Tea tree oil, also known as melaleuca oil or ti tree oil, is an essential oil with a fresh camphoraceous odor and a colour that ranges from pale yellow to nearly colourless and clear. It is from the leaves of the tea tree, Melaleuca alternifolia, native to Southeast Queensland and the Northeast coast of New South Wales, Australia.
Tea tree oil is toxic when taken by mouth. Although there is little evidence of efficacy, it is typically used in low concentrations as a folk medicine for attempted treatments of skin conditions. Tea tree oil is claimed as useful for treating dandruff, acne, lice, herpes, insect bites, scabies, and skin fungal or bacterial infections. However, the quality of the evidence for efficacy in these conditions is minimal. Tea tree oil is neither a patented product nor an approved drug.
Tea tree oil has been used in traditional medicine in the belief it treats acne, nail fungus, or athlete's foot, with little evidence to support these uses. In a 2015 Cochrane systematic review, the only trial comparing it to placebo for acne found low-quality evidence of benefit.
Tea tree oil is not recommended for treating nail fungus, as the evidence for its effectiveness is weak, and does not suggest it would outperform conventional treatments. It is not recommended for treating head lice in children because its safety has not been established and it could cause skin irritation or allergic reactions.
Tea tree oil is poisonous when taken internally. It may 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. As a test of toxicity by oral intake, the median lethal dose (LD50) in rats is 1.9–2.4 ml/kg.
A 2006 review of the toxicity of tea tree oil concluded that it may be used externally in its diluted form by the majority of individuals without adverse effect (provided oxidation is avoided). Topical application of tea tree oil 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. Allergic reactions may be due to the various oxidation products that are formed by exposure of the oil to light and/or air. Consequently, oxidized tea tree oil should not be used.
Tea tree oil is defined by the International Standard ISO 4730 ("Oil of Melaleuca, terpinen-4-ol type"), containing terpinen-4-ol, γ-terpinene, and α-terpinene as about 70% to 90% of whole oil, while ρ-cymene, terpinolene, α-terpineol, and α-pinene collectively account for some 15% of the oil (table, right). The oil has been described as having a fresh, camphor-like smell.
Tea tree oil products may contain a range of chemical combinations containing over 98 compounds, with terpinen-4-ol as the major component. Adverse reactions diminish with lower 1,8-cineole content.
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 James 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 antiseptic properties.
Tea tree oil was first extracted from Melaleuca alternifolia in Australia, and this species remains the most important commercially. In the 1970s and 1980s, commercial plantations began to produce large quantities of tea tree oil from Melaleuca alternifolia. Many of these plantations are located in New South Wales. Since the 1970s and 80s, the industry has expanded to include several other species for their extracted oil: Melaleuca armillaris and Melaleuca styphelioides in Tunisia and Egypt; Melaleuca leucadendra in Egypt, Malaysia and Vietnam; Melaleuca acuminata in Tunisia; Melaleuca ericifolia in Egypt; and Melaleuca quinquenervia in the United States. Similar oils can also be produced by water distillation from Melaleuca linariifolia and Melaleuca dissitiflora. Whereas the availability and nonproprietary nature of tea tree oil would make it – if proved effective – particularly well-suited to a disease like scabies that affects poor people disproportionately, those same characteristics diminish corporate interest in its development and validation.
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.
A 2008 article from the American Cancer Society stated 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." Other uses under preliminary research include applications for nail fungus, dandruff, acne, scabies, and athlete's foot, but existing evidence is limited. 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,and lack of knowledge about safety and effectiveness.