The Scandinavian multicenter photopatch study 1980-1985: final report.

At 16 different dermatology clinics in Scandinavia from 1980-1985, photopatch testing was performed on 1993 patients with suspected photodermatosis. The collective results are presented in this article. The most common cause of sun-related dermatosis was polymorphic light eruption (PLE) (38%), while secondary aggravation of pre-existing skin diseases was established in 16% of the patient group. Photocontact dermatitis (11%) and contact dermatitis (10%) were responsible for 274 and 369 positive test reactions (respectively) on photopatch testing using the SPDRG standard series. Musk ambrette and para-aminobenzoic acid were the leading photosensitizers, while perfume mixture, balsam of Peru and lichen mixture were the most frequent causes of contact sensitivity. The principal photoallergens and contact allergens in the PLE, persistent light reaction and actinic reticuloid groups are discussed, together with the problems, risks and possible mechanisms of induction of photosensitization in these patients. The incidence, causes and diagnostic and therapeutic implications of secondary sunscreen sensitivity in these groups are also addressed.