Prospective multicentre photopatch test study of photoallergy to sunscreens and nonsteroidal anti-inflammatory drugs in Europe

BACKGROUND: Whilst photopatch testing is recognized as the investigation of choice for photoallergic contact dermatitis, changes in potential photoallergen exposure and variables within the photopatch test technique, have led to challenges in its usage within dermatology. OBJECTIVES: The main objectives of this study were to determine the nature and prevalence of topical photoallergens in Europe and investigate the variable of photoallergen occlusion time before irradiation, on photopatch testing outcomes. METHODS: A prospective multi-centre study of photopatch testing to sunscreens, non-steroidal anti-inflammatory drugs (NSAIDs) and other agents was conducted in 10 centres across seven European countries. A within-subject comparison of a 24h and 48h occlusion period prior to irradiation was included in the study design, to investigate the effect of this variable on photopatch testing outcomes. RESULTS: Of study participants, 28 photoallergic reactions were seen, with 10% (13/132) of participants reacting to sunscreen chemicals and 9% (9/101) to NSAIDs. The most prevalent photoallergens were ketoprofen (n=6), promethazine (n=4); butylmethoxydibenzoylmethane (Avobenzone/Parsol 1789) (n=4), benzophenone-3 (oxybenzone) (n=3) and etofenamate (n=3). Contact allergies were less frequent (14 reactions). When a 24h occlusion was used prior to irradiation, 53% of sunscreen photoallergic reactions and 36% of NSAID reactions were missed compared with the 48h occlusion. Most participants had a history of photo-exposed site dermatitis or sunscreen/NSAID reaction or had a photosensitivity disease, and 49% of participants had a history of dermatological conditions. All indications for photopatch testing were represented in those with positive photopatch tests, with no specific indicator of those most at risk. CONCLUSIONS: Photopatch testing remains an essential investigation for people with suspected photocontact allergies. Based on these study findings, the nature of topical photoallergens appears stable, but vigilance and ongoing review are required. To optimise the pick-up rate of photoallergy, we recommend, if practicable, a 48h occlusion period prior to irradiation.(Clinicaltrials.gov - NCT03812887).