Key Chemistry

There is estimated to be around 3000 unique types of essential oils, and unique essential oil molecules. The main chemical structure is made from chemical compounds which have hydrogen, carbon and oxygen as their building blocks.

They can be divided into two groups:

a) the hydrocarbons which are made nearly exclusively of terpenes (monoterpenes, sesquiterpenes and diterpenes); 

b) the oxygenated compounds, mainly esters, aldehydes, ketones, alcohols, phenols and oxides. Acids, lactones, sulphur and nitrogen compounds are sometimes also present.

Terpenes (hydrocarbons)

A large and diverse class of organic compounds, produced by a variety of plants, particularly conifers, though also by some insects.


Anti-fungal, anti-septic, astringent, hypotensive, calms inflammation, spasms and pain.

Essential Oils: Sandalwood, Myrrh, Cedarwood


Anti-septic, anti-viral, stimulant, expectorant. Skin tonic. Slightly analgesic. Found in nearly all essential oils.

Essential Oils: Grapefruit, Frankincense

Oxygenated compounds


Most widespread compound in essential oils. Esters heal skin tissues from wounds, rashes and scars, they calm nerves, inflammation and spasms. Fungicidal. Sedative effect.

Essential Oils: Orange, Neroli


Anti-viral, anti-septic, anti-fungal. Lower fever and blood pressure. Calm nerves, and inflammation. Generally has a sedative effect. Found in lemon oils.

Essential Oils: Lemon, Lemongrass


Anti-fungal, decongestant. Secretory stimulant. Break down fat and aids the flow of mucus. Emmenagoguic (). Analgesic, sedative and cooling.

Essential Oils: Rosemary, Hyssop

Lactones & Coumarins

Decongest and stimulate flow of blood, lymph, sweat and catarrh. Hypotensive, sedative, balancing, uplifting.

Calm pain and inflammation. Rarely found in essential oils.

Essential Oils: Cinnamon

Aromatic Aldehydes

Anti-viral, anti-bacterial, anti-fungal. Lower fever and blood pressure. Calm inflammation.


One of the most useful group of compounds. Anti-viral, anti-septic anti-fungal, anti-bacterial. Tonic, stimulant (immune system), decongestant, diuretic, uplifting quailty. Generally non-toxic.


Anti-viral, bactericidal, parasiticidal, strong stimulating effect, tonic, sedative, decongestant, diuretic, emmenagoguic, raise blood pressure, calms pain, spasms and inflammation.

Essential Oils: Wintergreen


Derived from alcohols, terpenes, or ketones which have been oxidised. Cineol, eucalyptol. Expectorant effect.

Essential Oils: Eucalyptus, Ravensara



Julia Lawless, Encyclopedia of Essential Oils (London: Harper Collins Publishers, 2003).



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