Tea Tree Oil as a Topical Antimicrobial Agent
Tea Tree Oil as a Topical Antimicrobial Agent
May 1998; Volume 1: 52-56
By David Schiedermayer, MD
Tea tree oil (tto) is a pleasant-smelling essential oil with both antibacterial and antifungal properties. The oil contains molecules that can diminish or eliminate most pathogenic flora. Despite the potent nature of the concentrated oil, diluted or properly applied TTO products are reasonably safe alternatives to some popular prescription products for tinea pedis, onychomycosis, and bacterial vaginosis.
History, Culture, and Tradition
TTO is extracted from the narrow, pine-needle like leaves of Melaleuca alternifolia, a hardy Australian tree. Aboriginal peoples used the leaves to make poultices. In 1770 Captain James T. Cook and Dr. Joseph Banks (a botanist) brought leaves back to England for study, and Cook noted that the leaves had a lemon-tea like taste, thus, the name "tea tree."1
Table 1
Most active monoterpene components of TTO
1-terpinene-4-ol gamma-terpinene
rho-cymene alpha-terpineol
linalool terpinolene
alpha-terpinene 1,8-cineole
The oil was widely used by Australian troops in World War I to treat burns, infections, and other wounds.
The tea tree can grow elsewhere in similar thermoclimes and microenvironments, but Australia carefully guards the cultivation of the tree and the export of the oil, including maintaining an "Australian standard" for TTO meant to guarantee quality and minimize toxicity.
Pharmacology
Essential oils are extracted by steam distillation from the plant leaves and include such common oils as peppermint, eugenol, and thymol. These oils are easily aerosolized, highly absorbable, poorly soluble, and often have anti-microbial properties.
Gas chromatography of TTO reveals almost 100 compounds, with 21 of these yet to be identified. Of the 15 compounds present in highest concentrations, 12 are monoterpenes and three are sesquiterpenes (aromadendrene, cadinene, and viridiflorene). In this sense, TTO is similar to the resins of pine and spruce trees, which contain about 20-30% volatile monoterpenes. Of the 12 monoterpenes, the eight most active against organisms such as Candida albicans, Escherichia coli, and Staphylococcus aureus are shown in Table 1.2
The Figure shows the molecular structure of terpinene-4-ol. The hydroxyl group is on the 4 position of the benzene ring of this monoterpene.
The antimicrobial activity of TTO against Candida albicans correlates directly to the terpinene-4-ol level in the oil. No simple correlation exists between terpinene-4-ol levels and the anti-staphylococcal activity of TTO, which suggests that some other component of the oil is responsible for anti-staphylococcal activity. For Staphylococcus as well as Pseudomonas aeroginosa, the activity of pure rho-cymene was found to be higher than that for standard TTO and terpinene-4-ol. This suggests that, although rho-cymene is usually present at a concentration of 2-5% in TTO, its powerful antimicrobial activity makes an important contribution to the oil's overall activity.3
The "Australian standard" is that commercial Australian TTO must have a terpinene-4-ol content exceeding 30% and a 1,8-cineole content less than 15% (see below for a description of these compounds). This standard is maintained because terpinene-4-ol is considered to be the active antimicrobial constituent and 1,8 cineole is a potential skin irritant. TTO must be kept tightly capped and some experts believe it must be stored in amber bottles.
Mechanism of Action
The hydroxide group on the aromatic C-ring is important for cytoxicity. The antibacterial activity parallels cytotoxic activity, which suggests a similar mode of action.4 Cytotoxicity may contribute to decreased healing and increased scarring, both undesirable in burn treatment.
A study of cytotoxic effects of tea tree oil on human fibroblast cells incubated for one, four, 24, and 48 hours showed that concentrations up to 30 mcg/mL were nontoxic, but higher concentrations with more than four hours' exposure cause a rapid increase in cell death. The mechanism of cell death is likely due to the lipophilic character of the oil, which interacts with cellular membranes and disrupts normal membrane activity.4 This mechanism of action would also result in fungal cell or bacterial cell death.
Clinical Studies
Many of the claims made by manufacturers about these products date to the 1920s and 1930s, when limited knowledge existed about both TTO chemistry and microbiological growth inhibition techniques.5
A number of good studies performed in the last 10 years, however, indicate that TTO, if properly used, may have a role in the treatment of certain skin conditions.
In a single-blind, randomized, controlled trial of 124 patients comparing 5% TTO vs. 5% benzoyl peroxide for the treatment of mild to moderate acne, both were effective in ameliorating the patients' acne by reducing open and closed comedones. Although the action of TTO was slower, fewer side effects were experienced by patients treated by TTO.6
A double-blinded, multicenter, randomized, controlled trial of 117 patients at two primary care centers and a private podiatrist's office found that patients treated for onychomycosis with topical application of 100% TTO or 1% clotrimazole and assessed at one, three, and six months all had high recurrence rates. However, the two treatment groups were comparable based on culture cure ( TT 18%, CL 11%) and clinical resolution (TT 60%, CL 61%).7 Both of these therapies resulted in significant improvement in nail appearance and symptomatology.
A study of patients with tinea pedis treated with 10% TTO vs. placebo and tolnaftate showed significantly more tolnaftate-treated patients (85%) than TTO (30%) and placebo (21%) showed conversion to a negative fungal culture at the end of therapy. All three groups demonstrated a similar improvement in the clinical condition. TTO appears to reduce the symptomatology of tinea pedis as well as tolnaftate but is no more effective than placebo in effecting a mycobacteriological cure.8
A woman with symptoms of bacterial vaginosis and clue cells on exam declined conventional treatment with metronidazole and used a five-day course of TTO vaginal pessaries, each of which contained 200 mg of oil in a vegetable oil base. On follow-up exam, her vaginal secretions were normal and the clue cells were gone.9
The use of TTO in natural toothpaste has not been proven effective, and a major problem of natural toothpastes is that they lack fluoride, the only substance the FDA and the ADA recognize as effective in fighting dental decay.10
Formulation/Doses
The product is widely available in North American and Europe in an extensive range of cosmetic and medicinal products including antiseptic creams, hair care products, acne treatments, mouthwashes, and oil-impregnated toothpicks. (See Table 2 for cost comparison.)
In pharmacologic testing, all current preparations tested were sterile, which is an important consideration for any product that might be used on wounds. TTO may be useful in treating skin infections due to methicillin-resistant Staphylococcus aureus (MRSA) or muciprocin-resistant organisms. All 66 isolates of S. aureus tested in one study were susceptible to TTO, but 64 were MRSA and 33 were muciprocin-resistant.11
Andrew Weil, MD, gives a number of treatment regimens for TTO in his book, Natural Health, Natural Medicine.12 TTO can be painted on fungus-infected nails two to three times a day. Infected wounds should be cleansed and a 10% solution of the oil applied (about one and one-half teaspoons of the pure oil diluted in a cup of warm water). For a vaginal yeast infection, Weil suggests a douche with TTO diluted as described above. For acne, a 5% gel of TTO can be applied, or 1 mL of TTO can be diluted in 10 mL of water or equal quantities of rosewater and witch hazel. Other suggested dilutions include a 20.0% solution for cervicitis and 0.4% TTO in one quart of water as a daily douche to treat vaginal infections.
TTO should not be ingested orally, because it contains toxic hydrocarbons that can be absorbed through the stomach or aspirated into the lungs. The oil should not be used in full strength on injured skin or open wounds because of the toxicity to fibroblasts and the potential for systemic absorption.
Adverse Effects
Since the first description of contact allergy to TTO in 1991, 13 episodes have been reported. Common Melaleuca oil allergens have been found to be sd-limonene, aromadendrene, and alpha-terpinene. Most cases have been caused by the use of oil on diseased skin; occupational contact dermatitis has occurred in an aromatherapist and a beautician.13 Systemic contact dermatitis from ingestion of the oil has been observed.14
Clinicians are likely to see more contact eczema caused by increasing use of this popular nostrum.15 However, anecdotal reports note that constant handwashing with products containing tea tree oil does not lead to the dermatologic problems associated with some hand care preparations.18
TTO shows cytotoxicity against human fibroblasts and epithelial cells. Burnaid is a sorbalene-based cream containing 40 mg/g of TTO and 1 mg/g of triclosan. Testing was done against Enterococcus faecalis, S. aureus, E. coli, and Pseudomonas aeruginosa. Only S. aureus and E. coli showed zones of growth inhibition. No activity was found against E. faecalis or P. aeruginosa. The lack of activity of Burnaid against E. faecalis and P. aeruginosa, two microbes often found in burn wounds, along with the cytotoxicity to fibroblasts, must limit the potential use of the product for application to burns.17
A patient was comatose for 12 hours and semi-conscious for another 36 hours following ingestion of half a tea cup of neat tea tree oil.18 Tea tree oil toxicity has been reported in dogs and cats with the main symptoms of depression, weakness, uncoordination, and muscle tremors.19
Drug Interactions
Since TTO should only be used topically, no oral drug-drug interactions have been reported. However, the lipophilic nature of TTO and its ability to penetrate skin require further study of drug-drug interactions.
The unusual properties of the oil, including its ability to penetrate the outer layers of the skin, may enhance its antimicrobial activity against transient flora by means of a residual effect after handwashing.
Conclusion
TTO is an intriguing topical agent with a reasonably safe profile if used judiciously. Some early evidence of efficacy exists in the treatment of acne and fungal skin diseases, and for acne, this is probably a safe alternative to benzoyl peroxide. TTO should be diluted when used anywhere except on a fingernail or toenail. The oil should never be ingested.
May 1998; Volume 1: 52-56Subscribe Now for Access
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