[Contact allergy to mephenesin].

A case of erythema multiforme-like allergic contact dermatitis due to midysalb, an ointment containing mephenesine is described. Patch testing showed marked sensitization to mephenesine, with positive reactions to different dilutions down to 0.1%. It is unlikely that the weak reaction to a further component, ethylene glycol monosalicylic acid ester, is responsible for the allergy. There are several other reports in the literature, so that mephenesine must be classed as one of the few allergens that cause reactions reminiscent of erythema multiforme.