Pigmented contact dermatitis from azo dyes. I. Cross-sensitivity in humans.

Eight patients suffering from pigmented contact dermatitis caused by the commerical Brilliant Lake Red R were patch tested with purified Sudan I and its several chemical analogues. Positive reactions were observed to Sudan I, Orange SS, Brilliant Lake Red R, Vacanceine Red, Yellow OB and Sudan II. Negative tests were obtained with Toluidine Red, Permanent Orange, Lithol Red and Sudan III. We found that the commerical Brilliant Lake Red R which has been said to be most important causative agent of pigmented contact dermatitis, contained Sudan I as a major impurity. The patients reacting to Brilliant Lake Red R always gave a positive reaction to Sudan I, but those reacting to Sudan I did not always give a positive reaction to Brilliant Lake Red R. This suggests that Sudan I is a potent sensitizer and may induce contact sensitivity and Brilliant Lake Red R itself is a weak sensitizer or a cross-reacting substance.