Eucalyptus oil is the generic name for the oil distilled from the leaf of Eucalyptus, a genus of the Myrtaceae plant family native to Australia and cultivated worldwide. Eucalyptus oil has a history of wide application, as a medicinal, antiseptic, repellent, aromatic and industrial use. The leaves of selected eucalyptus species are steam distilled to extract the eucalyptus oil.

Types and production
Eucalyptus oils in commerce are categorized into three general types according to their composition and primary end use: medicinal, aromatic and industrial. The most common is the typical cineol-based "eucalyptus oil", a colorless mobile liquid with a penetrating, camphorous, woody-sweet aroma.

Global production is dominated by Eucalyptus globulus. However, Eucalyptus kochii and Eucalyptus polybractea have the highest cineole content, ranging from 80 to 95%. The British Pharmacopoeia states that the oil must have a minimum cineole content of 70% if it is of pharmaceutical grade. Correction is used to bring lower quality oils to the required high cineol standard. The Eucalyptus genus also produces non-cineole oils, including piperitone, phallandrene, citral, methyl cinnamate, and geranyl acetate.

Uses

Herbal medicine:
The Committee for Herbal Medicinal Products of the European Medicines Agency concluded that traditional medicines based on eucalyptus oil can be used to treat the cough associated with the common cold and to relieve the symptoms of localized muscle pain.

Repellent and biopesticide:
Cineol-based eucalyptus oil is used as an insect repellent and biopesticide.

Aroma and taste:
Eucalyptus oil is also used in cooking. Cineol-based eucalyptus oil is used as a flavoring agent at low levels (0.002%) in a variety of products, including baked goods, confectionery, meat products, and beverages. Eucalyptus oil has antimicrobial activity against a wide range of foodborne human pathogens and food spoilage microorganisms. Eucalyptus oil is also used as a fragrance ingredient to impart a fresh and clean scent to soaps, detergents, lotions and perfumes. It is known for its spicy, intoxicating aroma. Due to its cleansing properties, eucalyptus oil is found in mouthwashes to freshen breath.

Industrial:
Research shows that cineol-based eucalyptus oil (5% of the blend) prevents the separation problem with ethanol and gasoline fuel blends. Eucalyptus oil also has a respectable octane rating and can be used as a fuel in its own right. However, production costs are currently too high for oil to be economically viable as a fuel.

Eucalyptus oils based on phallandrene and piperitone have been used in mining for the separation of sulphide minerals by flotation.

Cleaning:
Eucalyptus oil has natural antimicrobial and antiseptic properties and is used in household cleaning applications. It is commonly used in commercial laundry products and as a solvent to remove grease and sticky residue.

Safety and toxicity:
If taken internally at a low dose as a flavoring ingredient or in pharmaceutical products at the recommended ratio, cineol-based "eucalyptus oil" is safe for adults. However, systemic toxicity may result from ingestion or topical application at doses higher than recommended.
Eucalyptus oil has also been shown to be dangerous to domestic cats, causing unsteady gait, excessive salivation and other symptoms of ill health.