Eucalyptus oil is the generic name for distilled oil from the leaves ofEucalyptus, agenus of the plant familyMyrtaceae, mostly native toAustralia but cultivated worldwide. Eucalyptus oil has a history of wide application, as apharmaceutical,antiseptic,repellent,flavouring andfragrance, as well as having industrial uses. The leaves of selectedEucalyptusspecies aresteam distilled toextract eucalyptus oil.
In the trade, eucalyptus oils are categorized into three broad types according to their composition and main end-use:medicinal,perfumery and industrial.[1] The most prevalent is the standardcineole-based "oil of eucalyptus", a colourless mobile liquid (which yellows with age), having a penetrating,camphoraceous,woody-sweet scent.[2]
China produces about 75% of the world output, but most of that is derived from the cineole fractions ofcamphor laurel rather than being true eucalyptus oil.[3] Significant producers of true eucalyptus includeSouth Africa,Portugal,Spain,Brazil,Australia,Chile, andEswatini.
Global production is dominated by oil fromEucalyptus globulus. However,Eucalyptus kochii andEucalyptus polybractea have the highestcineole content, ranging from 80 to 95%. TheBritish Pharmacopoeia states that the oil must have a minimum cineole content of 70% if it ispharmaceutical grade.Rectification 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 fromEucalyptus citriodora.[4] The eucalyptus genus also produces non-cineole oils, includingpiperitone,phellandrene,citral,methyl cinnamate andgeranyl acetate.
Eucalyptus oil is a common ingredient indecongestant formulations.[5] TheEuropean Medicines AgencyCommittee on Herbal Medicinal Products concluded thattraditional medicines based on eucalyptus oil can be used for treatingcough associated with thecommon cold, and to relieve symptoms of localized muscle pain.[6]
Cineole-based eucalyptus oil is used as aninsect repellent andbiopesticide.[7] In the U.S., eucalyptus oil was first registered in 1948 as an insecticide andmiticide.[8]
Cineole-based eucalyptus oil is used, at low levels (0.002%), as a flavouring in various products, includingbaked goods,confectionery,meat products andbeverages.[9] Eucalyptus oil hasantimicrobial activity against a broad range of food-borne humanpathogens andfood spoilagemicroorganisms.[10]
Non-cineolepeppermint gum,strawberry gum andlemon ironbark are used as flavouring. Eucalyptus oil is also used as afragrance component to impart a fresh and clean aroma insoaps,detergents, lotions, andperfumes. It is known for its pungent, intoxicating scent. Due to its cleansing properties, eucalyptus oil is found inmouthrinses to freshen breath.[citation needed]
Research shows that cineole-based eucalyptus oil (5% of mixture) prevents the separation problem withethanol andpetrolfuel blends. Eucalyptus oil also has a respectableoctane rating, and can be used as a fuel in its own right. However, production costs are currently too high for the oil to be economically viable as a fuel.[11]
Phellandrene- and piperitone-based eucalyptus oils have been used inmining to separatesulfide minerals viaflotation.
Eucalyptus oil is used in household cleaning applications.[12][13] It is commonly used in commercial laundry products such as wool wash liquid. It is used as a solvent for removing grease and sticky residue.[14]
If consumed internally at low dosage as a flavouring component or in pharmaceutical products at the recommended rate, cineole-based 'oil of eucalyptus' is safe for adults. However, systemic toxicity can result from ingestion or topical application at higher than recommended doses.[15] In Australia, eucalyptus oil is one of the manyessential oils that have been increasingly causing cases of poisoning, mostly of children. There were 2,049 reported cases inNew South Wales between 2014 and 2018, accounting for 46.4% of essential oil poisoning incidents.[16]
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.[17] 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.[18]
Eucalyptus oil has also been shown to be dangerous to domestic cats, causing an unstable gait, excessive drooling, and other symptoms of ill health.[19]
The known primary toxin in eucalyptus oil iseucalyptol.
Aboriginal Australians use eucalyptus leaf infusions (which contain eucalyptus oil) as a traditionalmedicine for treating body pains,sinus congestion,fever, andcolds.[20][21]
In 1788,Dennis Considen andJohn White, surgeons on theFirst Fleet, distilled eucalyptus oil fromEucalyptus piperita, growing on the shores ofPort Jackson, to treat convicts and marines.[22][23][24][25] Eucalyptus oil was subsequently extracted by early colonists, but was not commercially exploited for some time.
BaronFerdinand von Mueller, government botanist for theColony of Victoria, promoted the qualities of Eucalyptus as adisinfectant in "fever districts", and also encouragedJoseph Bosisto, aMelbournepharmacist, to investigate the commercial potential of the oil.[26] Bosisto started the commercial eucalyptus oil industry in 1852 nearDandenong,Victoria, Australia, when he set up a distillation plant and extracted theessential oil from the cineolechemotype ofEucalyptus 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 nameeucalyptol — also known ascineole — to the dominant portion ofE. globulus oil.[27] By the 1870s oil fromEucalyptus 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 anantiseptic duringsurgery by the 1880s.[28]
Eucalyptus oil became an important industry in thebox-ironbark forests of Victoria during the postgold-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 globalinfluenza pandemic of 1918-19. A distillation plant was established by theForests Commission Victoria at Wellsford State Forest[29] near Bendigo in 1926. The Principal of theVictorian School of Forestry,Edwin James Semmens, undertook much of the pioneering chemistry into the composition of eucalyptus oil.[30] 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, particularlyInglewood; then the global establishment of eucalyptus plantations fortimber 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.
Commercial cineole-based eucalyptus oils are produced from several species ofEucalyptus:
Non-cineole oil producing species:
The former lemon eucalyptus speciesEucalyptus citriodora is now classified asCorymbia citriodora, which produces acitronellal-based oil.
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