Essential oils have been known and studied for nearly fifteen centuries. The uses of these natural products were originally aimed at medication and religious rituals in Egypt, India, China and Iran. Historically the first essential oil encountered perfumistically was rose oil: a Chinese emperor spread rose petals on a bathing pool and due to natural osmosis the water became pleasantly fragrant.
The first official reference to these materials appears in the late 13th Century; it is quoted that a certain Arnold de Villanova steam distilled rosemary and sage leaves, but no one really knows if he bothered to separate them from the water phase. It would, however, seem that as the end result the fragrance conveyed a pharmaceutical message: everyone in the village who de Villanova thought was ill was compelled to have a mouthful of his magic water. Once tasted, thereafter they were too afraid to get ill. So it did work.
An essential or volatile oil (these two terminologies are used synonymously) is a volatile mixture of organic compounds derived from one botanical source. These compounds are primarily responsible for the characteristic, distinctive and often diagnostic aroma of the basic product. Most essential oils exist in the source material, but certain oils are formed only as a result of a natural enzymatic reaction once the plant tissues have been crushed or macerated in an aqueous phase. These belatedly produced oils are then recovered by traditional methods.