Identification of 15-hydroperoxyabietic acid as a contact allergen in Portuguese colophony

15-Hydroperoxyabietic acid (15-HPA) has been isolated from Portuguese colophony of the gum rosin type and identified as its methyl ester. The structure of the compound was elucidated using UV, IR, NMR and mass spectrometry. 15-HPA methyl ester was found to be an elicitor when tested in colophony-sensitized guinea-pigs. The sensitizing capacity was verified in the same species and 15-HPA methyl ester was considered to be a strong allergen. The eliciting potential was also verified in patients with known allergy to colophony. The Portuguese gum rosin investigated contained approximately 1% of 15-HPA. Based on its allergenicity and the amounts isolated, we conclude that 15-HPA is a main contact allergen in Portuguese gum rosin.