Tea-Tree Essential Oil
Do not confuse the tea tree with the unrelated common tea plant that is used to make black and green teas. The tea tree was named by eighteenth century sailors, who made tea that smelled like nutmeg from the leaves of the tree growing on the swampy southeast Australian coast.
The volatile essential oil derived mainly from the Australian native plant Melaleuca alternifolia. Employed largely for its antimicrobial properties, TTO is incorporated as the active ingredient in many topical formulations used to treat cutaneous infections. It is widely available over the counter in Australia, Europe, and North America and is marketed as a remedy for various ailments.
The seminal paper by Brophy and colleagues examined over 800 TTO samples by gas chromatography and gas chromatography-mass spectrometry and reported approximately 100 components and their ranges of concentrations.
TTO has a relative density of 0.885 to 0.906 , is only sparingly soluble in water, and is miscible with nonpolar solvents. TTO is produced by steam distillation of the leaves and terminal branches of M. alternifolia. Once condensed, the clear to pale yellow oil is separated from the aqueous distillate. The yield of oil is typically 1 to 2% of wet plant material weight.
Of all of the properties claimed for TTO, its antimicrobial activity has received the most attention. The earliest reported use of the M. alternifolia plant that presumably exploited this property was the traditional use by the Bundjalung Aborigines of northern New South Wales. Crushed leaves of “tea trees” were inhaled to treat coughs and colds or were sprinkled on wounds, after which a poultice was applied . In addition, tea tree leaves were soaked to make an infusion to treat sore throats or skin ailments . The oral history of Australian Aborigines also tells of healing lakes, which were lagoons into which M. alternifolia leaves had fallen and decayed over time . Use of the oil itself, as opposed to the unextracted plant material, did not become common practice until Penfold published the first reports of its antimicrobial activity in a series of papers in the 1920s and 1930s.
A broad range of bacteria have now been tested for their susceptibilities to TTO, While most bacteria are susceptible to TTO at concentrations of 1.0% or less, MICs in excess of 2% have been reported for organisms such as commensal skin staphylococci and micrococci, Enterococcus faecalis, and Pseudomonas aeruginosa . TTO is for the most part bactericidal in nature, although it may be bacteriostatic at lower concentrations.
The loss of intracellular material, inability to maintain homeostasis, and inhibition of respiration after treatment with TTO and/or components are consistent with a mechanism of action involving the loss of membrane integrity and function of the Bacteria.
References:
Carson CF, Hammer KA, Riley TV. Melaleuca alternifolia (Tea Tree) oil: a review of antimicrobial and other medicinal properties. Clin Microbiol Rev. 2006;19(1):50-62. doi:10.1128/CMR.19.1.50-62.2006
https://www.webmd.com/