Phosgene (chlorophenyl)hydrazones, strong sensitizers found in yellow sweaters bleached with sodium hypochlorite, defined as causative allergens for contact dermatitis by an experimental screening method in animals

12 young men developed allergic contact dermatitis from wearing yellow cotton sweaters. We attempted to identify the causative agents by an experimental screening method in animals. Guinea pigs were sensitized with an acetone extract of the sweater material, by means of the guinea pie maximization test (GPMT). Active ingredients were then separated from the extract, by step‐by‐step patch test screening of chromatographic fractions in the guinea pigs, and finally analyzed by gas chromatography‐mass spectrometry (GC‐MS). Although there were 2 allergens with important activity (1 in the fraction eluted from the silica gel column with hexane, and 1 in the methanol fraction), the present study is focussed on the fat‐soluble allergens in the hexane fraction. GC‐MS analysis revealed that 4 kinds of phosgene (chlorophenyl) hydrazones (PCPHs) were present in the hexane fraction. PCPHs prepared in our laboratory showed strong eliciting activities, not only in the guinea pigs sensitized with the extract, but also in a male volunteer sensitised by exposure to a yellow sweater during irritancy testing. Phosgene (2,5‐dichlorophenyl)hydrazone, which Was the main component, among the PCPHs found in the sweater, sensitized guinea pigs even at the 1 ppm level. From these results, we conclude that PCPHs were one of the allergens responsible for the cases.