With such increasingly troublesome pathogens as methicillin-resistant Staphylococcus aureus (MRSA) and the seemingly omnipotent nail fungus (onychomycosis), medical researchers are always searching for inventive tools to fight infections. Sometimes the solutions come from a breakthrough new chemical, but often the solution is found in an age-old remedy. Tea tree oil is one such entity. Having been used in its native Australia for hundreds of years as an all-purpose antiseptic, tea tree oil has enjoyed a surge of popularity worldwide over the past decade.

Background

Australian Aborigines have long used tea tree oil for healing skin lacerations, burns, and other infections. Tea tree oil is an essential oil made by steaming and distilling the leaves of the Melaleuca alternifolia plant, which is native to the coastal area of New South Wales.

While several chemically distinct oils are distilled from other Melaleuca species, the term has been adopted by the Australian Therapeutic Goods Administration as the official name for tea tree oil.1 According to local information, these leaves were originally used to make an aromatic tea, which is how the current name evolved.2 Tea tree oil is very pale to clear golden in color with a fresh, camphoraceous odor. Though there have been more than 98 compounds identified in the oil, terpinen-4-ol is responsible for most of its antimicrobial activity3

Tea tree oil is governed by the International Organization for Standardization, which specifies levels of 14 components necessary to define it as genuine.3 The composition of tea tree oil may change considerably during storage. Because of its great instability, tea tree oil purchased in its true form should be stored in an airtight container and kept away from heat and light.4 The more typical steam-extracted oils yield approximately a 2% solution.5

Science

Tea tree oil currently is being touted as a topical antiseptic and antifungal. In vitro studies also show antimicrobial activity against MRSA.6 The precise mechanism of action of tea tree oil is not known, but since it is a lipophilic compound, it is readily absorbed across membranes.7

One well-done clinical trial compared in vitro efficacy of tea tree oil against MRSA with that of the current treatment standard (mupirocin). The results were notable in that tea tree oil not only was effective, but the mean bactericidal concentration (MBC) levels were consistent across all the MRSA strains tested, whereas the MBC for mupirocin varied widely. The issues surrounding low levels of developing resistance to mupirocin have already been acknowledged in the literature, so the lack of variation among strains with tea tree oil is significant.8

Several randomized, controlled trials demonstrated equal efficacy of tea tree oil and clotrimazole for nail-bed fungal infection (both preparations required an average of six months of daily application).2 Efficacy was determined by absence of both observed symptoms and negative fungal cultures.

Tea tree oil has been studied for numerous skin conditions, including acne vulgaris. In one small trial against the active control of benzoyl peroxide, it showed similar success but took longer to show positive results.2

Safety

Though all indications are that tea tree oil is at least moderately effective as a topical antibacterial, there are safety concerns. Europe’s Commission E (the equivalent of the U.S. FDA) has refused to add tea tree oil products to its formulary, citing “unproven safety.”7 Anecdotal evidence suggests, however, that topical use is safe and that adverse events are minor, self-limiting, and infrequent.1

Tea tree oil can cause both irritant and allergic reactions. Relatively frequent reports of contact-type dermatitis have been appeared in the literature; all cases cleared completely within a few days of discontinuation.4 Skin reactions are linked to, but not totally dependent on, the strength of the essential oil in the compound.5

The more serious safety issues come from ingestion. Even though manufacturers strongly discourage any internal usage, occasional ingestion (whether accidental or intentional) does occur. Serious central nervous system effects (up to and including coma) develop rapidly after consumption of as little as a few milliliters. However, of known cases, all patients recovered completely, usually within a few hours.5 No human deaths due to tea tree oil have been reported in the literature.1

Recently, headlines reported gynecomastia in young male patients using soap and/or other cosmetic products containing tea tree oil. Clinicians confirmed these findings but remain unsure of the mechanism of action responsible for this unusual consequence. After use of the products was stopped, the gynecomastia resolved. Studies are under way to determine if there is an estrogenic action with repeated use of tea tree oil.9

Usage by small children or during pregnancy or lactation is not recommended.

Cost

Essential tea tree oil is relatively inexpensive at an average cost of $7 per 2-oz container. Many cosmetic products contain tea tree oil and vary widely in cost.

Summary

While notable, the efficacy data are not compelling, and there is significant risk for dermatitis. Current recommendations are not to keep tea tree essential oil in homes with young children. Given current information, tea tree oil appears not to be an answer to that pesky nail fungus.

References

1. Carson CF, Hammer KA, Riley TV. Melaleuca alternifolia (Tea Tree) oil: a review of antimicrobial and other medicinal properties. Clin Microbiol Rev. 2006;19:50-62.

2. About.com. Alternative medicine.

3. Wikipedia. Tea tree oil.

4. Skidmore-Roth L. Mosby’s Handbook of Herbs & Natural Supplements. 3rd ed. St. Louis, Mo.: Elsevier Mosby; 2006:967.

5. Fetrow CW, Avila JR. Professional’s Handbook of Complementary & Alternative Medicines. 3rd ed. Springhouse, Pa.: Springhouse Corp; 2001:631.

6. Mayo Clinic. Tea tree oil.

7. Cosmetics Designs. European Commission calls for proof on tea tree oil safety.

8. Elsom GK, Hide D. Susceptibility of methicillin-resistant Staphylococcus aureus to tea tree oil and mupirocin. J Antimicrob Chemother. 1999;43:427-428.

9. Henley DV, Lipson N, Korach KS, Bloch CA. Prepubertal gynecomastia linked to lavender and tea tree oils. N Engl J Med. 2007;356:479-485.