An essential oil is a highly volatile concentrated aromatic substance, extracted from flowers, fruit peels), grass, leaves, seeds, roots or heartwood of a plant, by Distillation, Expression and Solvent Extraction.

Distilled aromatic plant oils are considered pure essential oils and are extracted. See the figure below : 

Large vats are filled with plant material which is steamed at a high pressure. The steam and essential oil vapour are then cooled, condensed to Liquid and then collected.

Expression is another method of extraction. Most citrus oils are obtained by simply cold pressed (squeezed) Lemon, Lime, Orange, Grapefruit, Mandarin, Tangerine, Bergamot are the oils obtained in this way.

Flowers or delicate smelling plant material are solvents extracted. This is an expensive and time-consuming process, where solvents such as Benzene, Butane, Alcohol and waxes are used. Tonnes of flowers are macerated (infused) in the solvents till saturated with the fragrance (of the plant material). Then they are centrifuged to separate the oil and wax from the solvent. The product of this process is called a Concrete. This concrete is then mixed with alcohol to be distilled in the vacuum with low temperature to obtain Absolute, and have the name mentioned E.g. Rose absolute, Jasmine absolute, etc. Macerated or infused oils are also used in Aromatherapy and are considered as Carrier or Base oils. This method of using essential oils is an ancient and a very fruitful way. A vegetable base oil has plant material added and heated or left in the Sun for a few days, until the plant material turns brown and there is no freshness left. Then it is redone with fresh plant material till the essential constituents are absorbed by the vegetable oil and smell strong enough. Ashwagandha, Lotus, Calendula, Hibiscus, Carrot, St. John’s Worth, Lime blossom, Melissa, Mullein flower are to name a few.

When using them in a blend, we use 10% to 30% of infused oil with other carrier oil and are blended with essential oils or by themselves.

Essential oils are also made of synthetic aromatic chemicals to get the fragrance of a particular plant material. These are called reconstitute oils (R.C.O.) and are manufactured for the use of modern Perfumeries and Cosmetics. The reconstitute essential oils have no or little therapeutical values and should never be used by an Aromatherapist. Many synthetic essential oils are considered highly toxic and can do more damage to the skin than good. It is very important to buy essential oils from a reputed supplier where quality is assured.

Vegetable oils, Base oils are also known as Carrier oils or Fixed oils and are used for dilution in Aromatherapy. Base oils are obtained as cold pressed, crushing to express the oil. These oils have a rich colour and a characteristic aroma with high contents of Vitamins and Minerals. Fixed oils is a compound of Glycerol and Fatty acids. Unlike Essential oils, Vegetable oils are greasy and do not evaporate leaving behind an oily stain on cloth or paper. Refined Vegetable oils have a complicated process of extraction, which involves heat. The colour is bleached; natural colour and odour are removed causing destruction to the Vitamin and Enzyme contents in the oil. The use of only cold pressed Carrier oils in Aromatherapy is therefore recommended.

Base oils are of two types. Light oils which are easily absorbed by the skin and which contain a major proportion of a massage oil mix. Heavy oils which are difficult to be absorbed by the skin are blended with light Carrier oils to the tune of 10% to 30%, due to its thick texture or cost. Lastly, we also use Macerated or infused oils as Carrier oils as mentioned earlier. But the choice of the Base oil or blend of Base oils to be used is a matter of personal preference or therapeutical needs.