Essential oils – the basics
The term “essential oil” is a contraction of the original “quintessential oil.” This stems from the Aristotelian idea that matter is composed of four elements, namely, fire, air, earth, and water.
The fifth element, or quintessence, was then considered to be spirit or life force.
Distillation and evaporation were thought to be processes of removing the spirit from the plant and this is also reflected in our language since the term “spirits” is used to describe distilled alcoholic beverages such as brandy, whiskey, and eau de vie.
The last of these again shows reference to the concept of removing the life force from the plant. Nowadays, of course, we know that, far from being spirit, essential oils are physical in nature and composed of complex mixtures of chemicals.
The International Organization for Standardization (ISO) in their Vocabulary of Natural Materials (ISO/D1S9235.2) defines an essential oil as a product made by distillation with either water or steam or by mechanical processing of citrus rinds or by dry distillation of natural materials.
Following the distillation, the essential oil is physically separated from the water phase.
For an essential oil to be a true essential oil, it must be isolated by physical means only.
The physical methods used are distillation (steam, steam/water and water) or expression (also known as cold pressing, a unique feature for citrus peel oils). There is one other method of oil isolation specific to a very limited number of essential oil plants. This is a maceration/distillation. In the process, the plant material is macerated in warm water to release the enzyme-bound essential oil. Examples of oils produced by maceration are onion, garlic, wintergreen, bitter almond, etc.
The Biological Role of Essential Oils Within Plants:
While essential oils are in the plant, they are constantly changing their chemical composition, helping the plant to adapt to the ever-changing internal and external environment. Recent scientific research has shown that plants produce essential oils for a variety of purposes including:
To attract pollinators and dispersal agents
Insects have been pollinating flowers for over 200 million years. Insects, like humans, are attracted to specific plants for one of three possible reasons: its aroma, its color, or its morphology or physical structure. Scent appears to be more ancient than flower color as an attractant to insects. Various insects, including bees, butterflies, and even beetles, are known to be attracted by the aroma of a plant.
To play a role in allelopathy, a type of plant-to-plant competition.
To serve as defense compounds against insects and other animals.
To protect the plant by their antifungal and antibacterial nature.
Plants store essential oils either in external secretory structures, which are found on the surface of the plant, or internal secretory structures, which are found inside the plant material.
Usually with plants having external secretory structure, you just have to lightly touch them and you will notice an aroma imparted to your skin. With plants having internal secretory structures, you may need to break the leaf or seed in order to get to the aroma/essential oil.
Be mindful and cautious if using on a client or patient – essential oils can cause allergic reactions. Additionally, veterans are triggered by certain scents (especially lavendar) may lead to PTSD symptoms. Always ask before use if using a new scent or with a new user!