A case of erythema multiforme-like allergic contact dermatitis due to
midysalb, an ointment containing mephenesine is described. Patch testi
ng showed marked sensitization to mephenesine, with positive reactions
to different dilutions down to 0.1 %. It is unlikely that the weak re
action to a further component, ethylene glycol monosalicylic acid este
r, 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.