Isothiocyanates are important as haptens in contact allergy to chloroprene rubber.

Thiourea compounds are degraded to isothiocyanates, which are generally strong or extreme sensitizers, thus acting as prehaptens. This process occurs in both chloroprene rubber products and patch-test preparations. Positive reactions to phenyl isocyanate indicate cutaneous metabolism, as the only known source of exposure to phenyl isocyanate is through bioactivation of diphenylthiourea.