Autoxidation of linalyl acetate, the main component of lavender oil, creates potent contact allergens.

Fragrances are among the most common causes of allergic contact dermatitis. We have in previous studies shown that linalool, present in lavender oil, autoxidizes on air exposure, forming allergenic oxidation products. Oxidized linalool was found to be a frequent cause of contact allergy in a patch test study on consecutive dermatitis patients. Linalyl acetate, the main component of lavender oil is commonly used as a fragrance chemical in scented products. Because of structural similarities, linalyl acetate should also be susceptible to oxidation on air exposure, forming similar oxidation products as linalool. The aim of the present study was to investigate the autoxidation of linalyl acetate and the influence of oxidation on its sensitizing potency. Analyses were performed using gas chromatography, nuclear magnetic resonance spectrometry and mass spectrometry. Sensitizing potencies of compounds were determined using the local lymph node assay (LLNA) in mice. Analyses showed that the content of linalyl acetate decreased over time on air exposure and other compounds were formed. Hydroperoxides, an epoxide and an alcohol were identified as oxidation products from linalyl acetate. In the LLNA, linalyl acetate of high purity showed a weak sensitizing potency (EC3 25%). Autoxidation increased the sensitizing potency of linalyl acetate, and a 10 weeks oxidized sample gave an EC3 value of 3.6%. As for linalool, the hydroperoxides were shown to be the oxidation products with the highest sensitizing potency. It is concluded that autoxidation of the weakly allergenic linalyl acetate leads to formation of allergenic oxidation products.