The outcome of 9 years of consecutive patch testing with 4,4'-diaminodiphenylmethane and 4,4'-diphenylmethane diisocyanate.

Two outbreaks of allergic contact dermatitis caused by isocyanates at two companies in southern Sweden initiated a research project focusing on contact allergy to isocyanates. Within the project, there was an interest in determining how often contact allergy to the most common isocyanate, diphenylmethane-4,4'-diisocyanate (4,4'-MDI), occurred. To determine and compare the occurrence of contact allergy to 4,4'-MDI, its corresponding amine 4,4'-diaminodiphenylmethane (4,4'-MDA), and polymeric diphenylmethane diisocyanate (PMDI) in a Swedish and a Belgian study population. Patients and method. The study population consisted of 6190 consecutively patch tested dermatitis patients: 5690 patients from Malmö, Sweden, and 500 patients from Leuven, Belgium. Patch test results were analysed and compared. None of the Belgian patients reacted positively to 4,4'-MDI, but 5 Swedish patients did. Contact allergy to 4,4'-MDA was more common in the Belgian patients than in the Swedish patients: 3.6% and 0.9%, respectively. This could possibly be explained by the fact that the prevalence of p-phenylenediamine allergy was higher in the Belgian population. The prevalence of contact allergy to 4,4'-MDI, 4,4'-MDA and PMDI is not high enough to justify their inclusion in any baseline series. Isocyanate allergic individuals should be detected by aimed testing with an isocyanate series and work materials.