Essential Oils

“In Chinese terms, essential oils are medicines for the Shen, the spiritual essence that resides in the heart and governs consciousness. In Ayurvedic terms, they enhance the flow of prana (life force), nourish ojas (nutritional/immunological essence), and brighten tejas (mental luminosity).” – David Crow

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.

According to Dr. Brian Lawrence (2000) “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.” (p. 8).

For our purposes, we shall summarize the above within the context of aromatherapy and therefore define essential oils as highly concentrated aromatic extracts that are distilled or expressed from a variety of aromatic plant material, including flowers, flowering tops, fruits/zests, grasses, leaves, needles and twigs, resins, roots, seeds, and woods. Robert Tisserand once wrote that ‘a pure essential oil is a vibrant dynamic which almost seems to have a life quality of its own’.

Essential oils display a set of general physical characteristics that give them their identity. In general, essential oils are:

Highly concentrated

This means that the therapeutic effect is considerably magnified. The fact that essential oils are highly concentrated makes them powerful agents, and often, due to their concentration, it is typically necessary to dilute them prior to use. Many aromatherapists believe that it is due to their incredibly high concentration that only a small amount is necessary to have therapeutic effects.

Volatile substances

Volatility refers to the ability of an essential oil to turn from liquid to vapor. An essential oil as a whole is volatile, and individual chemical constituents within an essential oil will volatize more or less quickly than others. For example, lemon is more volatile than vetiver, and limonene (a hydrocarbon terpene) is more volatile than borneol (an oxygenated hydrocarbon alcohol).

Light and nongreasy

The name essential oil can be deceptive. Essential oils are not vegetable or fatty oils, rather they are light, volatile substances that are referred to as “oils.” They have a consistency more like water (although they are insoluble in water) than oil and lack the oily texture of vegetable oils (with the exception of viscous essential oils, such as sandalwood, vetiver, and myrrh).

Mostly clear in color

Most oils have a slight hint of color from clear to light yellow. A few essential oils do have some color, for example, German chamomile, tansy, and yarrow are all a deep rich blue; patchouli can be dark brown; and bergamot can have a light green tint. Absolutes tend to be richer in color due to the chlorophyll and other plant pigments drawn out by the solvent. Resinoids, such as benzoin, myrrh, and frankincense, tend to be dark in color unless they are distilled.


Essential oils are lipophilic substances, which means they are attracted to and soluble in fatty substances. Essential oils have a strong affinity for lipids and are therefore soluble in:

  • Vegetable oils: Sweet almond, Sunflower, Apricot kernel, etc.
  • Herbal oils: Calendula, St. John’s wort, Comfrey, and Arnica
  • Full fat milk, cream, or honey
  • Essential oils are also soluble in alcohol and ether.


Viscosity is the measurement of an essential oil’s thickness. Viscous essential oils are less volatile than low-viscosity oils. Viscosity of an essential oil may slow down absorption through the skin. Viscous essential oils also tend to have a heavier aroma. For example, vetiver essential oil is very viscous compared to tangerine essential oil.

Highly complex chemically

Essential oils are made up of different combinations of a variety of chemical constituents. Some essential oils are considered to be simple in their chemistry, such as wintergreen or birch that contain up to 99 percent of one active constituent. Other essential oils are highly complex and contain over 100 different main constituents and hundreds more trace components. According to Schnaubelt (2004), “the therapeutic potential of essential oils arises from the synergistic action of the complex mixture of all its components” (p. 10).

Dynamic substance that exhibits a wide range of therapeutic activity

Essential oils exhibit a wide range of therapeutic activity, including psychological, physiological, spiritual, and energetic. One of the most researched aspects of essential oils is their antimicrobial and antiseptic activity. It is beyond doubt that essential oils are effective antifungal, antiviral, and antibacterial agents and that their natural aroma has an impact on our emotions, spirituality, perception, and behavior.

Essential Oils in Modern Times

Essential oils are produced for a variety of purposes, and they are distilled all over the world. They are utilized by a wide range of industries, including the cosmetic, pharmaceutical, tobacco, food and flavoring, and perfume industries. They are used as preservatives in cosmetics, flavors in food, insect repellants, fragrance compounds for perfumes and body care products, antimicrobial compounds in such products as mouthwashes, and masking agents for unpleasant odors. Essential oils and their isolated constituents have been the focus of research for their antimicrobial activity and other medicinal benefits. They offer a plethora of uses within the above industries as well as others.

This would lead one to wonder, are the essential oils used in all the above industries the same essential oils we use in aromatherapy? Most of the industries listed above are not necessarily concerned with the purity and wholeness of the essential oil, and in fact many will have fragrance oils made in a lab to maintain consistency in aroma or to reduce the cost of making a product. For genuine aromatherapy and effective applications, the purity and wholeness of the essential oil cannot be understated. We will be addressing this issue in the next chapter.

In the words of Schnaubelt (2004), “Genuine and authentic essential oils from plants are necessary conditions of wholistic aromatherapy. They are fundamentally different from the industrial, semi-natural oils which are commonly offered on the market. As semi-natural or synthetic oils are materially different from authentic oils it is logical that their physiological effects are also different. Most importantly, authentic oils are much less allergenic and irritant than their industrial counterparts.”

To learn more about the quality of essential oils, click here.

Top 12 Most Popular Essential Oils

  • Tea Tree Melaleuca alternifolia
  • Bergamot Citrus bergamia
  • Geranium, Rose Pelargonium x asperum
  • Lemongrass Cymbopogon citratus
  • Rosemary Rosmarinus officinalis
  • Lavender Lavandula angustifolia
  • Eucalyptus Eucalyptus globulus
  • Clary sage Salvia sclarea
  • Peppermint Mentha x piperita
  • Tangerine Citrus reticulata
  • Frankincense Boswellia carterii syn. thurifera
  • Fennel Foeniculum vulgare