The medicinal parts of the plant are the leaves and branch tips from which the oil is extracted by steam distillation.
Flower and Fruit
The inflorescence is a 3- to 5-cm long spike. The flowers are sessile with a campanulate epicalyx on which the sepals sit. The tips are 3 to 4 mm long. The petals are free, approximately twice as large as the calyx tips. There are numerous conspicuous stamens, in 5 bundles approximately 2 cm long. The ovary is inferior and partially fused with the hollow receptacle. It is in 3 parts with a thick pistil and a capitular stigma. The fruit is a woody, cylindrical capsule with a diameter of 3 to 4 mm.
Leaves, Stem, and Root
This tree reaches heights up to 7 m. The leaves are simple, coriaceous, 1 to 2.5 cm long, acute-lanceolate, and sometimes slightly sickle-shaped with oil glands. The young shoots are tomentose, the older branches glabrous. The trunk has a paperlike, whitish bark.
Melaleuca alternifolia is indigenous to Australia.
Tea Tree oil is the essential oil extracted from the leaves and branch tips of Melaleuca alternifolia, Melaleuca dissitifolia, and other Melaleuca species by aqueous steam distillation. Ideally, the leaves and shoots have first been stored for 6 weeks.
Actions & Pharmacology
Terpinenes: Primarily terpinene-4-ol (45%), gamma-terpinene (18%), alpha-terpinene (8%), 1.8-cineole (6%), alpha-terpineol (5%), as well as alpha-pinene, limonene, p-cymol, terpinolene, viridiflorene
The in vitro data regarding the antimicrobial activity of Tea Tree oil is extensive, documenting it to be active against a wide range of bacteria, fungi, and yeast causing superficial skin infections. Tea Tree oil causes autolysis of bacteria during both the exponential and stationary phase of bacterial cell growth. Its effectiveness on the skin may also be attributed to its lipophilic nature causing it to penetrate the skin surface. However, few clinical studies have been done to confirm effectiveness and skin tolerance. The minimum bactericidal concentrations are typically close to 0.25% and many skin care products contain a concentration ranging from 1% to 10%.
As an antifungal, Tea Tree oil is rarely used as a monotherapy but instead combined with other antifungal natural products. Three comparative blinded trials showed Tea Tree oil to be effective in relieving the symptoms of athlete's foot, and in treating toenail onychomycosis.
Tea Tree oil is frequently recommended in either suppository or douche form as part of a treatment protocol for women with vaginal candidiasis or trichomoniasis; however, there is little documentation of the efficacy of this approach. Another use is as a “swish and spit” for patients with oral candidiasis. This is used in immunocompetent and immunocompromised patients.
Tea Tree oil is effective for treating acne vulgaris, with slightly less efficacy than benzoylperoxide. The oil had fewer side effects than benzoylperoxide. In a separate study, Tea Tree oil was found to be effective against head lice (Veal, 1996).
One study suggested that Tea Tree oil is similar in mechanism to the membrane-active disinfectants such as chlorhexidine and quaternary ammonium compounds by denaturing proteins and disrupting membrane structure. This is based on microscopic observation showing a loss of cell constituents and a breakdown of the cell wall after treatment of E coli cells with Tea Tree oil as well as the observation that cells were killed prior to autolysis. Tea Tree oil was also able to kill E coli cells in both the exponential phase and in the stationary phase of growth. Cells in the exponential phase of growth were killed after 30 minutes of Tea Tree oil treatment using the known minimum bactericidal concentration of 0.25% and in the stationary phase of growth in 45 minutes using twice the minimum bactericidal concentration (Gustafson et al, 1998).
Tea Tree oil inhibits cellular respiration and causes potassium leakage in E coli cells, further evidence that it is a membrane-active antibiotic. A concentration of 0.5% or 2x the minimum inhibitory concentration (MIC) caused exponentially growing cells to completely cease glucose-dependent oxygen consumption. In stationary phase cells, glucose-dependent oxygen consumption was decreased by 43% after increasing the concentration of Tea Tree oil to 1%, or 4x the MIC. This was accompanied by a leakage of potassium ions from the E coli cells that reached 75% using 0.25% Tea Tree oil on exponentially growing cells. Stationary phase cells are slightly resistant to Tea Tree oil, possibly due to alterations in the cell membrane that occur during this phase of growth (Cox et al, 1998).
Concentrations of Tea Tree oil greater than 300 mcg/mL had cytotoxic effects on fibroblasts and epithelial cells. Because this concentration also corresponded with the concentration that was cytotoxic to Staphylococcus aureus, the authors suggested that the mode of action for cytotoxicity is a membrane-associated event (Soderberg et al, 1996).
When eight components of Tea Tree oil were analyzed for antimicrobial activity, terpinen-4-ol inhibited all 12 of the test organisms, which were: Bacillus subtilis, Bacteriodes fragilis, Candida albicans, Clostridium perfringens, Enterococcus faecalis, Escherichia coli, Lactobacillus acidophilus, Moraxella catarrhalis, Mycobacterium smegmatis, Pseudomonas aeruginosa, Serratia marcescens, and Staphylococcus aureus. Linalool and alpha-terpineol were the next most effective, killing 11 of the 12 organisms. p-cymene was the least effective. The minimum cidal concentrations for linalool, terpinen-4-ol, and alpha terpineol were all 0.25% or less. Although it was previously stated that the antimicrobial activity of Tea Tree oil was due to terpinen-4-ol, this shows that linalool and alpha-terpineol are also very active, although there concentrations in Tea Tree oil are low (Carson & Riley, 1995).
Tea Tree oil was found to be active against a wide range of skin flora. These organisms include: A baumannii, Corynebacterium spp, K pneumoniae, M luteus, M varians, Micrococcus spp, P aeurginosa, S marcescens, S aureus, S capitis, S epidermidis, S haemolyticus, S hominis, S saprophyticus, S warneri, and S xylosus. The MIC ranged from 0.06% to 5% while the minimum bactericidal concentrations ranged from 0.25% to 8%. Generally, the gram-negative organisms were more susceptible to Tea Tree oil. The authors suggest that Tea Tree oil may be useful in hygienic hand disinfection by removing transient skin flora while maintaining protective resident flora. The technique used here was the broth microdilution method (Hammer et al, 1996).
Several species of Streptococcus were found to be susceptible to Tea Tree oil. Streptococcus pyogenes, a causative agent in impetigo, with an MIC of 0.12% Tea Tree oil and a minimum bactericidal concentration of 0.25% (Carson et al, 1996). Tea Tree oil was found to be effective against a number of oral bacterium, both anaerobic and capnophilic. The MIC for all 15 bacterial species tested was less <0.6% Tea Tree oil (Shapiro et al, 1994).
Tea Tree oil was found to be active against Malassezia furfur, the fungal agent implicated for pityriasis versicolor, folliculitis, and intertrigo, as well as seborrheic dermatitis and dandruff. Using an agar dilution assay, 52 isolates of M furfur gave an average MIC of Tea Tree oil of 0.25% after 72 hours. Using a broth macrodilution assay, 16 isolates were found to have an MIC of 0.12% and a minimum fungicidal concentration of 1.0% Tea Tree oil after 24 hours (Hammer et al, 1997).
Tea Tree oil was active against a variety of dermatophytes and yeasts. Clinical samples were collected from patients suffering dermatophytic disease and included 26 fungal specimens including Trichophyton rubrum, Trichophyton mentagrophytes, and Microsporum canis; 31 strains from the Candida genus and one Trichosporon and 31 different Malassezia furfur strains. The MIC ranged from 0.11% (1,112 mcg/mL) to 0.44% (4,450 mcg/mL) of Tea Tree oil. When compared to the antibiotic miconazole, minimum inhibitory values were lower, ranging from 0.1 to 0.78 mcg/mL (Nenoff et al, 1996).
Tea Tree oil was able to completely inhibit the growth of Candida albicans on agar. Tea Tree oil was diluted 1:5 in 90% ethanol and then 1:8 in agar plates. A dilution of 1:16 was the MIC. It was noted that Tea Tree oil from different sources gave variable results (McFadden, 1996).
Various essential oils were tested at 1% in 40% ethanol. Lice were dipped into the solution for 10 seconds, blotted dry, and then incubated for 17 hours. At this time the lice were washed, rinsed, and incubated for another 4 hours at which time live, dead, and morbid lice were counted. Similar procedures were done for lice eggs. A mixture of 50% Tea Tree oil and 50% Cinnamon Leaf oil killed 100% of the lice and 96% of the eggs. The dilution of Tea Tree oil alone killed 93% of the lice and 83% of the eggs. Although the results seem impressive, it is questionable as to whether appropriate controls were run or whether the procedure is relevant to how a product might be used in a clinical condition (Veal, 1996).
The efficacy of a 5% topical tea tree oil gel in mild to moderate acne vulgaris was investigated in a randomized, double-blind, placebo controlled study. Sixty patients were randomly divided into two groups and treated with tea tree oil gel (n=30) or placebo (n=30) over a period of 45 days. There was a statistically significant difference between tea tree oil and placebo in the improvement of the Total Acne Lesions Count (TLC) and Acne Severity Index (ASI). In terms of TLC and ASI, tea tree oil was 3.55 times and 5.75 times more effective than placebo respectively. Side-effects were similar in both groups (Enshaieh et al, 2007).
A 5% solution of Tea Tree oil was effective in treating acne vulgaris in a study of 124 patients who were randomized to receive either Tea Tree oil or 5% benzoylperoxide lotion for 3 months. It was not mentioned how often the treatment was used. Both groups showed improvement in the number of inflamed lesions, the number of noninflamed lesions, and skin oiliness (Bassett et al, 1990).
According to more recent interviews with 62 patients recruited from Australian general practice and dermatology offices, the use of tea tree oil and other complementary and alternative therapies for acne, psoriasis, and atopic eczema is far more common than physicians expected (Magin et al, 2006).
Clearance of Skin
Two topical MRSA eradication regimes were compared: a standard treatment including mupirocin 2% nasal ointment, chlorhexidine gluconate 4% soap, silver sulfadiazine 1% cream versus a tea tree oil regimen, which included tea tree 10% cream, tea tree 5% body wash, both given for five days. Mupirocin was significantly more effective at clearing nasal carriage (78%) than tea tree cream (47%, p=0.0001), but tea tree treatment was more effective than chlorhexidine or silver sulfadiazine at clearing superficial skin sites and skin lesions (Dryden et al, 2004).
A double-blind, longitudinal study of 49 nonsmokers assessed the effect of a gel containing tea tree oil on plaque and chronic gingivitis. The volunteers were randomly assigned to 1 of 3 groups designated to apply (without supervision) 1 of 3 gel formulations: tea tree oil gel (2.5%); gel with chlorhexidine (CHX; 0.2%); or a placebo gel. Participants were instructed to apply the gel with a toothbrush twice daily to inflamed gums. Over the course of eight weeks, those using the tree tee oil gel experienced more of a reduction in gingival inflammation than did those in the other groups. However, there was no reduction in plaque level with tea tree oil, suggesting that its antibacterial effects in vitro do not translate to plaque inhibition in vivo. The authors hypothesize that anti-inflammatory properties of tea tree oil helped to reduce gingivitis. No adverse reactions to any of the gels were reported. (Soukoulis, 2004).
Toenail Fungus (Onychomycosis)
A 100% solution of Tea Tree oil was effective in treating onychomycosis. In this double-blind randomized trial, 117 patients with distal subungual onychomycosis, proved by culture, applied either 100% Tea Tree oil or 1% clotrimazole twice daily for 6 months. At the end of 6 months, 11% of the clotrimazole group had a negative culture and 18% of the Tea Tree oil group was negative. Nail appearance improved in 61% of clotrimazole patients and 60% of Tea Tree oil patients. A 3-month follow-up showed that a positive resolution was still present in 55% of the clotrimazole patients and 56% of the Tea Tree oil patients (Buck et al, 1994).
Skin Inflammation (Histamine-Induced)
Tea Tree oil significantly decreased histamine-induced skin inflammation in 21 subjects 20 minutes after histamine injection in an open trial. Twenty-seven subjects were injected intradermally with histamine diphosphate (5 mcg/50 mcL) on each forearm. Flare area and weal volume was calculated after measuring weal diameters and double skin thickness every 10 minutes for 1 hour. Twenty-one subjects had 25 mcL of 100% Tea Tree oil topically applied to one forearm at 20 minutes while 6 subjects had 25 mcL paraffin oil topically applied to a forearm. The percentage weal volume of Tea Tree oil-treated arms was statistically significantly lower than that of the control arms (p=0.0004, Mann-Whitney U-test) at 30 minutes and at 60 minutes (p=0.017) (Koh et al, 2002).
Indications & Usage
Tea Tree Oil is used for conditions of the respiratory tract and for skin conditions. It is also used as a disinfectant. Folk medicine internal uses have included tonsillitis, pharyngitis, colitis, and sinusitis. Externally, Tea Tree Oil is used for ulcers of the oral mucous membrane, gingivitis, root canal treatment, mycosis of the nail, skin infections, ulcers, burns, and insect bites.
Tea Tree oil should definitely not be applied to eczematous skin as it can cause irritation. It is contraindicated for hypersensitivity or known allergy to turpentine (DeGroot, 1996). Although Tea Tree oil has been used orally for infections, this usage is not recommended due to its toxicity; the essential oil should not be used internally other than in the form of an oral rinse that is not swallowed or as vaginal douche. (Lininger et al, 1998).
Precautions & Adverse Reactions
Allergic contact dermatitis is said to be a common side effect of Tea Tree oil seen by Australian dermatologists. If sufficient quantities are ingested, diarrhea, central nervous system toxicity, and coma may occur (Moss 1994).
Cytotoxicity experiments found that the most toxic component of Tea Tree oil is alpha-terpineol and the least toxic is 1,8-cineole. HeLa cells (epithelial) were least affected while Hep G2 (liver) cells were most affected. This may or may not represent toxicity to the corresponding organs. The findings also suggest that 1,8-cineole is incorrectly credited with toxicity (Hayes et al, 1997). Except for mild irritation, there is no toxicity from using even 50% solutions as a douche for most patients.
Central Nervous System Effects
In one case report, a patient swallowed approximately half a teacup of Tea Tree oil and was in a coma for 12 hours, followed by 36 hours in a semiconscious state. This was accompanied by hallucinations, abdominal pain, and diarrhea. No further information was given (Seawright, 1993). In a separate case, a 4-year-old boy became ataxic and unresponsive about 2 hours after erroneously being given approximately 2 teaspoons 100% pure Tea Tree oil with a glass of water. After intubation, he began to move all limbs, muscle tone was normal, and pupils were sluggishly reactive. He was admitted to the intensive care unit for further observation and within several hours was weaned from the ventilator. Forty-eight hours after admission, he was discharged after having a normal physical examination (Morris et al, 2003).
Although 1,8-cineole has been credited for skin irritation associated with Tea Tree oil, a study showed that 1,8-cineole was not an irritant in concentrations up to 28.1%. This study was conducted on 28 human subjects for 21 days. However, three subjects showed signs of allergic responses to Tea Tree oil, which were due to the sesquiterpene hydrocarbon fraction of the oil (Southwell, 1997).
A report treating acne with 5% Tea Tree oil reported skin dryness, pruritis, stinging, burning, and redness as side effects (Bassett et al, 1990). Allergic contact dermatitis occurred from inhaling Tea Tree oil vapors. The patient had inhaled Tea Tree oil for several minutes, several times a day for 2 days as a treatment for bronchitis. The patient was previously atopic, with hand eczema and a known allergy to turpentine. He was also found to be allergic to several other essential oils (DeGroot, 1996).
Three case reports indicate that the common use of products containing Tea Tree oil, Lavender oil, or the two combined may result in prepubertal gynecomastia. The authors hypothesize that endocrine-disrupting activity of the topically applied oils led to an imbalance in estrogen and androgen pathway signaling in the case reports they describe—a hypothesis reinforced by the resolution of the gynecomastia within months of ceasing product use. In vitro data indicate that Tea Tree oil possesses weak estrogenic and antiandrogenic properties, as does lavender oil (Henley et al, 2007).
No human interaction data available.
In several cases involving children, overdosage (10 mL for a child) led to coordination weakness and a state of confusion. A very high dosage (70 mL) led to coma.
Mode of Administration
Preparations of the oil are used internally and externally.
Store tightly sealed and protected from light.