New contact allergens are formed during vulcanization of rubber

In rubber materials, both natural rubber and synthetic rubber, several different contact allergenic chemicals are added to the batch before vulcanization. These compounds are relevant for investigation of rubber allergy of workers in rubber factories. The number of workers in the rubber industry has declined, owing to increased automation of the process; however, the number of users of rubber products, such as rubber gloves, is increasing. Furthermore, users of finished rubber products are exposed to allergens other than those affecting workers in rubber factories because of chemical reactions during vulcanization between different additives, altering their structures. Our experience with thiuram mono- and disulfides is that during vulcanization, monosulfides are formed from disulfides. We have also seen that in rubber vulcanized with both thiurams and mercaptobenzothiazole compounds, chemicals are formed that contain both thiocarbamate and a mercaptobenzothiazole structure. Two examples of this are dimethylthiocarbamylbenzothiazole sulfide (DMTBS) and diethylthiocarbamylbenzothiazole sulfide (DETBS). The latter is a commercial accelerator with the name Ethylac. In an earlier study in which we patch tested 24 volunteers with a known allergy to thiuram mix and/or mercapto mix, we observed positive reactions to DMTBS (1% petrolatum) and/or DETBS (1% petrolatum) in 20 subjects. So far we have seen positive reactions to either DMTBS or DETBS in two patients who were investigated because of their dermatitis related to the rubber in their swimming goggles. Chemical analysis of the swimming goggles showed them to contain DMTBS and DETBS, respectively. Furthermore, several patients in the Netherlands and Belgium with allergy to their shoes were found to be allergic to DMTBS. Chemical analysis of these shoes has been performed and DMTBS was identified in the rubber lining. The allergy to DMTBS is an example of how a powerful allergen can be formed during vulcanization as a result of chemical reactions between well-known haptens. It also illustrates that chemical investigations of patients' rubber items can uncover the presence of allergens that were not added during manufacturing and therefore never show up in declarations from the producers.