Allergenicity of fragrance terpenes with respect to their degradation/oxidation over time was studied. The prevalence of contact sensitisation to the oxidative degradation products of monoterpenes frequently used as fragrance chemicals (limonene, linalool, caryophyllene, myrcene) in patients with suspected fragrance allergy and in patients with hand eczema due to contact with scented household products was investigated. The aim was also to identify the potential allergenic oxidation/degradation products.
The fragrance chemicals linalool, caryophyllene and myrcene easily autoxidise when air exposed. Experimental studies have shown that these terpenes themselves are not allergenic. To test if autoxidation can cause a change in the allergenic activity, the oxidised terpenes were diluted in petrolatum and patch tested in consecutive dermatitis patients in 6 European dermatological clinics. The preparations tested were: oxidised linalool, a hydroperoxide fraction of linalool, oxidised caryophyllene, caryophyllene oxide and oxidised myrcene.
Positive reactions were observed in 1.8% of in total 1343 patients tested. Most reactions were seen to oxidised linalool (1.2%) and its hydroperoxide fraction (1%). This could, at least partly, be explained by a greater usage of linalool (lavender oil) compared to the usage of the other fragrance chemicals studied. The reaction pattern and the frequency of positive results differed between the different clinics. A significant correlation with contact allergy to other fragrance materials was observed.
Results showed that the observations from the limonene study also apply to other fragrance terpenes. It further implies that the EU regulation regarding limonene (classified as a sensitizer by skin contact R43- due to formation of allergens when air exposed) can be applicable on the chemicals studied, especially on linalool.