Is ascaridol het contact-allergeen in tea tree oil?

Tea tree oil is used as a natural remedy, but is also a popular ingredient in household and cosmetic products. Oxidation of tea tree oil may result in degradation products, such as ascaridole, which may cause allergic contact dermatitis. We investigated the prevalence of sensitization to ascaridole, the optimal patch test concentration and we studied co-sensitization of ascaridole and oxidized tea tree oil. A total of 290 patiënts with eczema were patch tested with ascaridole 1%, 2% and 5% in petrolatum. Ascaridole 2% seems to be the most favorable patch test concentration based on the ratio of positive (5.5%), irritant (1.7%) and doubtful (4.1%) reactions. Six patients showed a positive reaction to oxidized tea tree oil. All patients with a positive reaction to tea tree oil showed a positive reaction to ascaridole. This finding suggests that ascaridole is contact allergen in tea tree oil. A total of 24 patients showed a positive reaction to ascaridole without a positive reaction to tea tree oil. Six out of these 24 patients were exposed to tea tree oil en developed eczema after using products containing tea tree oil. Patch testing with ascaridole elicits clinically relevant positive reactions, which are missed by patch testing with tea tree oil alone.