Tea tree oil or melaleuca oil is a clear to very pale golden color essential oil with a fresh camphoraceous odor. It is taken from the leaves of the Melaleuca alternifolia which is native to the northeast coast of New South Wales, Australia. The oil has beneficial medical properties (including antiseptic and antifungal action), and is also believed to have beneficial cosmetic properties. Tea tree oil is usually used diluted, as reactions are common with pure tea tree oil.
Tea tree oil should not be confused with tea oil, the sweet seasoning and cooking oil from pressed seeds of the tea plant (drinking tea) Camellia sinensis 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.^[1][2]

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.^[3]

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 lead to mechanization and large-scale production of a consistent essential oil product.^[4]

Among over 98 compounds contained in the oil, terpinen-4-ol is responsible for most of the antimicrobial actions.^{citation needed}

Although tea tree oil is normally extracted from Melaleuca alternifolia commercially, it can also be extracted from Melaleuca dissitiflora and Melaleuca linariifolia. 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."

Composition

Compound	Tea tree oil ISO 4730 (2004) Concentration [%]
terpinen-4-ol	30-48
γ-terpinene	10–28
α-terpinene	5–13
1,8-Cineole	0–15
α-terpinolene	1.5–5
α-terpineol	1.5–8
α-pinene	1–6
p-cymene	0.5–8

Medicinal use

Tea tree oil has been recognized as a potent antiseptic in Australia anecdotally for much longer than there has been scientific evidence. However, recent studies support a role for tea tree oil in skin care and treatment of various ailments.^{[citation needed]}

Tea tree oil is a known antifungal agent, effective in vitro against multiple dermatophytes found on the skin.^[5] In vivo, 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.^[6]

Effectiveness of topical tea tree oil preparations for Candidiasis is supported by their ability to kill Candida in vitro.^[7]

In the treatment of moderate acne, topical application of 5% tea tree oil has shown an effect comparable to 5% benzoyl peroxide, albeit with slower onset of action.^[8] In another study in 2007 5% strength gel was compared against a placebo, with statistically significant results.^[9]

There is some limited research that has shown that tea tree oil may have topical anti-viral activity, especially with the Herpes virus (cold sores, chicken pox and shingles blisters, etc.)^[10]

One study has shown a 5% tea tree oil solution to be more effective than commercial medications against the scabies mite in an in vitro situation.^[11]