Even natural perfumes may cause allergies

Hypersensitivity to perfumes is the most common contact allergy in adults. Research at the University of Gothenburg, Sweden has demonstrated that even natural aromatic oils, which many deem harmless compared to synthetic perfumes, may cause allergic reactions.

Roughly one in five adults in northern Europe is believed to suffer from contact allergy to one or more chemicals. The most common is nickel allergy, but many people also suffer from contact allergy to perfumes - even perfume substances that at first glance appear to be harmless can cause allergic reactions. New eczema-provoking allergens are formed by reaction with acid in the ambient air (known as autoxidation) or with skin enzymes.

Natural Aromas not Safer

Modern society commonly regards anything that comes from nature as being healthier and less dangerous. Where it concerns natural aromas, known as essential oils, many manufacturers believe that natural antioxidants in these oils offer protection against autoxidation thus making them safer and longer lasting than artificial perfumes. Research at the University of Gothenburg shows this is not the case.

Reaction with the skin

Lina Hagvall, a researcher at the University of Gothenburg's Department of Chemistry, has examined natural lavender oil in her thesis. Her results show that essential oils do not prevent the formation of allergenic substances through reactions with acid; something which had not previously been possible to confirm. Hagvall's thesis also examines geraniol, a common constituent of perfumes such as rose oil. The study shows geraniol by itself to be only slightly allergenic. However through autoxidation and reaction with skin enzymes, the substance is activated and becomes the closely related allergen geranial. This is the first time these activation pathways have been demonstrated for the substance.

More perfumes can be allergene

It is important to investigate how perfumes react with air or on skin. Lina Hagvall's thesis concludes that such risks must be factored into health risk assessments of chemicals relating to contact allergy. The thesis also demonstrates that more perfumes than previously believed can be activated into allergens, and that more studies should be done to increase knowledge within the field and thus reduce the number of eczema cases.

Hagvalls thesis, Formation of Skin Sensitizers from Fragrance Terpenes via Oxidative Activation Routes. Chemical analysis, Structure Elucidation and Experimental Sensitization Studies was defended on the January 30th. The supervisor was Ann-Therese Karlberg, professor of dermatochemistry and head of the research platform Göteborg Science Centre for Molecular Skin Research at the University of Gothenburg.

Abstract:

The work presented in this thesis emphasizes the importance of considering oxidative activation in the toxicity assessment of fragrance chemicals. Compounds without contact allergenic properties can be activated either via autoxidation in contact with air or via cutaneous metabolism to reactive products which can cause contact allergy. It is important to prevent sensitization as the immunological memory formed in the development of contact allergy persists throughout life. The investigation of compounds susceptible to oxidative activation, thereby forming sensitizing compounds is important in the work of prevention of contact allergy. The overall aim of this thesis was to investigate mechanisms of activation via autoxidation and metabolism of single fragrance compounds and essential oils, and to study the impact of this activation on the contact allergenic activity. The oxidative activation via autoxidation and cutaneous metabolism of the fragrance compounds geraniol and geranial was studied. It was shown that both compounds were susceptible to autoxidation, forming oxidation products with increased sensitizing capacity compared to the original compound. The oxidation products of geraniol were formed by two separate pathways, corresponding to autoxidation of each of the two double bonds in geraniol, respectively. Hydroperoxides, which previously have been identified as the most important sensitizers in the oxidation mixtures of air-exposed fragrance compounds could not be detected in air-exposed geranial. Instead, a sensitizing epoxide was detected. Geraniol and geranial were also activated metabolically. Many of the metabolites identified were also present in the autoxidation mixtures. The autoxidation of lavender oil was studied in order to investigate if essential oils possess a natural protection against autoxidation. The results were compared to the results from the autoxidation studies of linalyl acetate and linalool, the main components of lavender oil. It was found that the autoxidation proceeded in the same way in both the pure samples and the lavender oil, and that sensitizing oxidation products were formed in both cases. The most important sensitizers formed were hydroperoxides of linalool and linalyl acetate. This thesis adds important information on routes of autoxidation as well as on the relationship between metabolic and air induced activation of non- or weakly sensitizing compounds to sensitizers. The results presented here indicate that other fragrance terpenes could be susceptible to oxidative activation via autoxidation or cutaneous metabolism. This should be considered in the risk assessment of fragrance chemicals.