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  1. #1

    Default The Trouble With Theories About The Oxidation of Essential Oils.

    This is from Tony Burfield from Crop Watch:

    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. 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 Hostyneck & Maibach’s on geraniol & linalool (Hostyneck & Maibach 2007a; Hostyneck & 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 Hostyneck & 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. Hostyneck & 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.

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

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

    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.

    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.

    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.

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

    Hostyneck J.J. & Maibach H.I. (2008) “Allergic contact dermatitis to linalool.” Perf. & Flav. 33 (July 2008), 52-56.

    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.

    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.
    Last edited by Grant; 8th February 2009 at 06:08 PM.

  2. #2

    Default Re: The Trouble With Theories About The Oxidation of Essential Oils.

    You can't just post it Grant, you have to give a thorough explanation, analysis and commentary including sourced reference to the comtemporay literature. Demonstration of knowledge of related work currently being undertaken would also be credited.

    But really...phew, I just about made it through that. I support cropwatch and their position. Gimme my citrus oils, inform me as to what they *might* do to me and I'll make up my own mind.
    "Don’t try to be original. Be simple. Be good technically, and if there is something in you, it will come out. ” - Henri Matisse.

    "Wear R de Capucci" - Hirch Duckfinder


  3. #3
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    Default Re: The Trouble With Theories About The Oxidation of Essential Oils.

    What I find ironic is that this research, and more like it, could actually save the natural fragrance industry. I find this just another demonstration that knowledge of the truth by all parties as early as possible is the fastest path to everybody's happy future. Ignorance is not bliss - it is either deception, or self-deception.

    As the author of the thesis concluded:

    The results presented in this thesis could be used to reduce the risk of contact sensitization to fragrances and could contribute to a scientific basis for political decisions regarding the regulation of the use of fragrances in consumer products.
    First, commenting on the fact that it's a thesis. Tony Burfield has an excellent point that a thesis is only gated through supervising academicians, and thus doesn't have the same pedigree as journal-published work. That much said, it is based on such, and need not be any less true. Comments by the author may be a bit less nuanced since not refereed, but the author may speak more honestly overall, or with a certain bluntness. I only skimmed it, but it looks like a nice, normal Ph.D. thesis to me. I agree with Tony that there need to be many such studies, although I suspect they will show roughly the same thing.

    There are probably some finer points that I'm missing, not being in the industry, but the bottom line is that this work shows that, whatever the actual sensitization characteristics of the studied fragrance terpenes, it can be shown that standard natural oxidation products can be made, and are, in fact, sensitizers. This may be like the finding of oxidized polycyclic aromatic hydrocarbon species as the source of PAH carcinogenicity. It's cause for celebration - not worry.

    I personally don't think that there should be any fuss in the industry. The structural overlap between natural oils and semi-synthetic or synthetic fragrances is huge. The Achilles heel of naturals is complexity of mixture, and the Achilles heel of synthetics is non-biodegradability. Between the Scylla of oxidative byproducts when components are (bio)degradable, and the Charybdis of ecological persistence when they aren't, the good ships Natural and Synthetic may still be distinguishable, but not by much.

    Assuming that such substances are behind any kind of sensitization in the real world, then the more we know about this stuff, the sooner we can find ways to stop it - and hopefully without any effect on the perfumer's palette. If the work helps bring about the evaluation and study of both natural and synthetic antioxidants which will one day prevent sensitization, then it has to be a good thing for everybody.

    I won't take a stand on whether there is too much regulation overall. I just hope that any and all regulation is sensible. I'm with Hirch - we want to be informed AND fragranced. Big Sister's warnings not to have too much fun are duly noted.

    "When good perfume is criminalized, only criminals will sell perfume. Bad perfume."
    Currently wearing: Wanted by Azzaro

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