Aromatherapy
Essential Oil Chemistry - Why Aroma Matters
By Tarah Michelle Cech
Jan 17, 2008

Chemistry. Already getting nervous? The chemistry chapters of essential oil texts are the most frequently skipped, even by natural health professionals. But it can be fun and useful...really! Knowing what essential oils are made of, and how this affects their aroma and therapeutic value can have a big impact on the efficacy of your aromatherapy practice. Understanding the basics can help you make better choices in essential oils, and better choices in their application. Plus, this can give you the foundation for further understanding of true 'medical aromatherapy', as practiced in much of the rest of the world. So here's a primer on the chemistry of essential oils, with some common examples and important tips to help you grow as a holistic medicine practitioner.

So what is it that makes an essential oil different than every other oil we're familiar with? They don't feel the same, they don't act the same, and they certainly don't smell the same. Essential oils and the so-called 'fixed' oils (you may also know them as carrier or base oils - like Sweet Almond, Apricot Kernel, Evening Primrose, etc) are distinctly different in their molecular structure. While both essential and fixed oils share common basic atomic elements of Carbon and Hydrogen, that's really where the similarity ends. Fixed oils are made of triglyceride structures - three long chains of carbon atoms, with hydrogens bonded at various places. The length of the chains and the position and number of hydrogens define the nature of the oil; if hydrogens are bonded to every available location, the oil is 'saturated', for example. One missing hydrogen is 'mono-unsaturated', more than one is 'poly-unsaturated'. The long chains and relative consistency of the molecular structures makes fixed oils 'oily', and does not allow them to evaporate quickly.

Volatile oils are another matter - volatile oils do easily evaporate, due in-part to their smaller, more complex structures. Essential oils are a sub-category of volatile oils, essential oils being specifically those volatile oils that have been distilled directly from plants (rather than laboratory made, or from another otherwise 'inorganic' source). Essential oils still have a core structure of linked carbon and hydrogen atoms, but they come in a great variety of shapes including short chains, rings and multiple-rings hooked together. Each of these core structures will have what is known as a 'functional group' attached - a sort of 'molecular sub-unit'. Despite their seeming complexity, though, essential oils are still very compatible with mammalian biology - their atomic structure allows them to penetrate into the deepest regions of our bodies, and even to the centers of our cells.

Most of the therapeutic activity of an essential oil can be attributed to the functional groups of the individual chemicals that make up the oil. There can be over a hundred identifiable molecules in one essential oil. Each of these molecules, as mentioned earlier, is a chain or ring (or multiple-ring) structure of carbon atoms linked together with hydrogen atoms bonded to them in various configurations. Every chain or ring has a functional group attached - a functional group is defined by Salvatore Battaglia in 'The Complete Guide to Aromatherapy' as: "a single atom or group of atoms that...has a profound influence upon the properties of the molecule as a whole. It is often referred to as the chemically active center of the molecule".

As you can see, essential oils are really very complex in their chemical nature. There are nearly infinite possibilities of functional group and ring or chain combinations. And ONE essential oil alone can be made up of HUNDREDS of these different molecular arrangements. Don't worry, though! While it sounds complex, one needn't know all the precise chemical details to use essential oils therapeutically. When selecting between varieties of an essential oil, It IS helpful to know that any particularly oil is often composed of one or more primary molecular forms, with many minor or 'trace' constituents, and that ALL these molecules contribute to the oil's aroma and therapeutic action.

Many factors in an essential oil's production affect the total number and relative amounts of individual chemicals found in the final product. These include where the plant was grown, soil and climate conditions, time of harvest, distillation equipment, plus the time, temperature and pressure of distillation. This can give you an idea as to why two varieties of the same oil can smell so different: The full, beautiful bouquet of a fine essential oil will contain a myriad of notes, telling you that all natural components are present and in balanced amounts. Poorly distilled oils may lose some of the secondary constituents during production, and adulterated or synthetic oils may not have some of the trace components at all, detectable by your nose as a flat or uninteresting aroma.

As an example, let's look at Lavender, the most commonly used of all essential oils. More than 50 individual molecules are present in a high-quality Lavender. As noted earlier, all of these chemicals work together to produce a therapeutic effect. For example, 'linalool' is antiviral and antibacterial; 'linalyl acetate' is also emotionally calming; other constituents including cineol, limonene, alpha-pinene and others are all noted for specific biologic and aromatic activity. It is the combined, balanced action of these chemicals that make lavender such a useful healing agent - no one chemical can be singled out and used to give the same profound results.

So how is this synergy reflected in Lavender's aroma? Each of these chemicals has a unique smell; some are sweet, some are camphorous, some citrusy and some herbaceous. It is all these chemicals together, a precise amount of each, that gives each lavender variety its distinct aroma. And your nose knows this! One can tell the difference between a well-made, complex lavender oil with many notes within the aroma, and one that is flat or plain, which may be chemically imbalanced or missing some trace constituents. One can easily tell the difference, for example, between common Lavendula officinalis, and the finer Lavendula angustifolia, which contains a higher proportion of sweet-smelling linalyl acetate and less sharp-smelling camphor. Further, lower quality lavender plants may occasionally be sprayed with linalool before harvest to enhance the production of linalyl acetate by the flowers. While the end-product may smell sweeter, the process actually creates an imbalance in the overall healing synergy of the primary and trace molecules. All these oils will be labeled 'Lavender' on the store shelf, yet the finer, natural lavender will have a more beautiful, balanced aromatic bouquet, and is considered the most holistically healing variety by the world's leading aromatherapy practitioners.

A balanced approach in aromatherapy, as in all of natural medicine, is best. The most effective practitioner will have a well-developed 'internal pendulum' combined with a solid education. Significant variations exist in the quality of essential oils; it is really cost effective to buy the higher grades of oil, as their synergy of expertly distilled chemicals will have the greater therapeutic action. Use your nose, knowledge and intuition to find a source you trust, that delivers consistently high-grade oils for a reasonable cost. Use these same faculties to skillfully select and apply the appropriate oil for each circumstance. Essential oils are complex by nature; at the same time, they have an exceptionally broad scope of therapeutic applications. Hopefully, this little bit of aromatherapy chemistry will enrich your ability to support your own health, and the health of those around you.