Essential oils are the soul of plants. They are responsible for the fragrance of each plant.

When we smell a rose, peel an orange or ruffle a rosemary leaf between our fingers, it is the volatilizing essential oil that gives us this wonderful olfactive sensation.

However, the function of essential oils is not so much to please us as to serve the plant. Their smell attracts pollenizer insects, repels harmful bugs and protects the plant against a number of bacterial and cryptogamic diseases.

Also called essences, essential oils are created in the secretory cells of the aromatic plants from sugars produced by photosynthesis. These tiny drops of oil are then concentrated in pockets located in various parts of the plant: flowers, stalks, leaves, fruits, seeds, peels, roots, wood, bark, branches, needles, resin, moss, bulbs or rhizomes.

Essential oils require a lot of light and heat. It is for that reason that most aromatic plants grow in warm and sunny regions. Often, intense heat is enough to make these plants exhale their aroma.

The essential oils from certain plants are released through simple contact or friction of the parts that contain them. In contrast, the essential oils found in roots (ginger) or in wood (cedar) escape only if the oil cells are mechanically broken. In other words, one has to crush or grind plant material to express the oil. In citrus fruits, the aromatic substances are found in the peel which must be compressed to extract the aroma from the oil within.

Essential oils are highly odoriferous, volatile and flammable liquids that are also used outside aromatherapy. They are found in a wide range of everyday products such as pharmaceuticals, toothpaste, chewing gum, food flavourings, cosmetics and other household items.

Some plants yield several types of essential oil. This is true for the orange tree: neroli oil is extracted from its flowers, petit grain oil comes from its leaves and fruits, and orange tree oil is produced from its fruits. In some case, like peppermint, essential oil is extracted from the entire plant. 

There are many ways to typify essential oils. One consists of identifying them by their Latin name, which conveys the origin of every botanical species. We can also qualify them based on their method of extraction. Another way is to group them according to the type of sensation they produce when applied: warm effect with rubbing action, or cold effect with sedative and spasmolytic action. Finally, essential oils can be subdivided in olfactive families: floral, forested, spicy, hesperidium (citrus fruits), fruity, aldehyde and chypre.

Essential oils are quite different from the oil we use daily. They are non-fat oils. A drop of essential oil on a sheet of paper will leave no or very little oily residue after evaporation.

Carrier oils, on the other hand, are more similar to the oils we know well. They are called fixed oils. The most commonly-used carrier oils are olive, jojoba, sunflower, grape seed, Hypericum, aloe, sweet almond, pumpkin seed, hazelnut, sesame and macadamia nut oil.

The extraction method for any essential oil depends on the secretory organ of the plant.

Extracting the pure essential oils from plant and flower material is a lengthy and expensive process. A great deal of botanical material is required to make a small amount of essential oil. For instance, you need 200 kg of lavender to make 1 kg of essential oil, 1,000 kg of Neroli to make 1 kg of essential oil and 3,000 kg of rose petals to make 1 kg of rose oil. You need 120,000 rose petals to produce 15 ml of pure rose essential oil, and about 8 million hand picked jasmine blossoms to produce only 1 kilogram of pure jasmine essential oil.

Some plant materials, like sandalwood, must be properly aged before they can be used in the manufacturing of essential oils. The sandalwood tree must reach the age of 36 years and be thirty feet high before it can be cut down and distilled. This explains why some pure essential oils can be expensive.

Several companies claim to sell pure essential oils. Yet their oils are not pure as they are adulterated (mixed) with other vegetable oils to cut costs and increase profits. These products are commonly referred to as "branded" oils.

Others market synthetic oils as essential oils. Although their fragrance can be similar to the genuine natural oil, these synthetic copies have no therapeutic properties.