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Tea tree oil (TTO), or melaleuca oil, is an essential oil with a fresh camphoraceous odor and a color that ranges from pale yellow to nearly colorless and clear. It is taken from the leaves of the Melaleuca alternifolia, which is native to Southeast Queensland and the Northeast coast of New South Wales, Australia. Tea tree oil should not be confused with tea oil, the sweet seasoning and cooking oil from pressed seeds of the tea plant Camellia sinensis (beverage tea) or the tea oil plant Camellia oleifera.
Tea tree oil is toxic when taken by mouth, but is widely used in low concentrations in cosmetics and skin washes. Tea tree oil has been claimed to be useful for treating a wide variety of medical conditions. It shows some promise as an antimicrobial. Tea tree oil may be effective in a variety of dermatologic conditions including dandruff, acne, lice, herpes, and other skin infections.
The name tea tree is used for several plants, mostly from Australia and New Zealand, from the family Myrtaceae, related to the myrtle. The use of the name probably originated from Captain Cook's description of one of these shrubs, that he used to make an infusion, to drink in place of tea.
The commercial tea tree oil industry originated in the 1920s when Arthur Penfold, an Australian, investigated the business potential of a number of native extracted oils; he reported that tea tree oil had promise as it exhibited powerful antiseptic properties.
Tea tree oil is extracted from Melaleuca alternifolia commercially.
Tea tree oil is defined by the International Standard ISO 4730 ("Oil of Melaleuca, Terpinen-4-ol type"), which specifies levels of 15 components which are needed to define the oil as "tea tree oil." The oil has been described as having a fresh, camphor-like smell.
Tea tree oil contains over 98 compounds, and has six chemotypes, which are oils with different chemical compositions. These include a terpinen-4-ol chemotype, a terpinolene chemotype, and four 1,8-cineole chemotypes. Terpinen-4-ol is the major TTO component responsible for antimicrobial and anti-inflammatory properties. A second component 1,8-cineole, is likely responsible for most allergies in TTO products. Adverse reactions to TTO diminish with minimization of 1,8-cineole content. In commercial production, TTO is prepared as a terpinen-4-ol chemotype.
In vitro studies show that tea tree oil is capable of killing MRSA in a laboratory setting. Studies have shown that it demonstrated similar rates of eradication when compared to treatment with mupirocin. A 2005 review stated that there is insufficient evidence to recommend routine use for this purpose in a clinical setting. A 2008 article from the American Cancer Society says that studies have found some promise of a possible role for the topical application of tea tree oil as an antiseptic, but that "despite years of use, available clinical evidence does not support the effectiveness of tea tree oil for treating skin problems and infections in humans". A 2012 review by the NIH rates Tea tree oil as "possibly effective" for three applications, saying that "a 5% tea tree oil gel appears to be as effective as 5% benzoyl peroxide" for treating mild to moderate acne, that "topical application of 100% tea tree oil solution, twice daily for six months, can cure fungal toenail infection in about 18% of people who try it," and that "a 10% tea tree oil cream works about as well as tolnaftate 1% cream" in treating symptoms of athlete's foot, although being less effective than clotrimazole or terbinafine.
A 2006 review of the toxicity of tea tree oil concludes that it may be used externally in its diluted form by the majority of individuals without adverse effect (provided oxidization is avoided). Tea Tree oil is poisonous when taken internally. Tea tree oil may be effective in a variety of dermatologic conditions including dandruff, acne, lice, herpes, and other skin infections. A 2012 review of head lice treatment recommended against the use of tea tree oil on children because it could cause skin irritation or allergic reactions, because of contraindications, and because of a lack of knowledge about the oil's safety and effectiveness.
Tea tree oil is a commercially refined composition of several naturally occurring chemical compounds and is hazardous if misused. Available literature suggests that TTO can be used topically in diluted form by the majority of individuals without adverse effects. Topical application of TTO can cause adverse reactions at high concentration. Adverse effects including skin irritation, allergic contact dermatitis, systemic contact dermatitis, linear immunoglobulin A disease, erythema multiforme like reactions, and systemic hypersensitivity reactions. The National Pediculosis Association in the United States states pure tea tree oil is contraindicated for use by pregnant women and children.
Tea tree oil is toxic when swallowed. According to the American Cancer Society, ingesting tea tree oil has been reported to cause drowsiness, confusion, hallucinations, coma, unsteadiness, weakness, vomiting, diarrhea, stomach upset, blood cell abnormalities, and severe rashes. It should be kept away from pets and children. Tea tree oil should not be used in or around the mouth. There is at least one case of poisoning reported in medical literature.
Exposure of tea tree oil to air and light results in oxidation of some of its components. Oxidized tea tree oil should not be used. Some people experience allergic contact dermatitis as a reaction to dermal contact with tea tree oil. Allergic reactions may be due to the various oxidation products that are formed by exposure of the oil to light and/or air.
In vitro testing of tea tree oil shows that it contains chemicals which are weakly estrogenic, causing particular concern for use with children. However in tests, the chemicals which show this effect failed to show absorption into the skin, and evidence of a hormonal effect is therefore considered implausible by an EU scientific committee.
In dogs and cats, death or transient signs of toxicity (lasting 2 to 3 days), such as depression, weakness, incoordination and muscle tremors, have been reported after external application at high doses. In rats the LD50 is 1.9-2.4 ml/kg.
Undiluted tea tree oil can cause some hearing loss when used in the ears of non-human animals; however, a 2% concentration has not been shown to have any lasting effect. It is not known whether the same is true for humans.