Book Reviews
Book 31

Essential Oils in Colour – Caddy Classic Profiles by Rosemary Caddy - Amberwood Publishing Ltd (1997) 

ISBN: 1-899308-14-8
…and its place in the Functional Group Hypothesis.

Copyright © Tony Burfield Dec 2004.


The Caddy Classic Profiles are basically a series of brightly coloured pie-charts of 90 essential oils commonly used in aromatherapy, broken down according to the proportions of the functional groups of the constituent molecules. The functional groups are divided down into esters (blue), aliphatic aldehydes (indigo), ketones (light blue), sesquiterpenes (green), lactones & coumarins (dark grey-green), oxides (canary yellow), acids (chrome yellow), aromatic aldehydes (brown), monoterpenes (orange), alcohols (red) and phenols & phenolic ethers (purpley-red). Each essential oil gets a one-page entry in the book, which includes an interpretation of the pie-chart.

On page 1-7 of the sixteen page introduction, Caddy refers to Pierre Franchomme’s work where chemical constituent molecules of the essential oils were sprayed between “electromagnetic” plates.  According to Caddy, the findings supposedly show an ordering of chemical families according to the “solubility (presumably referring to lipophilicity/hydrophilicity) and magnetic attraction” (presumably relating to electrophilicity/nuclephilicity or electron receiving/donating abilities) of the families. Few with any knowledge of electrochemistry would think this work has any redeeming value - as I have remarked elsewhere, considering the actual specifications of the components of the circuitry used, the experiment is more likely to have been measuring static, or, with any luck at all, have been tuning into to amplitude fluctuations in the signals of Radio Paris.

Nevertheless, regarding the component ordering, Caddy decided aliphatic aldehydes and ketones generate “more negative particles” – hence the blue colouring, whereas oxides, acids, aromatic aldehydes, monoterpenes, alcohols and phenols generate “more positive particles” and are coloured yellow to red. “Neutral particles” represented by sesquiterpenes, lactones and coumarins are coloured in shades of green. 

Some background.

Franchomme’s hypothesis that the inherent properties of functional groups of the major constituent molecules of essential oils could explain the therapeutic properties of essential oils continued in the teachings of his own French school, and he influenced other aromatherapy teachers such as Rodolphe Baltz, who describes the therapeutic properties of over 200 essential oils in The Healing Power of Essential Oils. The theory was further advanced by Franchomme and Penoel’s major pharmacological work in French - never translated into English - l'Aromatherapie Exactement pub. Jollois (1990) ISBN 2-87819-001-7. By now a number of French & English schools were teaching the   principles of the hypothesis, and the Franchomme school of thought was further advanced by Kurt Schnaubelt (of the Pacific Institute of Aromatherapy) in the USA who went on to market the very successful Advanced Aromatherapy  published by Healing Arts Press  (English translation in 1998) ISBN 0-89281-743-7, which describes the hypothesis in a highly graphical manner over pages 51-95. In a key statement on page 52, Schnaubelt acknowledges Franchomme’s contribution to aromatherapy which he describes as “…to acknowledge the impact that the tendency to donate or subtract electrons has on the properties of an essential oil component”.

The problem is, that in the simplistic form that the hypothesis tends to get reduced to, by some aromatherapy teachers – aldehydes are anti-inflammatory, ketones are toxic etc. etc. – and this is, in my view, complete bollocks. I was later to review the Schnaubelt book with S. Sheppard-Hanger in the IJA 9(3) p 139, but previously Robert Tisserrand, then editor of the IJA, threw down the gauntlet to Schnaubelt in the form of an editorial in IJA 9(2), challenging him to offer one shred of scientific evidence that the “theory” actually works. Schnaubelt subsequently gave a somewhat weak reply in IJA 10(2) p 62-3 suggesting that the true origin of the hypothesis (rather than theory) lay originally with the chemical classifications by the French fragrance companies Charabot & Dupont. He further implied that the functional hypothesis does not explain all the properties of essential oils, but is observed more favourably in monoterpenoids where lipophilicity and electrophilicity/nucleophilicity can be important. Schnaulbelt conceded that the “one-dimensional pharmacology” involved (with the functional group hypothes) was limiting, and that aromatherapy conceivably works through the action of hundreds of components, including the minor ones. It’s a pity that these admissions were not included in Advanced Aromatherapy – instead the footnotes to Franchomme’s original work remark that the results are not undisputed, but he argues that the model is convincing and that they (the results) “…establish a sensible if somewhat rough system of oils and their qualities which has proven itself empirically over the past ten years”. 

Penoel also defended the molecular functional approach in IJA 9(4) p162-3 conceding the reportage of the ‘molecular approach’ had resulted in an oversimplified and generalised approach. For example, he remarks that the statement that all ketones are neurotoxic is now not agreed. However Penoel remarked that the approach offered more advantages than drawbacks. Penoel goes on to distinguish between three systems: single oils, horizontal functional molecular synergies between essential oils (blending oils with similar functional groups) and vertical functional molecular synergies (blending oils with different functional groups). 

With all this discredit as a background, it is surprising that the functional group hypothesis still remains a central part of aromatherapy dogma today, to the extent that this little popular high street book was muted as a set book for aromatherapy students to study, in the initial proposal by the collective wisdom of the Syllabus Committee of Aromatherapy Consortium 2004. What hope for aromatherapy if its would-be regulators do not keep up with events in modern aromatherapy thought?

Back to Caddy

This poorly referenced book was reviewed in 1998 by Robert Tisserand (IJA 9(1) p43-44) who severely criticised it, concluding, "nature is far more complex than this pseudo-scientific work would have us believe".

Dipping into the pages at random, under lavender true (p 42), we find it incorrectly described as Lavandula augustifolia (its angustifolia) and is incorrectly described as being distilled from the stalks (lavender stalk oils are harsh, and inferior to ‘normal’ oils from the flowering tops). The oil is mentioned as possessing stimulant (?) & sedative properties, which, double checking with Tisserand’s review (referenced above), was also queried by him. Worse than this in the introduction on 1-5, the same oil is featured where “the large proportion of alcohols will have good stimulating properties…”. The basis for this seems to be that in section 1-14 of the book, alcohols are said to be stimulant. Yet linalol is clearly a well-proven CNS depressant… Tisserand picks up on the fact that Caddy adds the rider in part 1-14 that some sesquiterpenols and aromatic alcohols may be calming. However linalol is not an aromatic alcohol! So we see that with one of the most heavily used aromatherapy raw materials, Caddy’s theories are already in trouble.

If the hypothesis were to be given the best chance to demonstrate that it works – it should surely be in those cases where a single component dominates the composition of the oil. We could imagine that wintergreen oil (97% methyl salicylate), rosewood oil (to 95% linalol), palmarosa oil (to 85% geraniol), cinnamon leaf oil (86% eugenol) could provide examples here. However according to Caddy we see rosewood and palmarosa oils as  stimulants, and cinnamon listed as aphrodisiac (I regret to inform readers that there is no scientific evidence for this!).

Several urban myths are repeated in the book – that for example Rosemary and Fennel oils should not be used with epileptic patients – although there is no proof that this is so. Cedarwood oils Virginian or Texas should be avoided in pregnancy – there is currently no scientific basis for this either. Lemongrass oils (East and West India) are reported to contain ‘aliphatic aldehydes’ – a confusing term which is better replaced by acyclic monoterpinic aldehydes to avoid confusion with straight chain aliphatic aldehydes such as 1-decanal.  Where there should be appropriate hazard/risk cautions – these are missing – e.g. for Cade oil (i.e. only the redistilled oil should be used), for Hyssop oil  (toxicity) or for Grapefruit oil (said to be non-photo-toxic whereas there is a quantifiable risk).

The most unfortunate part of the book is the risk of literal translation of the general properties of the chemical families for the specific oils in question, e.g. all lactones and coumarins are calming, sedative, uplifting (nervous system), all lactones and coumarins are anticoagulant, lower the blood pressure, are decongestant (circulation and immune system). Although there is a qualifier (“individual chemical constituents may exhibit some of the characteristics of the family they belong to…”) one is left wondering why bother with the system at all.

Future Direction for the Hypothesis

Although Schnaubelt, Penoel and others vaguely refer to molecular structures attached to functional groups as being important, the only person to impress me in advancing the functional group hypothesis further is probably Joy Bowles. If I remember correctly when I met her a few years back, Bowles indicated that the functional hypothesis is far more credible if specific molecular structures associated with, and in proximity to the functional group are also considered. I agree with this, since for example we know that certain sesquiterpene lactones are sensitising because they carry an alpha-methylene butrylactone structure which is held in common with other sensitising substances occurring in costus oil, laurel leaf oil, feverfew oil etc.   This is getting a bit complicated....but may better fit the known characteristics of  certain essential oil properties. Paraphrasing Penoel’s comments in the article quoted above, about a the relevance of a holistic approach to essential oil therapeutics, and the comments by Tisserand complaining that the functional group hypothesis in any case does not account for synergistic and antagonistic effects of essential oil components, probably means that the whole hypothesis is now credited with limited value. It is far more important to establish the therapeutic properties of essential oils per se, without their attempted interpretation by simplistic theories.