The Frequency and Causes of Photoallergic Contact Dermatitis among Dermatology Outpatients

Too many patients with photoallergy remain undiagnosed due to unsatisfactory knowledge among doctors and limited access to photopatch testing. The objectives of this study were to analyze the frequency of patients requiring diagnostic work-up for photoallergic contact dermatitis among dermatology patients, and to identify the causative photosensitizers. This prospective study involved 1000 consecutive, first-referred dermatology outpatients. All patients with a history of dermatitis induced or aggravated by exposure to light were qualified for photopatch testing. In the study group, 36 (3.6%; 95%CI: 2.4-4.8%) persons required photopatch testing based on their clinical symptoms. As the total number of patients requiring patch tests of any kind amounted to 205, the percentage of photopatch tested patients among all patch-tested patients was 17.5% (95%CI: 12.2-22.8%). Photoallergic contact dermatitis was ultimately confirmed in 15 (1.5%; 0.7-2.3%) persons: 7 females and 8 males aged 6-60 (median 33) years. Nine patients turned out photoallergic to at least one nonsteroidal anti-inflammatory drug, with ketoprofen photoallergy being most frequent (5 patients, in each case clinically relevant), followed by etofenamate (4 non-relevant reactions) and diclofenac (1 relevant reaction). Five patients were positive to at least one organic sunscreen, most frequently to benzophenone-3 (2 patients). "Classical" contact allergy to tested photohaptens was found in 15 persons, including 7 with coexisting photoallergy. In conclusion, patients requiring diagnostic work-up for photoallergy constitute a relevant group among dermatology patients, therefore, it seems advisable that all second-level dermatology referral centers be capable of photopatch testing. Due attention should also be paid to photoallergy in dermatology training.