The Trouble With Theories About The Oxidation of Essential Oils

by Tony Burfield Feb 2009.

Judging by the response from Cropwatch supporters, many of you may have already read about a doctoral thesis and remarks made by Lina Hagvall, distributed via the cosmetics trade press. Many professionals have found the reported remarks condescending, as we are well aware and may have a wider understanding of the context of oxidized aroma materials than the source of the remarks. But I digress. The thesis in question is entitled “Formation of skin sensitizers from fragrance terpenes via oxidative activation routes: Chemical analysis, structure elucidation”, and Katie Bird (Bird 2009) recently covered the story for Cosmetics Design Europe, although, as with any news knocking natural products, the article is being very widely circulated on websites dealing with health interest and other matters. Many of us have found the Bird-penned article makes for confusing reading: for example what is ‘geraniol oil’? A better recourse is maybe to download the thesis itself from the University of Gothenburg website at http://gupea.ub.gu.se/dspace/handle/2077/18951. You will then be able to gather that the thesis is primarily concerned with the consideration of substances without contact allergenic properties, but which can be activated either via autoxidation in contact with air, or via cutaneous metabolism, to reactive products which can cause contact allergy. Primarily the study looks a five published articles for which the author has had a major involvement, studying the oxidation of geraniol, geranial (a conformational isomer of citral), linalool, linalyl acetate & lavender oil. For convenience these articles are referenced below (Hagvall et al. 2007; Hagvall et al. undated; Hagvall et al. 2008; Skold et al. 2008; Hagvall et al. 2008a).

If I were one of Hagvall’s invigilators, I would have insisted on a re-write of a number of parts of the thesis, where the science as presented is dubious, incomplete or, most importantly, does not present an accurate overview of the topic. Some knowledge of industrial practices would have aided its general acceptability as well, and a collection of these points will constitute a future article from this author.

Overall this author is not saying that the elucidation of underlying mechanisms whereby oxidized essential oils, which may be the cause of type IV allergy and acute contact dermatitis, is not important. But an overview to enable to put this work in perspective is importantly missing. Further, the mention of Axel Schnuch’s work (Schnuch et al. 2007) is selective, and a major omission to include the toxicological reviews of Hostynek & Maibach’s on geraniol & linalool (Hostynek & Maibach 2007a; Hostynek & Maibach) is almost unforgivable, however inconvenient their conclusions to Hagvall’s work. The reader is thus left to form his/her own independent opinion on the relevance of the study, especially against a background of an increasing number of published studies on the anti-oxidative properties of essential oils, the declining concentrations & use of essential oils in fragrances generally, the use of cold-storage & nitrogen-blanketing (amongst other measures) to prevent the oxidative deterioration of stored essential oil and natural isolate ingredients, and the addition of anti-oxidants, UV-filters and stabilizers to finished fragrances & cosmetics to extend shelf-life One is also tempted to mention that a major contributor to the cost of the studies was RIFM, a primary instigator to the culture of toxicological imperialism which has overtaken the regulation of cosmetics/fragrances in the West.

How does this thesis change anything? The lack of evidence of a clear cause-effect relationship between geraniol and linalool and cases of allergic contact dermatitis has been previously emphasized by Hostynek & Maibach (2004 & 2008), and Cropwatch would guess from its’ own experience that adverse end-user effects would tend to support the same conclusion for lavender oil. Hostynek & Maibach (2008) also comment on the relative stability of linalool, its low oxidation rate kinetics and speculate negatively about how readily linalool would oxidize in fragrances & cosmetics, as well as low consumer exposure levels to the ingredients. Great store seems to have been put on the Hagvall thesis by IFRA/RIFM juggernaut, but considering the importance of the sensitiser issue to the perfumery trade, and its impact on the use of natural ingredients in perfumery, the sponsoring of just one researcher to look (mainly) at the oxidation of geraniol & lavender oil seems an exceptionally disproportionate response to the problem. Unless of course you believe that RIFM sees the future of perfumery as entirely synthetic.

Cropwatch is trying to work towards the sponsorship of toxicological research which emphasises a risk/benefit approach towards the elucidation of the safety of natural products - otherwise we will all drown in a sea of over-cautious toxicological negativity, which, it is becoming clear, has little relevance in terms of safety risks presented to the general public from natural-product containing products.

References.

Bird K. (2009) “Essential oils can become allergens on contact with air and skin, says researcher.” Cosmetics-Design Europe 5^th Feb 2009. Link

Hagvall L. (2009) “Formation of skin sensitizers from fragrance terpenes via oxidative activation routes: Chemical analysis, structure elucidation.” PhD Thesis University of Gothenberg. Link

Hagvall L., Bäcktorp C., Svensson S., Nyman G., Börje A. & Karlberg A-T. (2007) “Fragrance Compound Geraniol Forms Contact Allergens on Air Exposure. Identification and Quantification of Oxidation Products and Effect on Skin Sensitization.” Chem. Res.Toxicol. 20, 807-814. Link to HTML Version

Hagvall L., Börje A. & Karlberg A-T. (date unknown) “Autoxidation of Geranial.” (Unpublished?) Manuscript.

Hagvall L., Baron J. M., Börje A., Weidolf L., Merk H. & Karlberg A-T (2008) “Cytochrome P450 mediated activation of the fragrance compound geraniol forms potent contact allergens.” Toxicol. Appl. Pharmacol. 233, 308-313. Link to Abstract

Hagvall L., Sköld M., Bråred-Christensson J., Börje A. & Karlberg, A.T. (2008a) “Lavender Oil Lacks Natural Protection Against Autoxidation, Forming Strong Contact Allergens on Air Exposure.” Contact Dermatitis 59, 143-150. Link to Abstract

Hostynek J.J. & Maibach H.I. (2004) “Is there evidence that geraniol causes allergic contact dermatitis?” Exogenous Dermatology 3(6), 318-331. Link to Abstract

Hostynek J.J. & Maibach H.I. (2008) “Allergic contact dermatitis to linalool.” Perf. & Flav. 33 (May 2008), 52-56. Link to Excerpt

Schnuch A., Uter W., Geier J, Lessmann H. & Frosch PJ. (2007) "Sensitization to 26 fragrances to be labelled according to current European regulation. Results of the IVDK and review of the literature." Contact Dermatitis 57(1), 1-10. Link to html version

Sköld M., Hagvall L. & Karlberg A-T (2008).”Autoxidation of linalyl acetate, the main component of lavender oil, creates potent contact allergens.” Contact Dermatitis 58, 9-14. Link to Abstract

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