By | May 21, 2019

A critical take on the theory after almost 30 years of its existence, featuring 6 international experts in aromatherapy and essential oil research.

In aromatherapy, when it comes to essential oil chemistry, things may look surprisingly simple. You may have heard of phrases such as:

  • To prepare a wake-up blend, choose essential oils high in alcohols
  • Roman chamomile essential oil prevents spasms because it is rich in esters
  • You should avoid using essential oils rich in ketones because they are neurotoxic

Sounds elegant and yet sophisticated, right? These are just a few examples of claims that are based on the idea of functional groups, the only approach within aromatherapy with the status of some sort of a theory: an organised set of knowledge with predictive value.

Mastering classification of essential oil constituents into functional groups, the theory goes, we should be able to understand why certain essential oils have similar effects, and moreover to design blends precisely targeted for specific problems. Many aromatherapists have adopted such a simplified chemistry of essential oils, teaching it in courses around the world.

The problem is, the theory is wrong.

For a long answer, keep on reading.

When I started reading books and following Facebook groups and blogs about essential oils and aromatherapy, everybody was talking about phenols, alcohols, aldehydes. It seemed to me that I was the only one who doesn’t understand what they are talking about. Which aldehyde, which phenol, ester of which alcohol and acid?

For many medicinal plants, the mechanisms of their biological effects are not yet understood. That’s why I found it extremely interesting that in aromatherapy, somehow, it is apparently possible to precisely predict the effects of every essential oil you can imagine, as long as they are analysed and the constituents classified according to their chemical structure.

Obviously, I was eager to find out more about such a fascinating subject, and moreover how to put it into practice. I soon figured that the book I would definitely get my answers from was Advanced Aromatherapy (1998) by Dr Kurt Schnaubelt. Who would have known more about the subject than a chemist with more than 30 years of experience with essential oils?

I’ll admit it: for about a month or two, I became Schnaubelt’s fan. Suddenly, everything seemed perfectly clear. You can sketch all the hefty chemistry of any essential oil into a special coordinate system and colour the functional groups represented by the predominant constituents of that oil, almost like in a colouring book. Then, according to specific needs, you combine various essential oils with mutually complementing functional groups into a synergistic personalised blend for therapeutic use. How ingeniously simple is that?

Well, the excitement was soon gone. While covering the holistic approach extensively and criticising conventional science and medicine, the book provides a very limited explanation as to why the specific groups of molecules should work in a particular way. So I started looking for the primary sources of what is today known as the functional group theory/hypothesis (Tisserand 1999). I wanted to understand where the bold assumptions came from, and after that period of excitement, I decided to get to the bottom of the matter.


Let’s take a closer look at the functional group theory of essential oils. It’s based on the assumption that compounds bearing same functional groups have similar chemical properties and will, therefore, exert similar biological effects.

Alcohols, for example, are supposed to have antimicrobial and stimulating properties, esters are anti-inflammatory, spasmolytic and soothing, while ketones have excellent mucolytic, regenerative, analgesic and antiviral properties.

The functional group theory has been used for:

  • Predicting therapeutic benefits of single essential oils and blends
  • Predicting potential toxicity (e.g., ketones are supposed to be neurotoxic, and thus extra caution is needed when using essential oils that contain them)

According to Daniel Pénoël MD (1999), a French medical doctor and naturopath, classification of thousands of compounds into functional groups is a vital step towards understanding therapeutic potential of essential oils, and should thus be the key part of training for their clinical application. Is that really the case?


Probably the first attempt to classify essential oils according to their chemical structure was made by Eugene Charabot and Justin Dupont in the 1920s (Gattefossé 1937/1993). Moreover, they hypothesised that biological effects – including smell perception – are determined by the presence of specific functional groups. They suggested 11 families of essential oils, based on the dominant functional groups.

René-Maurice Gattefossé, the pioneer of aromatherapy who researched clinical application of essential oils, further elaborated on this idea. He suggested classification without regard to terpenes, which would mask or denature properties of other constituents. In his book Aromatherapie (1937/1993) he recommends using deterpenised essential oils as most potent (which is against the today’s standard in aromatherapy).

The idea that structure determines function lived on and was put into clinical practice by researchers and medical practitioners such as Jean Valnet MD and Dr Paul Belaiche (known for using the aromatogram for treatment of microbial infections), who published Traité de phytothérapie et d’aromathérapie in 1979.

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