[Allergic contact dermatitis caused by Asteraceae. Identification of an 8,9-epoxythymol-diester as the contact allergen of Arnica sachalinensis].

A pharmacist developed an allergic contact dermatitis while working with Arnica sachalinensis. Patch testing with sesquiterpene lactones was negative. The contact allergen of A. sachalinensis was identified as 10-acetoxy-8,9-epoxy-thymol-isobutyrate. This compound, or structurally related 8,9-epoxythymol-diesters, are often found in Asteraceae. In addition to sesquiterpene lactones, epoxythymol-diesters should be considered as contact allergens. Cross reactions between the two groups of compounds are not expected and could not be demonstrated in our patients.