Classes of Compounds Found in Essential Oils

Essential oils are extracted from plants and used in the therapeutic practice of aromatherapy. The oils are made up of various chemical compounds. The main chemical compounds are terpenes, alcohols, phenols, ketones, aldehydes, lactones, oxides, acids and esters. Each chemical compound has different therapeutic properties and varies in reactivity levels.

Terpenes

• According to Patricia Davis in "Aromatherapy: An A-Z," terpenes are the most common type of compounds that are found in essential oils. Terpenes are sub-classified into monoterpenes, sesquiterpenes and diterpenes. According to Shirley Price in "Aromatherapy Workbook," monoterpenes are present in nearly every essential oil. The therapeutic properties of terpenes vary, depending on the sub-category. Price writes that terpenes are bactericidal, antiseptic and sometimes expectorant. Terpenes sometimes cause skin irritation in large quantities.

Alcohols

• According to Shirley and Len Price in "Aromatherapy for Health Professionals," alcohols are usually non-irritating to the skin. Alcohols are sub-divided into various categories, depending on the type of terpene compound that contributed to its formation. Categories include monoterpene, sesquiterpene and diterpene. According to Price and Price, alcohols are anti-infectious, bactericidal and anti-viral in their actions.

Phenols

• Phenols are more reactive than alcohols and are highly likely to cause skin irritation; essential oils that contain phenols therefore must be used with caution. Use in small quantities and do not use over a prolonged period of time. According to Price, phenols are bactericidal, antiseptic and stimulate the body's immune system.

Ketones

• Davis writes that ketones are the most toxic chemical compounds found in essential oils. Ketones have the potential to be abortive and cause damage to the nervous system. Ketones have valuable therapeutic properties if used in small quantities and for a short time. According to Price, ketones are calming, sedative, immunostimulant and capable of healing scars.

Aldehydes

• Price writes that aldehydes are more reactive than alcohols, but less reactive than ketones. According to Price, aldehydes are anti-inflammatory, anti-viral and calming to the nervous system. The strong aroma of aldehydes makes them a common ingredient in natural perfumes. Aldehydes cause skin irritation.

Lactones

• Lactones are found in essential oils that are expressed; these are predominately the citrus oils. The most common type of lactones found in citrus oils are coumarins and furocoumarins. Price writes that coumarins are sedative and calming. Furocoumarins cause sensitivity to sunlight. Use with caution before sunbathing.

Oxides, Acids and Esters

• Oxides are rarely found in essential oils. Eucalyptus oil, however, is one of the few oils that contain a high percentage of oxides. According to price, oxides are mucolytic and useful to treat coughs, colds and respiratory problems. They cause skin irritation. Acids are also rare in essential oils; they are found in a chemical reaction with an alcohol that forms an ester. Price writes that esters are anti-inflammatory and calming. They are usually non-reactive, except for the ester methyl salicylate, which is found in wintergreen oil and is not recommended for therapeutic aromatherapy practice.