Essential oils are, in essence, man-made. So, where Essential oils come from actually? Plant material is exposed to mechanical and chemical extraction processes that alter the chemical composition of the volatile oils (essences). The end result is an essential oil (extracted by steam or water distillation) or an absolute (extracted by solvent extraction or enfleurage).
But why do some plants contain aromatic essences? What is the purpose of their volatile oils?
Understanding Essential Oils Plant Essences Come From
Essential oils are sometimes incorrectly referred to as “essences.” However, they are not “pure” plant essences because they have been extracted and chemically changed. A pure plant essence is the substance secreted by a plant before it has been harvested and extracted. Many aromatic plants have secretory structures on their surface area or within their tissues, which secret volatile oils.
The oil-producing structures vary from plant species. They may be glandular trichomes (modified hairs), epidermal cells that secrete oils through their cellular walls, or secretory cavities or ducts (large spaces between cells) in plant tissues.
The essences, or volatile oils, are manufactured within the plant as a reaction to sunlight. Specialised plant cells called chloroplasts absorb sunlight and convert it into light energy in the form of glucose – a process known as photosynthesis. Chloroplasts surround secretory structures in plants and when they release their stored “sunlight” energy this allows other chemical reactions to take place. Plant essences are produced as a result of these chemical reactions, forming from molecules of oxygen, hydrogen and carbon.
How Do Plants Use Their Essential Oils Essences?
Plant essences have been referred to as the “life blood” of plants because they serve so many vital purposes, such as aiding pollination and reproduction, defense against insects and other pests, and protection against rival plants.
Aromatic plants use their plant essences to attract insects such as bees, butterflies and moths. The relationship between plant and pollinator is so close that the chemicals in plant essences have been found to match those in the odour glands of insects. Plants have also evolved to increase the production of their volatiles oils, and therefore increase their odour, at times of the day when pollinating insects are most active.
Volatile oils also help to protect plants against attack from pests, fungi and microbial infection or attack. For example, wild thyme and marjoram are mostly avoided by goats munching across the Mediterranean. These aromatic plants have a high concentration of the chemical terpene in their volatile oils, which is toxic to certain animals and deters them from eating the plants.
The same chemical compounds also protect plants from fungi and microbes. Other chemical compounds are also commonly used to deter insects; for example, essences high in camphene and citronellal (e.g. the essential oil, citronella, is commonly burned as an insect repellent).
Plants even use volatile oils aggressively in competition against other plant species. For example, the volatile oils in one plant may be toxic to a plant of another species, and prevent the rival plant from growing in the same area and sharing nutrition from the same soil, water and light. This is plant chemical warfare, and is called allelopathy. The chemicals responsible for this aggressive behaviour are called monoterpenes. The monoterpenes of some plants can be so toxic to other plant species that they can even impair the ability of their leaves to respire and photosynthesise.
Thus, essential oils originate from sunlight being absorbed by plants and kick-starting a chemical chain reaction that creates aromatic essences. They are referred to as the “life blood” of plants, performing many important biological reactions such as pollination, insect deterrent, and competition against other plants.