Carvone: an overlooked contact allergen cross-reacting with sesquiterpene lactones?

The terpene l-carvone is one of the main constituents of spearmint oil. The sensitizing potential of l-carvone has been considered low, but it has occasionally caused contact allergy in users of spearmint toothpaste and chewing gum. l-Carvone is also an oxidation product of d-limonene that occurs in solvents used increasingly in industry. We included l-carvone 5% pet. in the standard patch test series. In the 1st year, 541 patients were tested and 15 (2.77%) had positive, and 12 doubtful positive (?+) reactions to l-carvone. The strongest reactions were observed in 9 patients with concomitant Compositae sensitivity. The key clinical features and other contact allergies of the patients are presented. When re-testing with l-carvone in the same or lower concentrations, only 2 out of 8 patients had positive reactions. Possible reasons for this discrepancy are discussed in terms of cross-reactions, concomitant sensitization, excited skin syndrome, irritancy and facilitated immunological response.