarded as an undesirable constituent in TTO due to its reputation as a skin and mucous membrane irritant. However, other studies suggested that this component is not responsible for a large proportion of sensitivity reactions (Carson et al. 1998).

Oxidation products are the likely allergens. Since oxidized TTO appears to be a more potent allergen than fresh TTO, human adverse reactions may be minimized by reducing exposure to aged, oxidized oil (Carson & Riley 2001).


Although some irritation was observed, undiluted TTO did not produce phototoxic effects on the skin of hairless mice (Carson et al. 1998).

3.3.7. Other special studies


A case report documented TTO poisoning after a single dermal application of 120 ml of undiluted TTO to 3 adult intact female purebred Angora cats, one of which died. The cats were severely infested with fleas, so they were shaved and the oil was applied directly to the cats’ skin. The shaving produced no nicks on the skin; however, numerous flea bites were visible. The product used to eliminate fleas was labelled for use as a spot treatment for skin lesions, but a catalogue advertised that it would repel fleas when diluted and used as a dip. All animals exhibited hypothermia, incoordination, dehydration and trembling. The surviving 2 cats recovered after 1-2 days (Bischoff & Guale 1998). Neurotoxicity and death have been observed in cats exposed to very high doses of TTO by the dermal route. However, the possibility that these animals were also exposed by the oral route by licking of the skin and fur of the application area cannot be ruled out.

Villar et al. (1994) reported that cases of TTO toxicosis have been reported by American veterinarians to the National Animal Poison Control Centre when the oil was applied on derma of dogs and cats. They noted that, in most cases, the oil was used to treat dermatologic conditions at inappropriate high doses. The typical signs observed were depression, weakness, incoordination and muscle tremors. Treatment of clinical signs and supportive care was sufficient to achieve recovery without sequelae within 2-3 days.

Cytotoxicity studies

TTO and components of TTO was tested on several human cell lines in vitro. Cytotoxicity with 100% TTO ranged from 0.02 to 2.8 g/l, with epithelial-like cells being the most robust, and liver-derived cells being the most susceptible. Cytotoxicity for the components of TTO was as follows: 1,8-cineole, from 0.14 to 4.2 g/l; terpinen-4-ol, from 0.06 to 2.7 g/l; α-terpineol, 0.02 to 1.1 g/l. These data suggest that topical use of TTO is suitable, as epithelial cell seem to be the most resistant cells to its potential cytotoxicity (Halcón & Milkus 2004).

3.4. Overall conclusions on non-clinical data

Studies on TTO demonstrate that adequate doses have broad spectrum antimicrobial activity with little evidence for inducing tolerance and resistance. There is also some evidence of TTO possessing anti- inflammatory activity.

The cytotoxic activity towards a range of cancer cell types shown by means of in vitro studies is not considered relevant for the purpose of this assessment.

The published pharmacokinetic data on TTO are minimal. In vitro skin permeation studies using human skin preparations demonstrate that the extent of penetrating of TTO components is very low, with the more polar terpenen-4-ol and α-terpineol being the only components which penetrate to any appreciable levels. The total penetration of TTO is 2-4% and 7% of applied dose under non-occluded and partly occluded conditions. Under infinite dose, occluded conditions terpenen-4-ol can cumulate within the skin which may act as a reservoir for gradual elimination into the circulation. However, these conditions are not representative of the typical use pattern of TTO. As TTO oil is a semi-volatile substance, the majority of the applied dose rapidly evaporates from the surface of the skin before it has the chance to absorb into the skin.

TTO has been reported to cause mild to moderate skin irritation in rabbit studies. Local lymph node assay (LLNA) studies indicate that TTO has mild skin sensitisation potential. Highly degraded TTO has a greater potential for skin sensitisation due to the presences of oxidation by-products. Proper storage and handling of TTO and its formulated products are needed to avoid the development of these byproducts and reduce the risk of skin irritation and sensitisation in sensitive individuals (Nielsen 2005).

There are no oral repeated dose toxicity studies available for TTO. However, there are no known indications which require oral administration of TTO. The main route of administration is by dermal application. Repeated dose data are available on some of the main components of TTO. Renal toxicity has been observed in separate studies following oral administration of terperne-4-ol, cineole and cumene (similar to p-cymene). Taking into consideration the typical levels of these components in TTO, a NOEL of 117 mg/kg/day has been theoretically estimated for TTO (Nielsen 2005).

TTO was negative in the Ames assay using Salmonella typhimurium TA102, TA100 and TA98 examined with or without metabolic activation and not genotoxic in in vitro mammalian cells in concentrations ranging from 95 μg/ml to 365 μg/ml (Pereira et al. 2014). It did not induce clastogenicity in the in vivo mouse micronucleus assay (Fletcher et al. 2005).

Available data on the genotoxicity indicate low genotoxic potential of its major constituents, α-terpineol and γ-terpinene, in bacterial or mammalian test systems. α-Terpineol is slightly mutagenic but only in Salmonella typhimurium strain TA102. γ -Terpinene is slightly clastogenic. When tested by the comet assay, it induced DNA damage in human lymphocytes at concentrations starting from 0.2 mM (Aydin et al. 2005).

The slight genotoxic potential of α-terpineol and γ -terpinene do not seem to lead to a carcinogenic effect, since both compounds are not listed as carcinogens in IARC and NTP databases.

There are no experimental data on the mutagenic and clastogenic potential of terpinolene (= δ- terpinene, cas nr 586-62-9). This seems not to be a concern, since no genotoxic effects have been reported for TTO, which may contain up to 5% terpinolene. In addition, terpinolene is not listed as a carcinogen in IARC and NTP databases.

While TTO contains trace levels of methyleugenol, the typical use pattern in adults, being short-term dermal use is not expected to pose a significant cancer risk (Nielsen 2005).

4. Clinical Data

4.1. Clinical Pharmacology

4.1.1. Overview of pharmacodynamic data regarding the herbal substance(s)/preparation(s) including data on relevant constituents

The mechanisms of antimicrobial action elucidated so far reflect the terpenic hydrocarbon composition and indicate that cytoplasmic membrane integrity is compromised by treatment with TTO or some of its major components. Alterations in eukaryotic cell membranes have also been observed with TTO and terpinen-4-ol treatment (Longbottom et al. 2004, Calcabrini et al. 2004).

Pharmacological studies in humans

Pharmacological studies conducted in humans have been discussed in the ESCOP Monograph Supplement 2009. Messager et al. 2005 reported on the antimicrobial activity of TTO for hand cleansing. Koh et al. 2002 and Pearce et al. 2005 reported on the anti-allergenic and anti-inflammatory effects of TTO on histamine and nickel-induced skin reactions.

Khalil et al. 2004 have also investigated the regulation of wheal and flare by undiluted TTO on histamine-induced skin responses in human skin. 18 subjects had 25 μl of 100% TTO applied topically to the histamine-induced reaction site at 10 minutes and 20 minutes after histamine injection intradermally to the inner forearm skin. One arm of each subject was the study arm and the other arm (randomly allocated) was the control arm with no control oil applied to the reaction site. The TTO significantly reduced both the flare and wheal response at 30 minutes and 50 minutes respectively after histamine injection. No adverse effects were reported.

Canyon & Speare 2007 conducted head lice (Pediculus humanus var. capitis) avoidance experiments on the arm of the researcher. Circles of skin (2.5 cm in diameter) were marked out and test materials were applied to a test area. These test materials consisted of 100% TTO, a variety of other oils, neem insect repellent, N,N-Diethyl-3-methylbenzamide (DEET) 69.75 g/l (positive control) and KY-Jelly, inert lubricant gel (negative control). After 2 minutes, 15 lice were placed onto each treated area. TTO repelled 55% of head ice from treated area, followed by peppermint oil (34%) and DEET (26%). TTO was most effective at preventing lice from feeding (60%) followed by lavender oil (40%), peppermint (28%) and DEET (23%).

A summary of these studies is presented in Table 4.

Table 4: Pharmacological studies in humans

4.1.2. Overview of pharmacokinetic data regarding the herbal substance(s)/preparation(s) including data on relevant constituents

Considerable research has been done on the metabolism of monoterpenes. After rapid dermal and/or oral absorption, liver P450 mono-oxygenases are involved in biotransformation. Subsequently, 60-80% of absorbed monoterpenes are excreted as glucuronides (Villar et al. 1994).

Cal and Krzyaniak (2006), Cal et al. (2006) and Cal (2008) studied the penetration behaviour of TTO and pure constituents using a flow-through diffusion cells, human skin preparations and in vivo human studies which represented infinitive dose and occlusive application conditions. TTO or pure terpene-4-ol caused a significant increase in the skin accumulation of terpene-4-ol in the hydrophilic skin layers (dermis and epidermis).

The process of terpene penetration into the skin and through the skin can be considered to be strongly dependent on the experimental model used (choice of membrane, hydration level and dose) and on the carrier for the penetrating terpene, while in vivo the effect of evaporation – shown to be 98% needs to be considered.

Human pharmacokinetic data are not available for tea tree oil. In vitro dermal penetration studies using human skin preparations indicate that dermal absorption of TTO components is relatively low, up 2-4% of applied dose and the main components observed to penetrate were terpene-4-ol and α- terpineol. As the components of TTO are semi-volatile, the majority of the applied dose evaporates from the surface of the skin (Cross et al. 2008).

4.2. Clinical Efficacy

Clinical trials have been performed to test the efficacy of topical TTO products for a range of conditions including acne, wound healing, mycosis (oral candidiasis, denture stomatitis, onychomycosis, tinea and tinea pedis), protozoan infections, herpes labialis, dandruff, tinea.

4.2.1. Dose response studies

Not applicable.

4.2.2. Clinical studies (case studies and clinical trials) Overview

Clinical studies on effects of TTO were conducted for the following indications (presented in


Supragingival plaque

Minor skin lesions


Clinical studies conducted with combinations containing TTO (presented in



Pediculosis Clinical studies conducted with TTO

Acne vulgaris

Bassett et al. 1990 and Enshaieh et al. 2007 conducted randomised controlled trials and reported on the use of TTO for the treatment of mild to moderate acne.

A comparative study of tea-tree oil versus benzoylperoxide in the treatment of acne (Bassett et al. 1990).

A single-blind, randomised clinical trial on 124 patients to evaluate the efficacy and skin tolerance of 5% TTO gel in the treatment of mild to moderate acne when compared with 5% benzoyl peroxide lotion was performed. The results of this study showed that both 5% tea-tree oil and 5% benzoyl peroxide had a significant effect in ameliorating the patients’ acne by reducing the number of inflamed and non-inflamed lesions (open and closed comedones), although the onset of action in the case of tea-tree oil was slower. Fewer side effects were experienced by patients treated with tea-tree oil (Bassett et al. 1990).

The efficacy of 5% topical TTO gel in mild to moderate acne vulgaris: A randomised, double-blind placebo-controlled study (Enshaieh et al. 2007).

One study has been conducted on the possible efficacy of TTO in treatment of the acne vulgaris. It was a randomised double-blind clinical trial performed in 60 patients with mild to moderate acne vulgaris. They were randomly divided into two groups and were treated with TTO gel 5% (n=30) or placebo (n=30). They were followed every 15 days for a period of 45 days. Response to treatment was evaluated by the total acne lesions counting and acne severity index (ASI). The data was analysed statistically using t-test and by SPSS program. There was a significant difference between TTO gel and placebo in the improvement of the total acne lesions counting and also regarding improvement of the ASI. In terms of total acne lesions counting and ASI, TTO gel was 3.55 times and 5.75 times more effective than placebo respectively. Side-effects with both groups were relatively similar and tolerable. The authors concluded that topical 5% TTO is an effective treatment for mild to moderate acne vulgaris (Enshaieh et al. 2007).

Assessor’s Comment: 5% TTO gel showed to ameliorate acne lesions in two studies.

Feinblatt 1960 reported on the use of TTO for the treatment of furunculosis (boils). Thirty five patients (26 males and 9 females) with furuncles located in various sites (18 in the neck, 8 on the back, 6 in the axilla areas, 1 on the scalp, 4 on the face and forehead, 4 on the forearm, 1 on the calf and 1 on the external ear) many of them at multiple sites were enrolled in the study. Ten patients were given expectant treatment and 25 were treated with TTO painting the surface over the furuncle freely with the oil two or three times daily, after thoroughly cleaning the site. Results showed that, of the 10 untreated controls, five of the boils were finally incised and in five cases the infected site of the furuncle was still apparent after eight days. In the 25 cases treated with TTO, only one boil required

incision and in 15 cases the infected site of the furuncle was removed completely in eight days. In six cases the infected site of the furuncle, while still present after eight days, was reduced more than one- half and in three cases the infected site was reduced less than half in eight days. As to local reactions, three patients complained of slight temporary stinging.

In the same paper Feinblatt (1960) described a typical case report of a male patient aged 40 under treatment for diabetes mellitus, who complained of recurrent boils. TTO was applied directly over a large boil (3 x 3 cm), swollen, reddened and painful boil on his neck two or three times daily after thorough cleansing. There was definite improvement within two days, most of the inflammation had disappeared after four days and the skin healed after eight days with no untoward effects or local reactions. The patient repeated the use of TTO whenever a new boil developed and every time the further boils development aborted. The Author concluded that, due to its high germicidal activity against Staphylococcus aureus and on the basis of rapid healing without scarring achieved in the study, TTO may be used as an alternative option before surgical intervention in furunculosis.

Wound healing

Uncontrolled, open-label, pilot study of TTO solution in the decolonisation of MRSA positive wounds and its influence on wound healing (Carson et al. 2010, Edmondson et al. 2011).

The primary aim of an uncontrolled case series study was to assess whether a TTO solution used in a wound cleansing procedure could decolonise MRSA from acute and chronic wounds of mixed aetiology. The secondary aim was to determine if the TTO solution influenced wound healing outcomes. The product used was a water-miscible 10% v/v TTO solution. Nineteen participants with wounds suspected of being colonised with MRSA were enrolled in a pilot study. Seven were subsequently shown not to have MRSA and were withdrawn from the study. As many as 11 of the remaining 12 participants were treated with a wash solution of 3.3% TTO manually shaken in water; the solution was applied as part of the wound cleansing regimen at each dressing change. Dressing changes were three times per week or daily as deemed necessary by the study nurse following assessment. One participant withdrew from the study before treatment. No participants were MRSA negative after treatment. After treatment had been implemented, 8 out of the 11 treated wounds had begun to heal and reduced in size as measured by computer planimetry. TTO did not appear to inhibit healing and the majority of wounds reduced in size after treatment.

Two adverse events of pain were reported by participants who experienced pain during the cleansing procedure that may or may not have been because of the irrigation with the TTO solution (Edmondson et al. 2011).

Assessor’s comment: this study shows that treatment with TTO can influence positively wound healing through its antimicrobial activity; limit of the study is the small number of participants.

The Effect of Tea Tree Oil (Melaleuca alternifolia) on Wound Healing Using a Dressing Model (Chin & Cordell 2013)

A quasi-experimental study with 10 volunteers, who had wounds assumed to be infected with Staphylococcus aureus, were carried out to replicate in humans a 2004 in vitro study that used the same dressing model over Petri dishes to determine the antimicrobial effects of the fumes of TTO. Four of the 10 patients were used as matched participants to compare wound healing times between conventional treatment alone and conventional treatment plus fumes of TTO. The results demonstrated decreased healing time in all but one of the participants treated with TTO. However the study has several limitations: the small number of patients, whose characteristics were not compared with patients who did not volunteered and whose abscessed lesions were not all cultured to identify the offending micro-organism; moreover the type of antibiotics used concomitantly by the participants was

not controlled as well as other variables such as the age and the immune system function (Chin & Cordell 2013).

An Integrated Approach to Methicillin-resistant Staphylococcus aureus Control in a Rural, Regional- Referral Health care setting (Bowler et al. 2010).

A study was performed in a regional-referral hospital, 5 affiliated nursing homes and an outpatient MRSA clinic, in order to identify methods that could be applied in other resource-limited healthcare setting to decrease the prevalence and nosocomial transmission of MRSA.

Residents of the 5 nursing homes were screened for MRSA at baseline and 1 year later to detect the microbial quality improvement. Active surveillance cultures were performed on subsequently admitted nursing home residents, “high-risk” patients admitted to the hospital, and household contacts of clinic patients. The initial phase of decolonization consisted of systemic therapy with minocycline and rifampin and topical therapy with nasal mupirocin ointment and a bath or shower with 5% TTO body wash once per day for 7 days. During the following 5 months only 2% mupirocin nasal ointment two times daily and at least one TTO body wash once per day was applied for the first 5 days of each month. Three separate samples for cultures to document clearance of MRSA colonization were obtained at 1-week intervals 1 month after the completion of decolonization therapy. Samples for follow-up cultures were obtained at month 6 and month 12 after the completion of decolonization therapy. After intervention and follow-up for 12 months or more, the prevalence of MRSA carriage at the nursing homes decreased by 67% (P <0.001), and 120 (82%) of 147 nursing home residents and 111 (89%) of 125 clinic patients remained culture-negative for MRSA. Twenty-three (24%) of 95 new clinic patients had at least 1 MRSA-positive contact. Mupirocin resistance did not develop. In the hospital, the incidence rate of nosocomial MRSA infection decreased from 0.64 infections per 1,000 patient-days before the interventions to 0.40 infections per 1,000 patient-days 1 year after the interventions and to 0.32 infections per 1,000 patient-days 2 years after the intervention (P <0.01).

The author concluded that the use of active surveillance cultures and decolonization therapy was effective in decreasing the prevalence of asymptomatic carriage, the incidence of nosocomial infection, and the overall prevalence of MRSA. However it has to be noted that the number of patients lost to the follow-up was high (105 out of 272 patients who underwent decolonization in the nursing homes and in the MRSA clinic) (Bowler et al. 2010).

Chronic Wound Treatment with Topical Tea Tree Oil (Culliton & Halcon 2011)

A case study has been reported on the healing of a chronic lower-extremity wound in an 85-years old and more than 70 years smoker man using on a daily basis an impregnated dressing of 10% TTO in pumpkin seed oil after rinsing the wound. Even though the likelihood of the wound healing was minimal, it is not known whether the wound would have healed without the treatment and the role of pumpkin seed oil in the healing process. The author suggests that this approach could be explored in further studies as a wound treatment of diabetic patients with non-healing foot ulcers (Culliton & Halcon 2011).

Protozoan infections

A clinical investigation to determine the efficacy and safety of TTO use for vaginal douche and topical application in the treatment of trichomonal vaginitis, Candida albicans vaginitis and other vaginal infections was performed. The medication studied was a special emulsified 40% solution of Australian TTO with isopropropyl alcohol 13%. Hundred thirty cases of vaginal infections were investigated: trichomonal vaginitis (n=96), Candida albicans vaginitis (n=4), nulliparous cervicitis from Trichomonas vaginalis (n=20), chronic endocervicitis (n=10). Australian TTO was found to be highly effective in

treatment of tricomonal vaginitis, Candida albicans vaginitis, cervicitis and chronic endocervicitis (Peña 1962).


Onychomycosis is a superficial fungal infection that destroys the entire nail unit. It is the most frequent cause of nail disease, ranging from 2% to 13%. Standard treatments include debridement, topical medications, and systemic therapies.

Comparison of two topical preparations for the treatment of onychomycosis: TTO and clotrimazole (Buck et al. 1994).

A double-blind, multicenter, randomised controlled trial was performed at two primary care health and residency training centres and one private podiatrist’s office to assess efficacy and tolerability of topical application of 1% clotrimazole solution compared with that of 100% TTO for the treatment of toenail onychomycosis.

The participants included 117 patients with distal subungual onychomycosis proven by culture. Patients received twice-daily application of either 1% clotrimazole solution (n=53) or 100% TTO oil (n=64) for 6 months. Debridement and clinical assessment were performed at 0, 1, 3, and 6 months. Cultures were obtained at 0 and 6 months. Each patient’s subjective assessment was also obtained 3 months after the conclusion of therapy. Adverse reactions were erythema, irritation and oedema (7.8% in TTO and 5.7% in clotrimazole group), which cause the dropping out of four (3%) of the initial participants.

The baseline characteristics of the treatment groups did not differ significantly. After 6 months of therapy, the two treatment groups were comparable based on culture cure (clotrimazole = 11%, TTO = 18%) and clinical assessment documenting partial or full resolution (clotrimazole = 61%, TTO = 60%). Three months later, about one half of each group reported continued improvement or resolution (clotrimazole = 55%; TTO = 56%).

Topical therapy, including the two preparations presented in this paper, provide improvement in nail appearance and symptomatology. The study shows that use of a topical preparation in conjunction with debridement is an appropriate initial treatment strategy (Buck et al. 1994).

Assessor’s comment: the study shows efficacy of 100% TTO solution comparable to clotrimazole in the treatment of onychomycosis.

Syed et al. 1999 conducted a double blind randomised controlled trial investigating the treatment of onychomycosis. 40 patients were randomly allocated to the Treatment group of 2% butenafine hydrochloride and 5% TTO and 20 patients were randomly allocated to the control group consisting of a TTO cream of unspecified concentration. After 16 weeks of topical application three times daily and covering with an occlusive plastic dressing, 80% in the treatment group were cured and no patients in the control group were cured. TTO in the control cream did not show the expected response and TTO was mixed with butenafine hydrochloride in the treatment group, it is difficult to determine whether the TTO produced any effect in this group. Treatment in the control group was discontinued after 8 weeks so it is possible that the control treatment did not have sufficient time to render its full potency.

Oropharyngeal candidiasis. Oropharyngeal candidiasis is the most common opportunistic infection observed in the patients with HIV/AIDS.

Efficacy of melaleuca oral solution for the treatment of fluconazole refractory oral candidiasis in AIDS patients (Jandourek et al. 1998, Vazquez & Zawawi 2002).

Efficacy of Melaleuca oral solution, an USA branded non-prescription commercial mouthwash, in AIDS patients with fluconazole-resistant oropharyngeal Candida infections was investigated in two studies.

A prospective, single centre, open-labelled study was performed on thirteen patients with AIDS and oral candidiasis documented to be clinically refractory to fluconazole, as defined by failure to respond to a minimum of 14 days of > or = 400 mg fluconazole per day. Additionally, patients had in in vitro resistance to fluconazole, defined by minimal inhibitory concentrations of > or = 20 µg/ml.

Patients were given 15 ml Melaleuca oral solution four times daily to swish and expel for 2-4 weeks.

Resolution of clinical lesions of oral pseudomembranous candidiasis lesions evaluations were performed weekly for 4 weeks and at the end of therapy for clinical signs of oral candidiasis. Quantitative yeast cultures were performed at each evaluation.

A total of 13 patients were entered into the study, 12 were evaluable. At the 2-week evaluation, 7 out of 12 patients had improved, none were cured, and 6 were unchanged. At the 4-week evaluation, 8 out of 12 patients showed a response (2 cured, 6 improved), 4 were non-responders, and 1 had deteriorated. A mycological response was seen in 7 out of 12 patients. A follow-up evaluation 2-4 weeks after therapy was discontinued revealed that there were no clinical relapses in the 2 patients who were cured.

The authors concluded that melaleuca oral solution appeared to be effective as an alternative regimen for AIDS patients with oropharyngeal candidiasis refractory to fluconazole (Jandourek et al. 1998).

The efficacy of alcohol-based and alcohol-free USA branded non-prescription commercial mouthwashes containing TTO in patients with AIDS and fluconazole-refractory oropharyngeal candidiasis was investigated.

The prospective, single-centre, open-label study was performed in a university-based inner city HIV/AIDS clinic. The study included 27 patients with AIDS and oral candidiasis clinically refractory to fluconazole. Patients were randomised 1:1 to receive either alcohol-based or alcohol-free TTO mouthwash four times daily for 2–4 weeks. Thirteen patients were enrolled into cohort called 1, and treated with 15 ml of an alcohol-based TTO mouthwash 4 times daily for 2 weeks; 14 patients were enrolled into cohort called 2 and treated with 5 ml of an alcohol-free TTO mouthwash 4 times daily for 2 weeks. The different amount of mouthwash used in the two groups was due to need to use an equivalent quantity of TTO because the alcohol-based mouthwash was less concentrated than the non- alcohol-based mouthwash. Additional 2 weeks of therapy were provided for patients who showed clinical improvement but who had not demonstrated a complete clinical response at the end of the initial 2 weeks. The main outcome measure was resolution of clinical lesions of oral candidiasis. Evaluations were performed at 2 and 4 weeks for clinical signs and symptoms of oral candidiasis and quantitative yeast cultures.

All Candida albicans isolates showed some degree of in in vitro resistance to fluconazole. Overall, using a modified intent-to-treat analysis, 60% of patients demonstrated a clinical response to the TTO mouthwash (7 patients cured and 8 patients clinically improved) at the 4-week evaluation.

The authors concluded that both formulations of the TTO mouthwash appeared to be effective alternative regimens for patients with AIDS suffering from oropharyngeal candidiasis refractory to fluconazole (Vazquez & Zawawi 2002).

Assessor’s comment: These studies show a positive effect of TTO commercial preparations in patients with AIDS affected by oropharyngeal candidiasis. No information on the concentration of TTO in the preparations used in the studies is available. Moreover the studies were conducted on a small number of patients.

Denture stomatitis

In vitro and in vivo activity of Melaleuca alternifolia mixed with tissue conditioner on Candida albicans

(Catalán et al. 2008).

Denture stomatitis is an inflammatory reaction of the palatal and alveolar mucosa underlying removable dental prostheses. Denture stomatitis is more commonly seen in the maxillary mucosa than in the mandibular mucosa.

A study was performed to identify in vitro and in vivo activity of TTO mixed with different tissue conditioners on the Candida albicans strain. Microbiological tests were used to isolate Candida albicans from patients with denture stomatitis. The in vitro antifungal activity of TTO against Candida albicans was determined when it was applied directly and when it was mixed with tissue conditioners (Fitt, Lynal, Coe-Comfort). For the in vivo activity the responses of 27 denture stomatitis patients divided in three arms (each of them with 9 patients) were evaluated over a period of 12 days: the control group received Coe-Comfort tissue conditioner, treatment group 1 received 1 ml TTO mixed with 4 ml Coe- Comfort and treatment 2 group received 2 ml Nystatin mixed with 3 ml Coe-Comfort.

In the in vitro study, Coe-Comfort or Fitt conditioners mixed with 1 ml, 20% (v/v) of TTO exhibited a total inhibition of Candida albicans. Patients treated with TTO mixed with Coe-Comfort showed a significant decrease in palatal inflammation compared with those treated with Coe-Comfort (P = 0.001). In addition, a significant inhibition of Candida albicans growth was observed with TTO mixed with Coe-Comfort compared with only Coe-Comfort (P = 0.000004). There was no difference between the treatment arms at day 12. The data did however suggest the decrease in Candida albicans was faster with Treatment 1 (TTO) than with Treatment 2 (Nystatin). Conclusions of authors were that TTO mixed with Coe-Comfort tissue conditioner is effective in treating denture stomatitis (Catálan et al. 2008).

Assessor’s comment: This study has been conducted on a small number of patients, but suggests that TTO can be useful as an adjuvant in the care of denture stomatitis.

Treatment of tinea pedis

Satchell et al. 2002a and Tong et al. 1992 conducted randomised controlled trials and reported on the use of TTO for the treatment of tinea pedis.

Treatment of interdigital tinea pedis with 25% and 50% TTO solution: A randomised, placebo- controlled, blinded study (Satchell et al. 2002a).

A randomised, controlled, double-blinded study to determine the efficacy and safety of 25% and 50% TTO in the treatment of interdigital tinea pedis was conducted. One hundred and fifty-eight patients with tinea pedis clinically and microscopy suggestive of a dermatophyte infection were randomised to receive either placebo, 25% or 50% TTO mixed in ethanol and polyethylene glycol solution. Patients applied the solution twice daily to affected areas for 4 weeks and were reviewed after 2 and 4 weeks of treatment. There was a marked clinical response seen in 68% of the 50% TTO group and 72% of the 25% TTO group, compared to 39% in the placebo group. Mycological cure was assessed by culture of skin scrapings taken at baseline and after 4 weeks of treatment. The mycological cure rate was 64% in the 50% TTO group and 55% in the 25% TTO group, compared to 31% in the placebo group. Four (3.8%) patients applying TTO (one in the 25% group and three in the 50%) developed moderate to severe dermatitis that improved quickly on stopping the study medication (Satchell et al. 2002a).

Assessor’s comment: This randomised, controlled, double-blinded study showing efficacy of 50% and 25% TTO versus placebo in the treatment of interdigital tinea pedis. The study indicates also the potential development of dermatitis during TTO treatment.

TTO in the treatment of tinea pedis (Tong et al. 1992).

One hundred and four patients completed a randomised, double-blind trial to evaluate the efficacy of 10% w/w TTO cream compared with 1% tolnaftate and placebo creams in the treatment of tinea pedis. Significantly more tolnaftate-treated patients (85%) than TTO (30%) and placebo-treated patients (21%) showed conversion to negative culture at the end of therapy (p < 0.001); there was no statistically significant difference between TTO and placebo groups. All three groups demonstrated improvement in clinical condition based on the four clinical parameters of scaling, inflammation, itching and burning. The TTO group (24/37) and the tolnaftate group (19/33) showed significant improvement in clinical condition when compared to the placebo group (14/34; p = 0.022 and p = 0.018 respectively). TTO cream (10% w/w) appears to reduce the symptomatology of tinea pedis as effectively as tolnaftate 1% but is no more effective than placebo in achieving a mycological cure (Tong et al. 1992).

Assessor’s comment: This RCT shows efficacy of cream containing 10% TTO in improving symptoms of tinea pedis but without significant effects against the basic cause of pathology.

Treatment of vaginal infections of Candida albicans with TTO (Belaiche 1985a).

A clinical study with TTO on 28 patients (average age 34), in full oestro-progestinic activity affected by vaginitis caused by Candida albicans was carried out. One vaginal capsule weighting 2 g and containing 0.2 grams of TTO was administered every night before sleeping for 90 days. Only one woman had felt vaginal burning at the end of the first week and she stopped the treatment. 23 out of 27 patients showed a complete cure with disappearance of burning and white discharge (leucorrhea). 4 of them had to continue the treatment due to the persistence of leucorrhea. Biological examinations showed the disappearance of Candida albicans in 21 patients (Belaiche 1985a).

Treatment of skin infections with TTO (Belaiche 1985b).

A clinical study with TTO was conducted in 27 patients affected by different dermatological disorders with the following results:

3 cases of intertrigo infected with Candida albicans: application of pure TTO for 6 weeks – 2 months showed positive effects.

4 cases of angular stomatitis infected with Candida albicans and streptococci: twice a day application of TTO was successful in 3 out of 4 patients.

2 cases of staphylococcal and streptococcal impetigo in children: twice a day application of TTO caused improvement in 10-15 hours.

6 cases of staphylococcal acne: local treatment determined amelioration of the lesions, without a complete healing, acting on the infection and not on the sebaceous glands activity.

11 cases of nail infections by Candida albicans: treatment with pure TTO twice a day for 3 months, was successful in 8 patients with the first positive result in the first week; no significant improvement in 3 patients.

1 case of pytiriasis versicolor [tinea versicolour caused by Malassezia and/or Trichophytum]: twice a day application of TTO controlled the event after 20 hours (Belaiche 1985b).

Australian TTO: a natural antiseptic fungicidal agent (Shemesh & Mayo 1991)

A clinical trial with Australian TTO was undertaken for the treatment of various dermatological disorders for six months in 50 patients. Several forms of TTO preparations were used: pure oil (100%), lozenges with 1% TTO plus 2.5 mg ground leaf; and a 5% cream. 50 patients were supplied TTO for a

period of 1 to 4 weeks, depending on the severity of the condition being treated. All patients who completed treatment were either cured, all showed remarkable improvement in their presenting condition. One patient stopped the treatment after one day because of mild erythematous skin sensitivity to the 100% TTO (Shemesh & Mayo 1991).

Recurrent herpes labialis

Use of deception to achieve double-blinding in a clinical trial of TTO for the treatment of recurrent herpes labialis (Carson et al. 2008).

In a randomised, placebo-controlled trial of TTO for the treatment of recurrent herpes labialis (RHL), or cold sores, deception was used to prevent volunteers from identifying their treatment allocation. Volunteers received placebo (n=102) or TTO (n=112) ointment in preparation for their next episode of RHL and were told, falsely, that the aroma of the ointments had been changed to prevent identification of the treatment group. At the trial’s end, of the volunteers who had used their ointment and presented for treatment assessment (n=100), approximately 50% correctly guessed their treatment allocation (P=0.774). Amongst volunteers that had not presented for treatment assessment (n=114), 12 volunteers did not provide blinding data and 46 did not open their tube. For the 56 volunteers who opened their tube, less than half of those receiving TTO (44.4%) and only a small proportion of those on placebo (17.2%) were able to correctly identify their treatment allocation. Among the volunteers that were not treated, the P-value was 0.083. This study showed that the ethical use of deception may provide effective blinding in challenging circumstances (Carson et al. 2008).


Antimicrobial activity of garlic, TTO, and chlorhexidine against oral microorganisms (Groppo et al. 2002).

Antimicrobial activities of TTO, garlic, and chlorhexidine solutions against oral microorganisms were compared in a five week study consisting of thirty subjects. The first week was considered baseline. All subjects used a control solution (second week), and were randomly divided into the three groups (third week): G1- 0.12% chlorhexidine in a vehicle solution; G2 – 2.5% solution of a garlic (Allium sativum L.) aqueous extract 1:1; and G3 – 0.2% TTO in vehicle solution and 0.5% Tween 80. Dishes containing blood agar and Mitis Salivarius Bacitracin agar (MSB) were inoculated with the subjects’ saliva (collected twice a week). Total microorganisms and mutans streptococci were counted in blood agar and MSB, respectively.

Chlorhexidine and garlic groups showed antimicrobial activity against mutans streptococci, but not against other oral microorganisms. The TTO group showed antimicrobial activity against mutans streptococci and other oral microorganisms. Maintenance of reduced levels of microorganisms was observed only for garlic and TTO during the two consecutive weeks (fourth and fifth). Unpleasant taste (chlorhexidine 40%, TTO 30%, garlic 100%), burning sensation (chlorhexidine 40%, TTO 60%, garlic 100%), bad breath (chlorhexidine 40%, TTO 20%, garlic 90%), and nausea (chlorhexidine 0%, TTO 10%, garlic 30%) were reported. The authors concluded that garlic and TTO might be an alternative to chlorhexidine (Groppo et al. 2002).

Supragingival plaque

Clinical and antibacterial effect of tea tree oil – a pilot study (Arweiler et al. 2000)

Arweiler et al. 2000 reported the results from a pilot, non-randomised study on the effect of TTO on supragingival plaque formation and vitality. The study was performed with eight patients, which after professional tooth cleaning were asked to refrain any mechanical cleaning and to rinse the mouth with placebo (water) for 1 week, with chlorhexidine 0.1% (positive control) in a second and 0.34% TTO

water solution with milk as emulsifier in a third test week. Every test week was followed by a 10-day washout in which normal tooth brushing with standard toothpaste was performed. The TTO reduced neither the plaque index nor the plaque area relative to the placebo although there was a reduction in the amount of vital bacteria compared to placebo. Chlorhexidine significantly reduced plaque area and vital bacteria compared to placebo and reduced plaque index.

The effects of a tea tree oil-containing gel on plaque and chronic gingivitis (Soukoulis & Hirsch 2004)

The use of TTO for oral conditions such severe gingivitis was studied in a double-blind, longitudinal, non-crossover trial with 49 medically fit non-smokers (24 males and 25 females) aged 18-60 years. Subjects were randomly assigned to three groups and given either 2.5% TTO-gel, 0.2% chlorhexidine gel, or a placebo gel to be applied with a toothbrush twice daily. Treatment effects were assessed using the Gingival Index (GI), Papillary Bleeding Index (PBI) and plaque staining score at four and eight weeks. The TTO group had significant reduction in PBI and GI scores. However, TTO did not reduce plaque scores, which tended to increase over the latter weeks of the study period. The Authors concluded that topical application of TTO gel to inflamed gingival tissue may be useful as an adjuvant of chemotherapeutic periodontal therapy.

Minor skin lesions

A randomised, controlled trial of TTO topical preparations versus a standard topical regimen for the clearance of MRSA colonisation (Dryden et al. 2004)

Two topical MRSA eradication regimes were compared in hospital patients: a standard treatment included mupirocin 2% nasal ointment, chlorhexidine gluconate 4% soap, silver sulfadiazine 1% cream versus a TTO regimen. The TTO regimen comprised TTO 10% cream applied to the anterior nostrils three times a day for five days; TTO 5% body wash all over the body at least once a day for five days; TTO 10% cream to skin lesions, wounds and ulcers, and also to axillae or groins as an alternative to the body wash. One hundred and fourteen patients received standard treatment and 56 (49%) were cleared of MRSA carriage. One hundred and ten received TTO regimen and 46 (41%) were cleared.

There was no significant difference between treatment regimens (Fisher’s exact test; P ¼ 0:0286).

Mupirocin was significantly more effective at clearing nasal carriage (78%) than TTO cream (47%; P ¼ 0:0001), but TTO treatment was more effective than chlorhexidine or silver sulfadiazine at clearing superficial skin sites and skin lesions. The TTO preparations were effective, safe and well tolerated and could be considered in regimens for eradication of MRSA carriage (Dryden et al. 2004).

Assessor’s comment: this study shows the efficacy of a cream containing TTO 10% to clean skin lesions, wounds and ulcers.

TTO as an alternative topical decolonisation agent for methicillin-resistant Staphylococcus aureus (Caelli et al. 2000)

Clearance of MRSA was also investigated by Caelli et al. 2000 who conducted a pilot randomised controlled trial on 30 hospital inpatients aged between 32 and 82 years. Fifteen patients were randomised to the TTO treatment group consisting of 4% TTO nasal ointment and 5% TTO body wash. Fifteen patients were randomised to the standard treatment group consisting of 2% mupirocin nasal ointment and triclosan body wash. The TTO treatment combination appeared to perform better than the standard treatment of mupirocin and triclosan although the difference was not statistically significant.

Assessor’s comment: this is a pilot study with a too small number of patients.


Treatment of dandruff with 5% TTO shampoo (Satchell et al. 2002b).

The efficacy and tolerability of 5% TTO on mild to moderate dandruff vs. placebo was investigated in a randomised, single-blind, parallel-group study. One hundred twenty-six male and female patients, aged 14 years and older, were randomly assigned to receive either 5% TTO shampoo or placebo, which was used daily for 4 weeks. The dandruff was scored on a quadrant-area-severity scale and by patient self-assessment scores of scaliness, itchiness, and greasiness. The 5% TTO shampoo group showed a 41% improvement in the quadrant-area-severity score compared with 11% in the placebo group (P < 0.001). Statistically significant improvements were also observed in the total area of involvement score, the total severity score, and the itchiness and greasiness components of the patients’ self-assessments. The scaliness component of patient self-assessment improved but was not statistically significant. There were no adverse effects. 5% TTO appears effective and well tolerated in the treatment of dandruff (Satchell et al. 2002b).

Assessor’s comment: this study shows efficacy and good tolerability of a 5% TTO shampoo in the treatment of dandruff.

Finally a case study describing a 5-day successful use of vaginal pessaries containing 200 mg of TTO in vegetable basis for the treatment of vaginal discharge typical of anaerobic vaginosis was reported by Blackwell 1991.

Clinical Treatment of Ocular Demodecosis by Lid Scrub With Tea Tree Oil (Gao et al. 2007)

Gao et al. 2007, following an in vitro observation that Demodex is resistant to a wide range of antiseptic solutions but susceptible to TTO in a dose-dependent manner, reported on the results of a retrospective review of an in vivo treatment with TTO of eleven patients with ocular Demodex. They found that Demodex count dropped to zero for two consecutive visits in less than four weeks in eight patients. Ten out of eleven patients showed different degrees of symptomatic relief and notable reduction of inflammatory signs. A significant visual improvement was noted in six out of twenty-two eyes which was associated with the development of a stable lipid tear film. The TTO lid scrub effectively eradicated ocular Demodex and resulted in subjective and objective improvements, which was interpreted a result in understanding , but caused notable irritation in 3 patients. Positive results were interpreted as preliminary results useful in understanding Demodex pathogenicity in causing several ocular surface diseases. Retrospective nature and the lack of using a standardized format to grade symptoms as well as randomisation with lid scrub using baby shampoo and small number of patients were recognised as a limitation of the value of this study (Gao et al. 2007).

Finally the results of a case study were described by Millar 2008 where 100% TTO was used for the topical treatment of multiple warts, due to human papilloma virus, on the hand of a seven year old girl. Salicylic acid (12%) and lactic acid (4%) was previously used on this condition but only resulted in the temporary removal of the warts and they recurred in greater numbers. After five days treatment with undiluted TTO, all warts were reduced in size. After a further 7 days, there was no evidence of warts and complete reepithelialisation of the area. No recurrence has been reported.

A summary of these studies is presented in Table 5.

Table 5: Clinical studies on humans Clinical studies conducted with combinations containing TTO


Treatment of toenail onychomycosis with 2% butenafine and 5% TTO in cream

The objective of a randomised, double-blind, placebo-controlled study was to examine the clinical efficacy and tolerability of 2% butenafine hydrochloride and 5% TTO incorporated in a cream to manage toenail onychomycosis in a cohort. Sixty outpatients (39 M, 21 F) aged 18–80 years (mean 29.6) with 6–36 months duration of disease were randomised to two groups (40 and 20), active and placebo. Patients were shown how to apply the trial medication at home three times a day topically for 7 days. After 16 weeks, 80% of patients using medicated cream were cured, as opposed to none in the placebo group. Four patients in the active treatment group experienced subjective mild inflammation without discontinuing treatment. During follow-up, no relapse occurred in cured patients and no improvement was seen in medication-resistant and placebo participants (Syed et al. 1999).

Assessor’s comment: this is randomised, double-blind, placebo-controlled study showing efficacy of a combination of TTO (5%) with 2% butenafine hydrochloride incorporated in a cream in management of toenail onychomycosis.


Reduction of Mouth Malodour and Volatile Sulphur Compounds in Intensive Care Patients using an Essential Oil Mouthwash

A study was carried out to explore the effect of an essential oil solution on levels of malodour and production of volatile sulphur compounds (VSC) in patients nursed in intensive care unit. Thirty two patients received 3 min of oral cleaning using an essential oil solution (mixture of TTO, peppermint, Mentha piperita and lemon, Citrus limon) on the first day, and benzydamine hydrochloride on the second day. Two trained nurses measured the level of malodour with a 10 cm visual analogue scale (VAS) and VSC with a Halimeter before (Pre), 5 min after (Post I) and 1 h following treatment (Post II). The level of oral malodour was significantly different following the essential oil session, and differed significantly between two sessions at Post I (p < 0.005) and Post II ( p < 0.001). Differences between the two sessions were significant (benzydamine hydrochloride, p < 0.001; essential oil, p < 0.001) in the level of VSC and significantly lower in the essential oil session than benzydamine hydrochloride at the Post II (p < 0.05). These findings suggest that mouth care using an essential oil mixture of diluted TTO, peppermint and lemon may be an effective method to reduce malodour and VSC in intensive care unit patients (Hur et al. 2007).

Assessor’s comment: These studies suggests that TTO, alone or in combination, probably due to its antimicrobial activity against oral microorganisms, can be useful to fight halitosis.

A Clinical Study: Melaleuca, Manuka, Calendula and Green Tea Mouth Rinse

A mouthwash (IND 61,164) containing essential oils and extracts from four plant species (Melaleuca alternifolia, Leptospermum scoparium, Calendula officinalis and Camellia sinensis) was tested. The study aimed to evaluate the safety, palatability and preliminary efficacy of the rinse. Fifteen subjects completed the Phase I safety study. Seventeen subjects completed the Phase II randomised placebo- controlled study. Plaque was collected, gingival and plaque indices were recorded (baseline, 6 weeks, and 12 weeks). The relative abundance of two periodontal pathogens (Actinobacillus actinomycetemcomitans, Tanerella forsythensis) was determined utilizing digoxigenin-labelled DNA probes. ANCOVA was used at the p = 0.05 level of significance. Two subjects reported a minor adverse event. One subject withdrew from the study. Several subjects objected to the taste of the test rinse

but continued treatment. Differences between gingival index, plaque index or relative abundance of either bacterial species did not reach statistical significance when comparing nine placebo subjects with eight test rinse subjects. Subjects exposed to the test rinse experienced no abnormal oral lesions, altered vital signs, changes in liver, kidney, or bone marrow function. The authors concluded that larger scale studies would be necessary to determine the efficacy and oral health benefits of the test rinse (Lauten et al. 2005).

Assessor’s comment: a preliminary study on a small number of patients showing positive effects of mouth rinse containing TTO in combination with Manuka, Calendula and Green Tea.


An ex vivo, assessor blind, randomised, parallel group, comparative efficacy trial of the ovicidal activity of three pediculicides after a single application – TTO and lavender oil, eucalyptus oil and lemon TTO, and a “suffocation” pediculicide

Components to the clinical efficacy of pediculicides are: (i) efficacy against the crawling stages (lousicidal efficacy); and (ii) efficacy against the eggs (ovicidal efficacy). Lousicidal efficacy and ovicidal efficacy are confounded in clinical trials. A trial was specially designed to rank the clinical ovicidal efficacy of pediculicides. Eggs were collected, pre-treatment and post-treatment, from subjects with different types of hair, different coloured hair and hair of different length.

Subjects with at least 20 live eggs of Pediculus capitis (head lice) were randomised to one of three treatment-groups: a TTO and lavender oil pediculicide (TTO/LO); an eucalyptus oil and lemon TTO pediculicide (EO/LTTO); or a “suffocation” pediculicide. Pre-treatment: 10 to 22 live eggs were taken from the head by cutting the single hair with the live egg attached, before the treatment (total of 1,062 eggs). Treatment: The subjects then received a single treatment of one of the three pediculicides, according to the manufacturers’ instructions. Post-treatment: 10 to 41 treated live eggs were taken from the head by cutting the single hair with the egg attached (total of 1,183 eggs). Eggs were incubated for 14 days. The proportion of eggs that had hatched after 14 days in the pre- treatment group was compared with the proportion of eggs that hatched in the post-treatment group. The primary outcome measure was % ovicidal efficacy for each of the three pediculicides.

Seven hundred twenty two subjects were examined for the presence of eggs of head lice. Ninety two of these subjects were recruited and randomly assigned to: the “suffocation” pediculicide (n = 31); the

TTO/LO (n = 31); and the EO/LTTO (n = 30 subjects). The group treated with EO/LTTO had an ovicidal efficacy of 3.3% (SD 16%) whereas the group treated with TTO/LO had an ovicidal efficacy of 44.4%

(SD 23%) and the group treated with the “suffocation” pediculicide had an ovicidal efficacy of 68.3% (SD 38%).

Ovicidal efficacy varied substantially among treatments, from 3.3% to 68.3%. The “suffocation” pediculicide (68.3% efficacy against eggs) and the TTO/LO (44.4% efficacy against eggs) were significantly more ovicidal than EO/LTTO (3.3%) (P < 0.0001). The “suffocation” pediculicide and TTO/LO are also highly efficacious against the crawling-stages. Thus, the “suffocation” pediculicide and TTO/LO should be recommended as first line treatments (Barker & Altman 2011).

Assessor’s comment: this study shows the efficacy of a combination of TTO with lavender oil as pediculicide.

4.3. Clinical studies in special populations (e.g. elderly and children)

No significant study has been performed in special populations.

Combination of Essential Oil of Melaleuca alternifolia and Iodine in the treatment of Molluscum Contagiosum in children.

A randomized double blinded placebo controlled three arm study, with intention to treat analysis, was performed in children for the treatment of molluscum contagiosum viral infection, which is a common benign childhood condition and is increasingly found as a sexual transmitted disease in adults. Fifty- three children (mean age 6.3+5.1 years) were randomised and treated with twice a day topical application of either a combination of 75% V/V TTO, canola oil and organically bound iodine in a proprietary formulation (TTO-I – 19 patients), TTO an canola oil in the same proportion (18 patients), or the same organically bound iodine alone in a vehicle of canola oil as control (I – 16 patients). The concentration of iodine both in the control preparation and in the TTO-I was 35 µmolar. The treatment consisted in the application of 4 µl medication on each molluscum lesion twice a day for 30 days or until all lesions had resolved, if this required less than 30 days, and was considered successful if lesions completely cleared or were reduced in number by greater than 90%. Forty-eight children were available for follow up at the end of 30 days, being lost 2 children in both the I and TTO group and 1 in the TTO-I group. Best results were shown in the TTO-I group were 11 children had total resolution and 5 had a reduction in the number of lesions greater than 90% with a total of 16 patients meeting the study criteria for the treatment success. In the TTO group 3 patients met the criteria and only 1 in the I group. Since adverse effect were limited to a small amount of redness around the base of some lesions, with no discontinued treatment due to adverse reaction, results of the study suggest a synergistic safe use of TTO and organically bound iodine in the treatment of molluscum contagiosum (Markum & Baillie 2012).

4.4. Overall conclusions on clinical pharmacology and efficacy

TTO has been widely investigated in several clinical studies, which showed its efficacy as an antiseptic in various conditions.

Two RCT conducted in different countries support the ability of a 5% TTO gel to ameliorate lesions in the treatment of mild to moderate acne vulgaris (Enshaieh et al. 2007, Bassett et al. 1990). Another study conducted by Feinblatt (1960) is insufficient to show the efficacy of 100% TTO for the treatment of furunculosis (boils) despite the positive findings.

Clinical trials support the efficacy versus placebo of 50% and 25% TTO solutions in the treatment of interdigital tinea pedis (Satchell et al. 2002a) and the traditional use of a cream containing 10% TTO to improve symptoms of tinea pedis, but with no significant effects against the basic cause of the pathology (Tong et al. 1992).

A RCT showed that 100% TTO has an effect comparable to that of clotrimazole for the treatment of onychomycosis (Buck et al. 1994). Another RCT (Syed et al. 1999) did not show effects of TTO in onychomycosis, but information are lacking on the TTO concentration of the cream used in the study.

The use of TTO for the reduction of yeast and fungal infections was studied in various clinical trials conducted by different investigators, but in some studies information on the TTO content of the preparation used is not provided (Jandourek et al. 1998, Vazquez & Zawawi 2002) and in the other studies the number of patients or the study design cannot be considered supportive for the well- established use (Catalán et al. 2008, Belaiche 1985a, Belaiche 1985b).

Two RCT (Dryden 2004, Caelli et al. 2000) and one open controlled pilot study (Enshaieh et al. 2007, Bassett et al. 1990) conducted by different investigators showed that different concentrations (3.3- 10%) of TTO may influence positively wound healing through its antimicrobial activity and clearance of MRSA.

Clinical studies for the relief of the symptoms associated with a variety of oral cavity diseases or for the prevention of dental plaque growth support the use and antimicrobial activity of various TTO preparations (TTO commercial oral solutions, 6% TTO in aqueous gel, 0.34% TTO dispersed in milk and diluted with water, 2.5% TTO gel) but they were performed in a too small number of patients or showed no significant results (Jandourek et al. 1998, Vazquez & Zawawi 2002, Catálan et al. 2008, Groppo et al. 2002, Arweiler et al. 2000, Soukoulis & Hirsch 2004).

The clinical study on the use of TTO for the treatment of ocular Demodex (Gao et al. 2007) provides an interesting hypotesis for further investigation.

Clinical investigations on the use in vaginitis, cervicitis and endocervicitis gives only a very low level of evidence, insufficient to support the use of any formulation tested (Peña 1962, Blackwell 1991, Belaiche 1985a).

5. Clinical Safety/Pharmacovigilance

5.1. Overview of toxicological/safety data from clinical trials in humans

Most of the clinical studies in which skin irritations and allergies were demonstrated utilized 1% TTO preparations thus indicating that commonly used topical concentrations are likely to elicit allergic responses in susceptible individuals. Because of demonstrated systemic toxic effects, TTO should never be used internally. In 2005, Nielsen reviewed the reported toxicity of TTO and its major components and derived an estimated NOAEL for whole TTO of 330 mg/kg b.w. based on component data with a worst case scenario of 117 mg/kg b.w. (Nielsen 2005).

Skin Irritation

In a recent review, Hammer et al. (2006) reported the results of a number of publications on human patch testing with TTO. The results of these studies are summarised in the Table 6. Undiluted TTO has been reported to cause skin irritation in a small proportion of subjects (generally <5%). The irritation potential of TTO may be related to the age of the oil, with aged oils (presumably containing higher levels of peroxides and degradation products such as ascaridol) displaying a greater incidence of irritation.

Table 6: Skin irritation potential of TTO in humans


Greig et al. (2002) investigated the allergic reaction threshold using occluded patch testing in eight subjects previously confirmed to be sensitised to TTO. The reaction threshold concentrations for TTO were highly variable and were found to occur at 0.5% in one subject, while still being somewhat doubtful at 10% in one other subject. The lowest concentration able to induce a level 1-3 response in the other volunteers fell between these: 1% (one person), 2% (three people) and 5% (two people). In the same subjects, 11 individual components of TTO were also tested. The TTO components that caused reactions in pre-sensitised individuals were p-cymene, terpinolene, α-terpinene and γ- terpinene. The authors commented that they had concerns that the oil samples may have become oxidised within the duration of the study.


The elicitation studies generally demonstrate that the threshold for elicitation of allergic reactions in subjects sensitised to tea tree are >2% in the majority of sensitised subjects. Friedman & Moss (1985) suggested that when induction conditions are severe then the elicitation threshold is low. When induction occurs under mild conditions (as is the case with TTO) much higher exposures are required to elicit an allergic reaction and allergic reaction may not occur as long as exposure remains low.


A test on human volunteers using a low dose but highly maximized conditions failed to produce sensitisation reactions. A Kligman Human Maximization test was conducted on 1% TTO in petrolatum in 22 healthy male and female volunteers. The test material was applied under occlusion to the same site on the volar forearm of all subjects for 5 alternate-day 48-hour periods. The patch site was pre- treated for 24 hours with 5% aqueous SLS under occlusion for the initial patch only. Following a 10-14 day rest period, a challenge patch of the test material was applied to a fresh site for a 48-hour period under occlusion. Prior to challenge, 5% SLS was applied to the test site for 30 minutes under occlusion on the left side of the back whereas the test materials were applied without SLS treatment on the right side. A fifth site challenged with petrolatum served as a control (RIFM 1802).

Clinical Diagnostic Studies

Two cases of contact dermatitis associated with the application of TTO have been reported by Apted (1991). The use of a vehicle and other aspects of the patch testing were not discussed however, positive patch tests were apparently obtained.

A TTO hand-wash was provided for staff in the intensive care unit of a major hospital. A 45-year-old nurse developed raised red lesions at sites of contact within 5 min of application. This reaction occurred on 3 separate occasions, the lesions persisting for at least 36 h. Previously, she had regularly used a shampoo containing TTO at home without adverse effects. Patch testing was performed (using IQ chambers) on 3 separate occasions over several months, firstly on the outer upper arm and then on the upper back. There was no response to 10 different samples of 10% TTO tested at 10%. When the

TTO used in the manufacture of the handwash was tested at the concentration in the product (3%) there was no reaction. When tested at 100% however, the 10 samples of TTO produced reactions on 2 occasions. Mild erythema and pruritus also occurred with 6 of the 10 oils on 1 occasion and with 4 on the other. On the 2nd occasion, one oil caused erythema and oedema. She also gave vesicular responses to 3 metals (potassium dichromate, cobalt chloride, and nickel sulfate) (Greig et al. 1999).

Two professional aroma therapists with suspected allergic contact dermatitis after having handled a variety of essential oils in the course of their work were patch tested with a total of 60 and 22 oils, respectively. Occluded patches with the oils including TTO at 2% diluted in white petrolatum, were applied for 48 hours. In one of these patients a positive (+++) reaction was observed to this oil. It is not clear how many other oils produced positive reactions in this patient (Dharmagunawardena et al. 2002).

A 46-yr-old man applied pure TTO to a superficial abrasion on his left leg. Within a few days, the treated area became red and itchy. Applications of TTO were stopped, but the eruption became generalized, with urticarial plaques and atypical targets. A skin biopsy from a target-like lesion showed a spongiotic dermatitis. The patient then developed dermatitis under an Elastoplast® dressing used on the biopsy site. The lesions cleared with oral prednisone. Five months later, patch tests were done with the North American standard series and with TTO, hydroabietyl alcohol, abietic acid and turpentine peroxides. The patient was also tested to a drop of his own, old TTO. At day 4, the patient reacted to both TTO samples, with a stronger reaction to his own than to the fresh preparation. Positive reactions to colophony, hydroabietyl alcohol and Balsam of Peru were also noted (Khanna et al. 2000).

Open and closed tests on TTO at different concentrations in water were conducted on a 74-year-old man after the occurrence of blistering dermatitis from the use of a TTO containing wart paint. The patient reacted to a concentration of 1% at the closed site and at 100% at the open site. No effects were seen in 50 controls at 1% or 5% (Bhushan & Beck 1997).

A 64 year old woman with severe eczema of the ears, neck and upper chest following the use of Earex® ear drops was patch tested with the European standard, preservatives, cosmetics and the hairdressing series as well as her own products including Earex® ear drops which was positive. Further testing to the ingredients of Earex drops was conducted including 5% TTO to which she reacted. No further details provided (Stevenson & Finch 2003).

Tests were conducted on a 33-year-old woman after the occurrence of dermatitis from the use of undiluted TTO. Finn chambers and Scanpor tape were used. Reactions were assessed day 3. A positive reaction was observed (Selvaag et al. 1994).

In a study on the frequency of sensitisation to TTO in consecutive patients, patch tests were conducted in 10 dermatological departments. TTO gave positive reactions in 16/794 patients when tested at 5% in diethylphthalate. Of these 16 reacting patients, 12/16 pts had used TTO in the past, mainly as a treatment for herpes simplex, eczema and onychomycosis. 4/16 subjects denied any contact to TTO. 7/16 subjects also showed a positive patch test to oil of turpentine at 10% in petrolatum (Treudler et al. 2000).

A crystalline compound was isolated from oxidized TTO identified as 1,2,4-trihydroxymenthane by mass spectroscopy. Fifteen patients sensitive to TTO were tested epicutaneously with seven typical constituents of and two degradation products of TTO. Positive effects, 1,2,4-trihydroxymenthane was shown to be an important allergen as well as ascaridol, another degradation product of TTO. Besides 1,2,4-trihydroxymenthane and ascaridol, alpha-phellandrene, alpha-terpinene, and terpinolene were found to give positive reactions as well. The authors noted that TTO kept under practical daily conditions undergoes photo-oxidation within a short time, leading to the formation of peroxides and subsequently to the generation of degradation products. Compounds like ascaridol and 1,2,4-

trihydroxymenthane are formed. These degradation products are moderate to strong sensitizers and must be considered responsible for the induction of contact allergy developing in individuals having treated themselves with TTO (Harkenthal et al. 2000).

Seven male and female patients who had become sensitised to TTO were examined during a 3-year period in an outpatient dermatology clinic. They had been treating pre-existing skin conditions, which included foot fungus, dog scratches, “pimples” of the legs, insect bites and hand rashes. All patients initially had an eczematous dermatitis consisting of ill-defined plaques of erythema, oedema and scaling. In 3 patients vesciculation was also present. The patients were patch tested on their upper backs with Finn Chambers to a 1% solution TTO and solutions of 11 constituent compounds. The application time was 48 hours. Reactions were assessed at 50 hours. Control patches of ethanol, olive oil and a blank Finn Chamber were also applied. A total of 20 control patients with unrelated dermatoses were patch tested to the 1% TTO solution and 10 control patients were patch tested to solutions of 11 constituent compounds. 7 control patients were patch tested to the higher concentrations of the constituent compounds. The patch test vehicle was ethyl alcohol in all cases. All seven patients reacted to TTO at 1%. No effects were seen in 20 control subjects. Positive reactions were also seen with d-limonene, α-terpinene, aromadendrene, terpinen-4-ol, α-phellandrene, p- cymene, α-pinene and terpinolene (Knight & Hausen 1994).

Human Patch Tests

There are several human patch test studies with TTO reported in the literature. These have been summarised in Table 7. In total, patch tests have identified 151 subjects with positive reactions to TTO among 9367 subjects. The rate of allergic reactions varies from one study to another and is between 0.6% and 2.4% (mean 1.6%). The incidence and strength of the reactions was generally higher with oxidised TTO samples. Rutherford et al. (2007) concluded that oxidised TTO has a sensitising capacity three times stronger than fresh TTO. This is consistent with the finding of Hausen (Hausen et al 1999, Hausen 2004) and the relatively high rate of positive reactions observed in patch testing of a deliberately oxidised TTO sample (Coutts et al. 2002).

Nielsen (2005) concluded that the prevalence of positive findings following exposure of pre-sensitised dermatological patients in the clinical studies to TTO is generally around 0.4%-0.6% (Hammer et al. 2006). Thus, TTO has only a weak sensitising potential among pre-sensitised people, though the present known number may be an overestimate due to problems with aged TTO (unknown peroxide levels) and selection bias in some clinical studies.

While patch testing remains a useful diagnostic tool used by Dermatologists, it has some well recognised limitations. In most studies the researchers neglect to demonstrate clinical relevance of any positive patch testing results (Lachapelle 1997). Rutherford et al. (2007) observed positive patch tests with TTO in 41 out of 2320 patients. However when the patients were questioned regarding prior exposure to TTO products, only 17 out of 41 reactions were of possible clinical relevance, but none could be demonstrated to have probable or definite relevance. In other words, out of the 41 patients giving a positive patch test to TTO, 24 subjects had no identified prior exposure to TTO.

False positives in the patch tests are not uncommon. False positives can occur as a result of irritancy rather than a true allergic response, particularly as TTO can cause skin irritation both in animals (Beckmann & Ippen 1998) and humans (Aspres & Freeman 2003). Similarly, false positives may result from cross-reactions where patients react to a substance which is not the substance which initially induced the allergic state. TTO is an essential oil with components that are also found in other natural substances. The phenomenon of “excited skin syndrome” has also been suggested to contribute to false positives (Maibach In Ring & Burg 1981). This phenomenon occurs when a subject shows multiple positive patch tests which cannot be reproduced when the subject is retested.

It should also be noted that many of the Dermatological units obtain their samples of TTO from Chemotechnique Diagnostics have confirmed that their oil has been deliberately oxidised.

Table 7: Summary of human patch test studies

TTO may be regarded as only a weak allergen, where it has any sensitising potential. Thus, normal in- use exposure may induce a sub-clinical allergic state which will not be elicited under normal exposure conditions but may become apparent only under occlusive patch test conditions. This is supported by the absence of any clearly documented epidemic of consumer complaints associated with TTO containing cosmetic products. This hypothesis has been proposed to explain some of the allergic responses seen in clinical studies for some fragrance ingredients (Hostynek & Maibach 2004). Furthermore, the relatively high volatility of TTO and the low dermal penetration may also explain the difference in the result obtained with diagnostic patch testing, where the dermal penetration is expected to be increased due to occlusion, and the lack of consumer complaints as demonstrated by company data.

5.2. Patient exposure

Aside from market presence and data from studies (see section 4), there are no concrete data concerning patient exposure.

5.3. Adverse events and serious adverse events and deaths

According to the data provided by ATTIA Ltd., since record keeping commenced in 1987, 23 adverse events for TTO have been recorded in Australia, corresponding to 0.8 incidents per year. As the estimated sale from 1987 is 25 million unit of bottle containing 100% TTO, the incidence appear

extremely low. Of the 23 events reported, 6 are of identified 100% TTO, 10 product are related to formulated product of less than 100% concentration of TTO, 7 are unidentified, no concentration is reported, but TTO is ‘suspected’.

Cutaneous and mucosal reactions

Adverse skin reactions like smarting pain, itch, and allergic reactions have been reported. The frequency is not known (Swedish leaflet).

Burn-like skin reactions have been reported in Denmark. The frequency is rare (<1/1000).

It is likely that the irritation potential of tea tree oil may be related to the age of the oil, with aged oils (presumably containing higher levels of peroxides and degradation products such as ascaridol) displaying a greater incidence of irritation (Australian Government – Rural Industries Research and Development Corporation 2007).

Allergic reactions

Allergic skin reactions reported in Denmark are not common (≥1/1.000 and < 1/100).

Forty-six cases of allergic contact dermatitis with the use of TTO have been reported in the literature from 1991 to 2004, mostly limited to mild symptoms, such as erythema and pruritus, or eczematous plaque in the area of application; however bullous and erythema multiforme-like reactions have also been reported and, in one particular case of a 18 year female patient, linear Immunoglobulin A (IgA) disease appears to have been precipitated (Perrett et al. 2003, Crawford et al. 2004). Manifestation and location depend on the site of the application, duration of exposure and severity of the host immunological response (Crawford et al. 2004).

For example Varma et al. reported a case of vaginal application of TTO and lavender oil in a patient with concurrent severe eczema (Halcón & Milkus 2004). Bhushan & Beck (1997) reported a case of blistering dermatitis where a wart paint containing TTO had been used for a period of 4 months. The man had a positive patch test to 1% TTO, while 50 controls were negative on testing with 1% and 5% aqueous tea tree solutions. The case patient was treated with topical corticosteroids and recovered with no known sequelae (Halcón & Milkus 2004).

At the Skin and Cancer Foundation (Sydney, NSW, Australia), three of 28 normal volunteers tested strongly positive to patch testing with 25% TTO. Following further patch testing with TTO constituents, all three patients reacted strongly to two preparations containing sesquiterpenoid fractions of the oil, which supports the indication that sesquiterpenes hydrocarbons may be potent allergens and that the allergenic fraction may be reduced by removal of sesquiterpenes by fractionation and selection of genotypes with lower sesquiterpene contents. These adverse skin reactions were classified as allergic reactions rather than irritant, because erithema with market dermal oedema and itching appeared in the absence of the epidermal reaction usually seen in an irritant patch test reaction, where scaling and wrinkling of epidermis is evident (Rubel et al. 1998). Due to the widespread use of TTO, especially in Australia, prevalence rate for allergic contact dermatitis reactions are difficult to estimate and it seems that in Australia the prevalence is higher than in other Countries, such as for instance United States, due to the previous exposure to TTO (Crawford et al. 2004).

In the evaluation of patients with allergy to TTO it should be considered that they could have been exposed to several other essential oils with common chemical constituents known to be sensitizers (Crawford et al. 2004). Moreover, whereas fresh TTO seems to possess only a weak sensitizing potential, it is well known that oxidized constituents of TTO increase their ability to act as allergens (Harkenthal et al. 2000, Carson & Riley 2001, Norwegian Food Safety Authority 2012).In ten separate human patch test studies involving almost 9400 people, an average of 1.6 per cent of people showed some allergic reaction to TTO. It is known, however, that in several of the patch test studies degraded

tea tree oil was used to test for sensitisation. The incidence of sensitisation in the patch test studies may therefore be an overestimate due to peroxides and their degradation products in the oils tested (Australian Government – Rural Industries Research and Development Corporation 2007).

The studies generally have demonstrated that the TTO concentration at which an allergic response may be elicited is greater than 2% in the majority of sensitised subjects. Data collected by six companies that supply TTO products shows that the incidence of adverse reports is dependent on the concentration of oil, with most of the reports occurring with undiluted TTO. Overall, with records from more than 10 years covering 38 million products – many of which were full strength or high concentration tea tree oil, the incidence of adverse events reported for all tea tree oil-containing products is low (0.0016%) (Australian Government – Rural Industries Research and Development Corporation 2007.

Acute intoxications

Several cases of human TTO poisoning have been reported, mostly involving the ingestion of modest volumes (N 10-25 ml) of oil. In two cases, ingestion of TTO resulted in what appeared to be systemic contact dermatitis (Carson & Riley 1998).

It has been reported the case of a patient comatose for the first 12 h and then semi-conscious for the following 36 h after ingestion of approximately half a cup of TTO. Other cases reported that two children who ingested less than 10 ml TTO became ataxic and drowsy or disorientated. Both were treated supportively and recovered fully without further complications (Carson & Riley 1998).

Ingestion of significant quantities of TTO has been described in a 17-month-old male who ingested less than 10 ml of the pure oil (100%) and developed ataxia and drowsiness (Halcón & Milkus 2004).

Accidental poisonings following TTO ingestion demonstrate that at relatively high doses, TTO causes Central Nervous System depression and muscle weakness (Jacobs & Hornfeldt 1994, Del Beccaro 1995, Morris et al. 2003, Elliott 1993, Villar et al. 1994, Seawright 1993). However, these symptoms had generally resolved within 36 hours.

The 29th Annual Report of the American Association of Poison Control Centers National Poison Data System (NPDS) analyzed the data obtained in the year 2011 from 57-seven participating centres (PC) serving the entire population of the 50 states, American Samoa, the District of Columbia, Federated States of Micronesia, Guam, Puerto Rico, and the US Virgin Islands. Among 1,376 TTO exposure cases, no or minor outcome was reported in most cases, minor outcome in 192 cases, major in 5 cases and no death. In 30 cases exposures were intentional with adverse reactions in 37 cases (Bronstein et al. 2012)

5.4. Laboratory findings

No data available.

5.5. Safety in special populations and situations

In vitro pharmacological interactions between TTO and conventional antimicrobials

(ciprofloxacin⁄amphotericin B) when used in combination were investigated. Interactions of TTO when combined with ciprofloxacin against Staphylococcus aureus indicate mainly antagonistic profiles. The interactions of TTO with amphotericin B indicate mainly antagonistic profiles when tested against Candida albicans. The authors concluded that the predominant antagonistic interactions noted, suggest that therapies with TTO should be used with caution when combined with antibiotics (van Vuuren et al. 2009).

Safety related to the use in pregnancy and lactation is unknown and therefore the use is not to be recommended.

5.5.1. Use in children and adolescents

The use in children under 12 years of age has not been established due to lack of adequate data.

5.5.2. Contraindications

Hypersensitivity to the active substance or to colophony as TTO cross-reacts with colophony (Norwegian Food Safety Authority 2012).

5.5.3. Special Warnings and precautions for use

Not to be used orally or as inhalation. Not to be used in eyes or in ears.

Not to be swallowed in case of use as a gargle or mouth wash.

If a rash develops discontinue use.

If fever or signs of exacerbating skin infection are observed, a doctor or a qualified health care practitioner should be consulted.

In cases of severe acne or for the eradication of fungal infection a doctor or a qualified healthcare practitioner shall be consulted.

If symptoms worsen during the use of the medicinal product, a doctor or a qualified health care practitioner should be consulted.

5.5.4. Drug interactions and other forms of interaction

None reported

5.5.5. Fertility, pregnancy and lactation

No fertility data available.

Safety during pregnancy and lactation has not been established. In the absence of sufficient data, the use during pregnancy and lactation is not recommended.

5.5.6. Overdose

None reported for the cutaneous use.

Accidental ingestion may cause central nervous system depression and muscle weakness. However, in adults these symptoms generally resolve within 36 hours (See “Acute intoxications” in section 5.3)

If ingestion occurs, the patient should be monitored and standard supportive treatment applied as required.

In children, ingestion of tea tree oil is a medical emergency requiring immediate hospital treatment and respiratory support.

5.5.7. Effects on ability to drive or operate machinery or impairment of mental ability

No studies on the effect on the ability to drive and use machines have been performed.

5.5.8. Safety in other special situations

Previous exposure to TTO or to several other essential oils with common chemical constituents known to be sensitizers may increase the possibility of allergic contact dermatitis reactions (Crawford et al. 2004).

Whereas fresh TTO seems to possess only a weak sensitizing potential, oxidized constituents of TTO increase their ability to act as allergens and as irritating agents (Harkenthal et al. 2000, Carson & Riley 2001, Norwegian Food Safety Authority 2012, Australian Government – Rural Industries Research and Development Corporation 2007). See also section Allergic reactions in 5.3 Adverse events and serious adverse events and deaths.

5.6. Overall conclusions on clinical safety

Clinical studies and traditional use show that short-term use (not more than 1 month) of diluted TTO on skin or mucosa is safe, but it is not suitable to be used in the eye or ear.

Reported adverse events were minor and mostly limited to local irritation. A case of blistering dermatitis has been reported with a wart paint containing TTO used for a period of 4 months.

There is some evidence that 100% TTO can cause allergic reactions in some patients. The rate of allergic reactions reported in the literature in various patch testing studies ranges between 0.6% and 2.4% (mean 1.6%). The incidence and strength of the reactions is generally higher with oxidised TTO samples. Proper storage and handling of TTO and its formulated products are needed to avoid the development of these by-products and reduce the risk of skin irritation and sensitisation in sensitive individuals.

Oral use results in poisoning. Accidental ingestion of 10-25 ml, demonstrates that at these relatively high doses, TTO causes Central Nervous System depression and muscle weakness. However, these symptoms had generally resolved within 36 hours.

TTO was not genotoxic in in vivo mouse micronucleus test (up to 1750 mg/kg). Ames test data are incomplete.

Tests on reproductive toxicity and on carcinogenicity have not been performed.

6. Overall conclusions

Despite several studies show that the antiseptic properties of TTO in various conditions no herbal medicinal product used in clinical trials with positive outcome is currently authorised in Europe for a least 10 years and therefore the “well-established medicinal use” cannot be supported. However results of clinical studies reinforce the plausibility of the traditional uses of TTO preparations.

TTO has been used as a traditional medicine for more than 30 years in Europe and worldwide, particularly in Australia for a number of indications. Some of them are supported by pharmacological or clinical data which confirm the antibacterial activity, antifungal activity, antiviral activity and antiprotozoal activity under controlled conditions. TTO has a broad spectrum antimicrobial activity with little evidence for inducing tolerance and resistance. TTO products are a useful addition to the range of

skin hygiene and protection products. This type of product has a known safety profile with a long history of traditional medicinal use.

Overall, a monograph on Melaleuca alternifolia (Maiden and Betch) Cheel, Melaleuca linariifolia Smith, Melaleuca dissitiflora F. Mueller and/or other species of Melaleuca, aetheroleum radix is established with the following preparations and therapeutic indications.

1)Traditional herbal medicinal product for treatment of small superficial wounds and insect bites: liquid preparation containing 0.5% to 10% of essential oil to be applied to the affected area 1-3 times daily; 1-2 drops (0.033-0.066 ml) of undiluted essential oil to be applied to the affected area using a cotton bud 1-3 times daily.

2)Traditional herbal medicinal product for treatment of small boils (furuncles and mild acne): oily liquid or semi-solid preparations containing 10% of essential oil, to be applied to the affected area 1-3 times daily or 0,7-1 ml of essential oil stirred in 100 ml of lukewarm water to be applied as an impregnated dressing to the affected areas of the skin or undiluted essential oil to be applied to the boil using a cotton bud 2-3 times daily.

3)Traditional herbal medicinal product for the relief of itching and irritation in cases of mild athlete´s foot: oily liquid or semi-solid preparations containing 10% of essential oil, to be applied to the affected area 1-3 times daily; 0.17-0.33 ml of essential oil in a bowl containing an appropriate volume of warm water to cover feet. Soak feet for 5-10 minutes a day; undiluted essential oil to be applied to the affected area using a cotton bud 2-3 times daily until the condition is cleared up.

4)Traditional herbal medicinal product for symptomatic treatment of minor inflammation of oral mucosa: 0.17 – 0.33 ml of TTO to be mixed in 100 ml of water for rinse or gargle several times daily for symptomatic treatment of minor inflammation of oral mucosa.

Adverse skin reactions including smarting pain, mild pruritus, burning sensation, irritation, itching, stinging, erythema, oedema, allergic reactions and allergic contact dermatitis have been reported. The frequency is not known. Sensitization is more likely to appear with oxidized TTO and therefore human adverse reactions may be minimized by reducing exposure to aged, oxidized oil. Proper storage and handling are needed to avoid the formation of oxidation products which have greater potential for skin sensitisation. Thus TTO should be in air-tight containers, protected from light and heat and a shelf-life after opening should be stated in the label of formulated TTO products on the basis of appropriate studies. Burn-like skin reaction has been reported. The frequency is rare (<1/1.000).

There is insufficient data to support the safety of TTO during pregnancy and lactation or in children under 12 years and therefore the use in this population groups is not recommended as a precautionary measure.

The data on safety are considered sufficient to establish a list entry for the above mentioned preparations and indications.