Reactions causing reactions: allergic contact dermatitis to an isocyanate metabolite but not to the parent compound

Industrial use of isocyanate resins rarely causes allergic contact dermatitis. We report a patient who developed allergic contact dermatitis to a transitory chemical breakdown product of the isocyanate 4,4'-diphenylmethane diisocyanate (MDI), diaminodiphenylmethane (DDM), although he was not sensitized to the suspected parent compound MDI.