The sensitizing capacity of atranorin.

The allergenic potential of the aromatic lichen substance atranorin has been investigated by means of the guinea pig maximization test of Magnusson & Kligman. Sensitivity was induced in 30% of the animals, which corresponds to a moderate allergenic capacity (grade III). This is in agreement with the clinically-observed frequency of 1.5% among our patients. A modified photoallergy test on the same animals was performed, but irradiation did not increase the number of positive reactions. 4 patients with proven contact sensitivity to atranorin, evernic, usnic or physodic acid, were examined with different dilutions from 0.001 to 0.1%. Irradiation of the test series did not provoke any clear-cut photoallergic reaction.