Tea Tree Oil
Scientific Name(s): Melaleuca alternifolia Cheel.
Common Name(s): Melaleuca oil, Tea tree oil
There are many plants known as tea trees, but the species M. alternifolia is the source of tea tree essential oil. Native to Australia coastal areas, the tea tree is an evergreen shrub that grows from 5 to 8 m in height. Its narrow, 4 cm, needle-like leaves release a distinctive aroma when crushed. The fruits grow in clusters, and its white flowers bloom in the summer. Ornamental Leptospermum species are distinct and are not the source of tea tree oil. Related species include Melaleuca quinquenervia (Cav.) S.T. Blake (Melaleuca viridiflora sol.), a New Caledonian evergreen tree that yields niaouli oil, Melaleuca leucaden L., and Melaleuca cajuputi Powell (synonym, Melaleuca minor Sm.), which is the source of oil of cajuput that contains similar chemical constituents.1, 2
The indigenous people of Australia have used tea tree oil from crushed leaves as a traditional remedy for coughs and colds, as well as to treat wounds and skin conditions. Tea tree oil was first used in surgery and dentistry in the mid-1920s. Its healing properties were also used during World War II for skin injuries in munitions factory workers. Tea tree oil's popularity has increased in recent years as interest in natural therapies evolves, and it can be found in soaps, shampoos, and lotions.2, 3
The essential oil is normally obtained by steam distillation of the leaves and terminal branchlets, resulting in a transparent, colorless to pale yellow oil with a characteristic odor. The main constituent in tea tree's essential oil and present in concentrations of 30% or more is terpinen-4-ol, with more than 100 other constituents identified. The International Standards Organization requires 15 of these chemicals to be present, and concentrations of terpinen-4-ol must be at least 30% and 1,8-cineole (controversially considered a skin irritant) must be less than 15%. However, essential oils from other related species (Melaleuca dissitiflora and Melaleuca linariifolia) can also meet these same standards and have been used as adulterants. Other constituents include terpene endoperoxide (ascaridole), terpinene, terpinolene, pinene, cymene, and limonene. The composition of the essential oil may change with storage conditions, because heat, light, air, and moisture can affect the oil.2, 3, 4
Uses and Pharmacology
In vitro studies have confirmed bactericidal and bacteriostatic (at lower concentrations) action of tea tree oil. A broad spectrum of bacterial pathogens are affected, including common skin Staphylococcus species, Enterococcus faecalis, and Pseudomonas aeruginosa, and most are susceptible to concentrations of 1% or less of tea tree essential oil; however, the minimum inhibitory concentration (MIC) of some pathogens is as high as 8%. The activity has been attributed mainly to terpineol content, but some studies suggest that cineole has a role.2, 5, 6, 7 The leaf extract of the related species M. quinquenervia is considered weakly active against Helicobacter pylori with a MIC of 100 mcg/mL.40
A limited number of dermatological studies have been conducted in animals, particularly for chronic itching and fleas in dogs, but toxicity associated with ingesting the oil via licking limits therapeutic applications.2, 3, 8, 9
Despite the large number of in vitro studies reported, few quality clinical trials have been conducted. Clinical studies have been conducted in acne, methicillin-resistant S. aureus, and gingivitis. Case reports exist for use in bacterial vaginitis.10
One small trial established 5% tea tree oil to be more effective than placebo over 45 days in treating mild to moderate acne vulgaris.11 A second trial demonstrated equivalence with benzoyl peroxide 5% over 3 months of treatment; however, it may have been insufficiently powered to detect a difference.12 A Cochrane review of complementary therapies for acne identified 1 randomized trial (n=60) of low quality that showed a statistically significant benefit of tea tree oil gel for reducing the numbers of skin lesions in acne vulgaris compared to placebo (P<0.00001). Tea tree gel was applied for 20 minutes/day for a duration of 45 days. Adverse effects were minimal and similar between groups.42
In studies evaluating tea tree oil in the decolonization of MRSA nasal application of ointment (4% to 10%) and body wash (5%), no difference was shown versus mupirocin 2% and chlorhexidine or triclosan.13, 14 In subgroup analysis of data from the larger trial, mupirocin nasal ointment performed better than 10% tea tree oil in nasal decolonization, while tea tree oil performed better than chlorhexidine in decolonizing the skin and skin lesions.14 The results of a multicenter, open-label, randomized clinical trial on the effect of 5% tea tree oil wash in preventing methicillin-resistant S. aureus colonization in patients in the intensive care unit (ICU) was undertaken by a group of investigators in Northern Ireland.15 In this study (n = 391 evaluable), 5% tea tree oil body wash or control was used at least daily for bed baths until ICU discharge, or detection of MRSA colonization. There was no significant difference between treatment groups for incidence of MRSA colonization, and no patient in either group developed MRSA bacteremia.35
The American Academy of Dermatology/American Academy of Dermatology Association guidelines of care for the management of acne vulgaris (2016) states that topical tea tree oil is effective for the treatment of acne (limited; moderate).41
A wide range of yeasts, dermatophytes, and other filamentous fungi were susceptible to varying concentrations of tea tree oil. Reported MICs range from 0.12% to 2%, but some species (eg, Aspergillus niger ) require higher concentrations of up to 8%. It has been suggested that different phases of fungal growth are affected differently by tea tree oil.2, 3, 10, 18, 19
Despite an abundance of commercial preparations promoted for antifungal use, clinical trials of sound methodology are limited. Trials have been conducted in conditions including nail infections (onchomycosis), athlete's foot (tinea pedis), ringworm (tinea versicolor), dandruff, oral candidiasis, and case reports of other fungal conditions.
Equivalence was found for 100% tea tree oil and clotrimazole 1% in treating onchomycosis over 6 months in one study.20 However, a study evaluating butenafine with tea tree oil versus tea tree oil alone in treating fungal toenail infections found no effect for tea tree oil alone (the placebo arm of the study) applied over 8 weeks.21
Tea tree oil (25% and 50%) was better than placebo in treating tinea pedis in one clinical trial.22 A second trial found 10% tea tree oil to be no better than placebo in attaining a negative culture, but equivalent to tolnaftate 1% as assessed by reduction of symptoms.23 The popularity of tea tree oil in treating tinea pedis is attributed to the reduction of scaling, itching, and burning symptoms.8
A 5% tea tree oil shampoo used for 4 weeks was shown to be effective in treating dandruff, 24 and in an open-label study with no control arm, tea tree oil resolved oral candidial lesions in some, but not all, patients who were positive for HIV.25
Anti-inflammatory action has been described for tea tree oil and may account for observed clinical response of reduced itching. In histamine studies and nickel-induced contact hypersensitivity tests, tea tree oil reduced flare and erythema at higher concentrations (20% to 100%).2, 8, 28, 29, 37
Early studies examined the antiviral action of tea tree oil on tobacco mosaic virus, while in vitro studies in human viruses have been limited mainly to the herpes simplex viruses.2, 3 At 2.5 mcg/mL, tea tree oil suppressed herpes simplex virus type 1 in an in vitro study examining various oils.26 A small pilot study found some benefit in using a 6% tea tree oil gel in the treatment of recurrent herpes labialis over placebo; however, statistical significance was not achieved.27
Proctoial topical gel, a proprietary product containing hyaluronic acid with tea tree oil and methylsulfonylmethane, was evaluated in adult patients (n = 36) with grade 1 to 3 hemorrhoids in a randomized, double-blind trial. Patients were instructed to apply the study gel twice daily for 14 days. The active treatment was significantly better than placebo for symptoms including pain, pain during defecation, bleeding, pruritus, and inflammation.36
Decolonization of methicillin-resistant Staphylococcus aureus
Methicillin-resistant Staphylococcus aureus colonization prevention
Tea tree oil 5% body wash was used at least daily in 1 study that found no significant reduction in the rate of MRSA colonization.35
Onchomycosis (fungal nail infections)
100% tea tree oil applied for 6 months.20
Tinea pedis (athlete's foot)
Pregnancy / Lactation
Information regarding safety and efficacy in pregnancy and lactation is lacking. Alpha-terpinene, present in tea tree oil, was embryotoxic in rats.9
None well documented.
Case reports describe the irritant effect of topical tea tree oil in contact dermatitis.3, 9, 33 However, the irritant effect of tea tree oil, often attributed to the cineole constituent, has been disputed because 1,8-cineole concentrations of up to 28% have not produced reactions.2, 9 A study of tea tree oil in contact dermatitis reduced the concentration of tea tree oil from 50% to 20% because of skin irritation with the higher concentration.37 A relatively low concentration (ie, 1%) of ascaridole, a terpene endoperoxide that can develop in tea tree oil, has been shown to be a potential sensitizer based on data from 2 case studies.39
Internal doses of 10 to 70 mL have resulted in ataxia and decreasing levels of consciousness. Activated charcoal and sorbitol have been used as an antidote in cases of poisoning in children. No ongoing neurological sequelae have been reported.9
Reports of cytotoxicity experienced with tea tree oil vary, and mutagenicity is likewise unclear but appears to be low based on experimental data.9, 26 Ototoxicity has been evaluated in guinea pigs, and strengths of 2% or less are considered safe for use.9
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