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

Types and production
Eucalyptus oils are commercially categorized into three general types depending on their composition and primary end use: pharmaceutical, aromatic and industrial. The most widespread is the typical "eucalyptus oil" based on cineole, a colorless mobile liquid with a penetrating, camphoraceous, 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. Rectification is used to bring lower quality oils up to the required high cineole standard. The genus Eucalyptus also produces non-cineole oils, including piperitone, phallandrene, citral, methyl cinnamic acid, 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 coughs associated with the common cold and to relieve symptoms of localized muscle pain.

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

Aroma and taste:
Eucalyptus oil is also used in cooking. Cineole-based eucalyptus oil is used as a flavoring 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-spoiling microorganisms. Eucalyptus oil is also used as a flavoring 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 cineole-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 on its own. However, production costs are currently too high for the oil to be economically viable as a fuel.

Eucalyptus oils based on phallandrene and piperitone have been used in mining to separate sulfide minerals through 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:
When consumed internally at low doses as a flavoring ingredient or in pharmaceutical products at the recommended ratio, cineole-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.