Photoallergic contact dermatitis

PURPOSE: To determine whether photoallergic contact dermatitis is as uncommon as it is usually considered to be and to review the associated clinical features. METHODS: We reviewed the literature on photoallergic reactions induced by the topical contact of the skin with a chemical in the presence of, or followed by, exposure to UV or visible light. Some of the more recently observed photo-allergens and those presenting special clinical features are discussed. RESULTS: The literature cites several topical substances that give rise to photoallergic contact dermatitis, some of them only exceptionally but others quite frequently. The clinical features are not always those of a eczematous eruption, and several parts of the body may be affected. CONCLUSIONS: Many topical photoallergic culprits have been reported in the literature, the most important of which are sunscreen agents and, recently, non-steroidal anti-inflammatory agents (NSAIDs). Not at all exceptional is the occurrence of photoaggravation and recurrent transient or even persistent light reactions on previously exposed as well as non-exposed areas (often sparing the original application site), particularly with the NSAID ketoprofen. Moreover, cross-reactions with chemically-related as well as non-chemically related molecules are common. The potentially misleading clinical features observed in some cases, the diversity of the casual substances identified, and the low frequency with which photopatch testing is carried out in general indicate that the occurrence of photoallergic contact dermatitis might well be underestimated.