An Essential Oil Chemistry Primer

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.

The therapeutic action of an essential oil is primarily determined by the functional groups found in the molecules that make up that oil (here, many folks might be responding with “Say what?!?”). An essential oil is actually made up of many liquid chemicals; sometimes more than one hundred distinct chemicals are found in one pure essential oil. Each of these chemicals is formed of a carbon-hydrogen structure with a functional group attached – it is the combination of the base structure AND the attached functional group that makes a single, unique molecule. And MANY of these unique molecules combine to form ONE essential oil.

The extremely complex nature of essential oils becomes apparent from this description. There are an almost infinite number of molecular combinations that can be formed from the building blocks of chains, rings and functional groups. And any SINGLE essential oil is made of many, sometimes even hundreds of these molecular combinations. Yet while this may sound complex, you needn’t know ALL the chemical details to use oils therapeutically. It IS helpful to know that each oil is made of many molecular forms, that all the molecules within each oil exert some biologic effect, and that it is the SYNERGY of ALL these molecules together that create the sum total of an oil’s therapeutic action AND its aroma. Nearly every laboratory study comparing complete, pure essential oils to one singled-out molecule that was thought the ‘active ingredient’ shows the essential oil to be more active.

The best natural, undiluted, properly distilled essential oils with all the major and minor chemical constituents will have the finest aromas AND the most potent 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.

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.

What does this mean to the lay-practitioner? That it’s important to find a nice smelling lavender oil! Each of the individual chemicals has a distinct smell, talked about in terms of ‘notes’ within the overall lavender aroma. Some of these are sweet, some citrusy, some are herbaceous, and some can be camphorous. A precise amount of each will create a certain lavender aroma. Some lavenders are more sweet (and therefore more relaxing), others are more herbaceous (and more anti-microbial). Three important points should be noted regarding selecting by aroma: First, there can be significantly different aromas from the same species of plant, even when the essential oils are of the highest quality. You can often use your intuition to select the best variety for your needs (as between the sweeter more relaxing, or the herbaceous more ‘medicinal’ lavenders). Second, some plants (e.g. Rosemary and Thyme) have chemotypes – this specifies a predominant chemical in the essential oil – each being used for a certain therapeutic application. Know which chemotype is best suited to your needs before making a selection. Finally, it is most often the essential oil that smells the most ‘true’ to you that will be the most beneficial. Your senses can naturally detect what is good for you and what is not, if you’re willing to listen to them impartially.

All essential oils are subject to similar variations in production methods or the manipulation of their molecular make-ups through the addition of synthetic chemicals. For the most therapeutic benefit, it is always best to use true, carefully-made essential oils. To do this, find a source that is dedicated to supplying only the highest grades of oils. Examine their product’s aromatic quality and business practices and so that you are comfortable with their dedication to your health, not just their bottom line. Listen to your intuition and your own nose; they won’t lie to you! With experience, your ability to discern between subtly different grades of oils will become more astute. With even more education and skill, you’ll start to recognize individual chemicals within an oils aroma, and make the best decisions as to which oils will have the most profound therapeutic affects for you, your family, or in your professional practice.