Essential oils are aromatic substances present in the specialized cells or glands of certain plants used by them to protect themselves from predators and pests, but also to attract polinators. In other words, essential oils are part of the immune system of the plant.
It has been shown that the saps and resins produced by some trees deter wood boring beetles. When eaten, other plant species are nauseating and toxic to mammals due to the chemical compounds found within.
In some environments plants are exposed to harsh climatic conditions, it is thought the essential oils which collect on the leaves of some plants protect against water loss.
The antimicrobial use of essential oils has been well documented when studied by man. Plants that produce these essential oils are better equipped to protect themselves against funguses and other microbes.
Even if the plant is situated in a near perfect environment not subjected to any of these trials, it may have to compete with other plants. Most essential oils contain compounds that are toxic to other plants by inhibiting respiration and photosynthesis – these are thought to be used to prevent other plants germinating in close proximity.
With many essential oils, we extract these and use them for the same or similar applications they were initially used for by the plant from which they came. In recent years the numbers of studies using essential oils for therapeutic benefits has increased.