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Eucalyptus oil is the generic name for distilled oil from the leaves of Eucalyptus, a genus of the plant family Myrtaceae, mostly native to Australia but cultivated worldwide. Eucalyptus oil has a history of wide application, as a pharmaceutical, antiseptic, insect repellent, flavouring and fragrance, as well as having industrial uses. The leaves of selected Eucalyptus species are steam distilled to extract eucalyptus oil.
China produces about 75% of the world output, but most of that is derived from the cineole fractions of camphor laurel rather than being true eucalyptus oil. Significant producers of true eucalyptus include South Africa, Portugal, Spain, Brazil, Australia, Chile, and Eswatini.
Global production is dominated by oil from Eucalyptus globulus. However, Eucalyptus kochii and Eucalyptus polybractea have the highest Eucalyptol content, ranging from 80 to 95%. The British Pharmacopoeia states that the oil must have a minimum cineole content of 70% if it is pharmaceutical grade. Rectified spirit is used to bring lower grade oils up to the high cineole standard required. In 1991, global annual production was estimated at 3,000 tonnes for the medicinal eucalyptus oil, with another 1,500 tonnes being for the main perfumery oil, produced from Eucalyptus citriodora. The eucalyptus genus also produces non-cineole oils, including piperitone, phellandrene, citral, methyl cinnamate and geranyl acetate.
Non-cineole Eucalyptus dives, Eucalyptus olida and lemon ironbark are used as flavouring. Eucalyptus oil is also used as a fragrance component to impart a fresh and clean aroma in , , lotions, and . It is known for its pungent, intoxicating scent. Due to its cleansing properties, eucalyptus oil is found in to freshen breath.
Phellandrene- and piperitone-based eucalyptus oils have been used in mining to separate sulfide minerals via flotation.
The probable lethal dose of pure eucalyptus oil for an adult is in the range of 0.05 mL to 0.5 mL/per kg of body weight. Because of their high body-surface-area-to-mass ratio, children are more vulnerable to poisons absorbed transdermally. Severe poisoning has occurred in children after ingestion of 4 mL to 5 mL of eucalyptus oil.
Eucalyptus oil has also been shown to be dangerous to domestic cats, causing an unstable gait, excessive drooling, and other symptoms of ill health.Snopes, Are essential oils dangerous to cats?, 7 Jan. 2018
The known primary toxin in eucalyptus oil is eucalyptol.
In 1788, Dennis Considen and John White, surgeons on the First Fleet, distilled eucalyptus oil from Eucalyptus piperita, growing on the shores of Port Jackson, to treat convicts and marines.Maiden, J.H., The Forest Flora of New South Wales, vol. 4, Government Printer, Sydney, 1922. Copy of letter received by Dr Anthony Hamiltion , from Dennis Considen, 18 November 1788, and sent onto Joseph Banks.Lassak, E.V., & McCarthy, T., Australian Medicinal Plants, Methuen Australia, 1983, p. 15, . White, J., Journal of a Voyage to New South Wales, 1790 Eucalyptus oil was subsequently extracted by early colonists, but was not commercially exploited for some time.
Baron Ferdinand von Mueller, government botanist for the Colony of Victoria, promoted the qualities of Eucalyptus as a disinfectant in "fever districts", and also encouraged Joseph Bosisto, a Melbourne pharmacist, to investigate the commercial potential of the oil.Grieve, M.,(author) & Leyel, C.F., (ed), A Modern Herbal, Jonathon Cape, 1931, p. 287. Bosisto started the commercial eucalyptus oil industry in 1852 near Dandenong, Victoria, Australia, when he set up a distillation plant and extracted the essential oil from the cineole chemotype of Eucalyptus radiata. This resulted in the cineole chemotype becoming the generic 'oil of eucalyptus', and "Bosisto's Eucalyptus Oil" still survives as a brand.
French chemist, F. S. Cloez, identified and ascribed the name eucalyptol — also known as cineole — to the dominant portion of E. globulus oil.Boland, D.J., Brophy, J.J., and A.P.N. House, Eucalyptus Leaf Oils, 1991, p. 6 By the 1870s oil from Eucalyptus globulus, Tasmanian blue gum, was being exported worldwide and eventually dominated world trade, while other higher quality species were also being distilled to a lesser extent. Surgeons were using eucalyptus oil as an antiseptic during surgery by the 1880s.Maiden, J.H., The Useful Native Plants of Australia, pp. 255, 1889
Eucalyptus oil became an important industry in the box-ironbark forests of Victoria during the post gold-rush era of the 1870s. The oil was often described as Australia's natural wonder and was exported to a growing international market, mostly for medicinal purposes. Eucalyptus oil was in particularly big demand during the global influenza pandemic of 1918-19. A distillation plant was established by the Forests Commission Victoria at Wellsford State Forest near Bendigo in 1926. The Principal of the Victorian School of Forestry, Edwin James Semmens, undertook much of the pioneering chemistry into the composition of eucalyptus oil. His steam extraction kilns are in the museum at the school.
The Australian eucalyptus oil industry peaked in the 1940s, the main area of production being the central goldfields region of Victoria, particularly Inglewood; then the global establishment of eucalyptus plantations for timber resulted in increased volumes of eucalyptus oil as a plantation by-product. By the 1950s the cost of producing eucalyptus oil in Australia had increased so much that it could not compete against cheaper Spanish and Portuguese oils (being of lower cost due to their proximity to the European market). Non-Australian sources now dominate commercial eucalyptus oil supply, although Australia continues to produce high grade oils, mainly from blue mallee ( E. polybractea) stands.
Non-cineole oil producing species:
The former lemon eucalyptus species Eucalyptus citriodora is now classified as Corymbia citriodora, which produces a citronellal-based oil.
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