Allergic patch test reactions caused by the rubber chemical cyclohexyl thiophthalimide

Rubber chemicals are among the most common occupational contact sensitizers. The most common rubber sensitizers are thiurams, thiazoles, carbamates and paraphenylenediamine derivatives. Here we present data on a less-well-known rubber chemical, N-(cyclohexylthio)phthalimide (CTP; CAS 17796-82-6). This chemical is currently the most widely used vulcanization retarder, but data on allergic contact dermatitis caused by CTP are lacking. We conducted a survey of 310 patients who had been patch tested with 30 rubber chemicals including CTP. 11 (3.5%) showed an allergic patch test reaction provoked by CTP, and 9.0% by thiurams. 4 of the patients reacted only to CTP and not to other rubber chemicals, whereas the other 7 concomitantly reacted to other rubber chemicals. After analyzing the patch test data of these 11 patients, it was concluded that CTP probably did not cross-react with the other rubber chemicals. Therefore the patch test results may indicate independent sensitization to CTP and other rubber chemicals. Because very little data on the components of rubber chemicals in rubber products are available, the source of the putative sensitization to the rubber vulcanization retarder CTP is unknown.