Tea tree oil
Tea tree oil, or melaleuca oil, is a pale yellow color to nearly colorless and clear essential oil with a fresh camphoraceous odor. 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.
History and extraction 
The indigenous Bundjalung people of eastern Australia use “tea trees” as a traditional medicine by inhaling the oils from the crushed leaves to treat coughs and colds. They also sprinkle leaves on wounds, after which a poultice is applied. In addition, tea tree leaves are soaked to make an infusion to treat sore throats or skin ailments.
Use of the oil itself, as opposed to the unextracted plant material, did not become common practice until researcher Arthur Penfold published the first reports of its antimicrobial activity in a series of papers in the 1920s and 1930s. In evaluating the antimicrobial activity of M. alternifolia, tea tree oil was rated as 11 times more active than phenol.
The commercial tea tree oil industry was born after the medicinal properties of the oil were first reported by Penfold in the 1920s. It was produced from natural bush stands of M. alternifolia that produced oil with the appropriate chemotype. The plant material was hand cut and often distilled on the spot in makeshift, mobile, wood-fired bush stills.
Production ebbed after World War II, as demand for the oil declined, presumably due to the development of effective antibiotics and the waning image of natural products. Interest in the oil was rekindled in the 1970s as part of the general renaissance of interest in natural products. Commercial plantations were established in the 1970s and 1980s, which led to mechanization and large-scale production of a consistent essential oil product.
Tea tree oil is defined by international standard ISO 4730 (2004) ("Oil of Melaleuca, Terpinen-4-ol type"), which specifies levels of 15 components which are needed to define the oil as "tea tree oil."
Medical use 
On humans 
Tea tree oil has been scientifically investigated only recently. Some sources suggest beneficial medical properties when applied topically, including antiviral, antibacterial, antifungal, and antiseptic qualities. The antiseptic properties can help in the fight against skin blemishes (acne). It also has beneficial cosmetic properties.
Tea tree oil is less successful for anti-microbial application in the nose. Also, there is clinical evidence that topical dermatological preparations containing tea tree oil may be more effective than conventional antibiotics in preventing transmission of CA-MRSA. It is also effective against canker sores, scientifically known as aphthous ulcers.
Recent studies support a role for the topical application of tea tree oil in skin care and for the treatment of various diseases and conditions. Tea tree oil appears to be effective against bacteria, viruses, fungal infections such as athlete's foot, mites such as scabies, and lice such as head lice. A 2008 study of in vitro toxicity showed a tea tree oil preparation was more effective against head lice than permethrin, a popular pharmaceutical remedy.
Tea tree oil is possibly effective against acne. In the treatment of moderate common acne, topical application of 5% tea tree oil has shown an effect comparable to 5% benzoyl peroxide. Albeit with slower onset of action, patients who use tea tree oil experience fewer side effects than those that use benzoyl peroxide treatments.
Tea tree oil is a known antifungal agent, effective in vitro against multiple dermatophytes found on the skin. Shampoo with 5% tea tree oil has been shown to be an effective treatment for dandruff due to its ability to treat Malassezia furfur, the most common cause of the condition.
One clinical study found that 100% tea tree oil administered topically, combined with debridement, was comparable to clotrimazole in effectiveness against onychomycosis, the most frequent cause of nail disease. It was not as effective at lower concentrations.
There is some very limited research that has shown that tea tree oil may have in vitro antiviral activity against the Tobacco Mosaic Virus, some strains of Herpes Simplex, and some bacteriophage viruses. 
In aquarium fish 
Diluted solutions of tea tree oil are often used as a remedy to treat bacterial and fungal infections in aquarium fish. Common brand names are Melafix and Bettafix. Melafix is a stronger concentration and Bettafix is a lower concentration that makes it harder to overdose smaller fish, especially bettas. It is most commonly used to promote fin and tissue regrowth, but is also effective in treating other conditions, such as fin rot or velvet. The remedy is used mostly on betta fish, but can also be used with other aquarium fish, other than goldfish.
Safety use 
According to the American Cancer Society: "Tea tree oil is toxic when swallowed. It 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."
Some people can 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 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.
One reported case of transient gynecomastia in a boy who was using a hair styling gel containing both lavender and tea tree oil suggests that tea tree oil may possess endocrine disrupting activity capable of leading to gynecomastia. Gynaecomastia resolved within a few months of stopping the product, and the Antiandrogen effects of lavender and tea tree oil were confirmed using human breast cancer cell lines.
If used in concentrations below 4% or particularly below 0.25%, tea tree oil may fail to kill bacteria and create selection pressure, which may result in them becoming less sensitive to tea tree oil and even some antibiotics in vitro.
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.
See also 
- Cajuput oil – derived from Melaleuca leucadendra
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