Essential oils can be subdivided into two distinct groups of chemical constituents; the hydrocarbons which are made up almost exclusively of terpenes (monoterpenes, sesquiterpenes, and diterpenes), and the oxygenated compounds which are primarily esters, aldehydes, ketones, alcohols, phenols, and oxides.
TERPENES - Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers. In others words, they are the building blocks of essential oils. There are two classes of terpenes: monoterpenes and sesquiterpenes. For a variety of industrial reasons, some perfumery companies “deterpenize” oils (lemon, for example where they remove the d-limonene) for the sake of creating a stronger scent. However, when you remove the terpenes, you also remove the main healing properties of these oils.
ESTERS - Esters are the result of a chemical reaction between organic acids and alcohols or phenols, and are the most widespread group found in essential oils. Most are generally mild and very stable compounds and their scents usually have a somewhat fruity tone to them, while others can be medicinal and potent. Esters are effective on inflammations and skin irritations, are anti-fungal, and have a relaxing and calming effect on the nervous system.
ALDEHYDES – aldehydes are most often found in lemony-smelling essential oils such as: citronella, lemongrass, and lemon eucalyptus but some oils have herbaceous and sometimes dry scents. Citrals are widely used in perfumery (synthetic aldehydes played an important role in the creation of Channel No 5). They are sometimes irritating to the skin and should be diluted before use, but they are highly effective when their scent is inhaled. Aldehydes have anti-infectious, anti-viral, anti-inflammatory and calming properties.
KETONES – when used responsibly, ketones can have powerful benefits including the ability to: calm, sedate, heal wounds, work as an expectorant, and be used as an anti-inflammatory. But, they can also be the most potentially dangerous when safety guidelines are ignored. The most toxic ketone is Thujone found in mugwort, sage, tansy, thuja and wormwood oils. Other toxic ketones found in essential oils are pulegone in pennyroyal, and pinocamphone in hyssop. It is said that ketones can cause epileptic seizures, induce abortion and wreak havoc on the central nervous system. Misuse usually occurs when proper daily dosages are ignored, resulting in a toxic buildup in the body. For example, let’s say that an oil has a daily recommended dosage of only four drops on the skin and every day you have been using six drops. The theory is that those extra two drops cannot escape your system and will build up over time – so, after ten days, you have an extra twenty drops roaming around your system. Oils that contain a smaller amount of ketones include: roman chamomile, lavandin, peppermint, and spearmint.
ALCOHOLS - are known for their antiseptic, anti-infectious, and anti-viral properties. They create an uplifting quality and are regarded as non-toxic. Most alcohols in essential oils have a sweet, green, or sometimes woodsy smell and are light and pleasant.
PHENOLS – are very similar to alcohols with the exception that they normally have a more biting and medicinal smell. Phenols are analgesic, antiseptic, anti-infectious, antispasmodic, antiviral, bactericidal, digestive, diuretic, expectorant, sedative, and immune system stimulants. However, oils high in Phenols are considered the most irritating oils for the skin and mucous membranes and can cause dermatitis and sensitization. If phenols are present in high concentrations in an essential oil, that oil should be used in very low dilutions on the skin and only used for short periods. A few examples of these oils are clove, thyme, and basil.
OXIDES - oxides are most often used for their antiseptic, decongestant and expectorant properties. Oxides usually have fresh, sharp, and medicinal aromas. Some examples include: eucalyptus, rosemary, cajeput, and tea tree.