Photoallergic contact dermatitis is uncommon

Background Despite the enormous increase in sunscreen use, allergic contact (AC) and photoallergic (PA) reactions to ultraviolet (UV) filters are cons idered rare. Objectives To analyse the data from 2715 patients who underwen t photopatch testing at St John's Institute of Dermatology during the perio d 1983-98. Methods A retrospective analysis of all positive photopatch test episodes w as undertaken with the results retrieved from the environmental dermatology database and further verified with the original archived patch test docume ntation for each individual patient. Results In 111 patients with positive reactions (4.1%), there were 155 AC o r PA reactions to allergens in the photopatch test series. Eighty PA reacti ons were observed in 62 (2.3%) patients (32 men and 30 women, age range 28- 75 years), with UV filters accounting for 52 positive reactions (65%). drug s 16 (20%), musk ambrette 11 (14%) and the antiseptic trichlorocarbanilide one (1%). The most common UV filter photoallergen was benzophenone-3 with 1 4 positive results, followed by benzophenone-10 (n = 9), isopropyl dibenzoy lmethane (n = 6), p-aminobenzoic acid (PABA) (n = 5), octyl dimethyl PABA ( n = 5), butyl methoxydibenzoylmethane (n = 4), isoamyl methoxycinnamate (n = 2), ethyl methoxycinnamate (n = 2), octyl methoxycinnamate (n = 2). amyl dimethyl PABA (n = 2) and phenylbenzimidazole sulphonic acid (n = 1). A sim ilar number of AC reactions to UV filters was detected in this study. Thus 49 patients (1.8%) had a total of 75 reactions: 51 due to UV filters and 24 as a result of exposure to fragrances and therapeutic agents. Benzophenone -10 accounted for 13 AC reactions and benzophenone-3 for eight reactions. T wenty-two patients had a PA reaction alone, whereas 19 patients had chronic actinic dermatitis and 15 patients polymorphic light eruption (PLE) in add ition. Thus, 34 of the 62 patients (55%) had a preceding underlying photode rmatosis. Conclusions These results show a low yield of positive photopatch tests. Th us, despite the large increase in the use of UV filters over the last decad e, the development of PA reactions remains rare. Furthermore, most of the c ommon UV filter photoallergens identified in this study, including PABA, am yl dimethyl PABA and benzophenone-10. are now rarely used in sunscreen manu facture, while isopropyl dibenzoylmethane was voluntarily removed from the market in 1993. Currently, benzophenone-3 is the commonest contact photoall ergen still in widespread use. In contrast, the UVB filter octyl methoxycin namate, used in a number of sunscreens, produced only two positive PA react ions in 12 years of testing. Nevertheless, although these reactions are ext remely rare, patients with photodermatoses such as PIE and chronic actinic dermatitis do represent a group of patients at increased risk of developing photoallergy. Further photopatch test series should be regularly reviewed and updated, as the relevance of individual photoallergens changes over tim e. Currently, there is no evidence that PA reactions represent a common cli nical problem.