Background: Lavender oil is an essential oil frequently used as a fragrance ingredient and in traditional herbal medicine. We have previously studied the effect of air oxidation on the skin sensitizing potency of the monoterpenes linalyl acetate, linalool and β-caryophyllene, the main constituents of lavender oil.
Objective: The aim of this study was to investigate if the autoxidation observed for the single synthetic terpenes, resulting in strong contact allergens, will take place also in lavender oil.
Methods: Lavender oil was exposed to air and the autoxidation was followed by chemical analysis. The sensitizing potency before and after air exposure was investigated in mice using the local lymph node assay. Patients with patch test reactions to oxidized linalool were tested to investigate if air-exposed lavender oil could elicit dermatitis in these individuals.
Results: The terpenes oxidized in air-exposed lavender oil at the same rates as the pure compounds exposed to air, and the same oxidation products were identified. The sensitizing potency of lavender oil increased accordingly on air exposure. Patch testing showed positive reactions to air-exposed lavender oil and also to oxidized linalyl acetate in patients with contact allergy to oxidized linalool.
Conclusion: This study shows that lavender oil lacks natural protection against autoxidation, and that air-exposed lavender oil can be an important source of exposure to allergenic hydroperoxides.