A NEW prospective multi-centre European study has reinforced the importance of photopatch testing in diagnosing photoallergic contact dermatitis, while highlighting key methodological factors that may influence diagnostic accuracy.
The study analysed photopatch test results from 10 centres across seven European countries, focusing on reactions to sunscreens, non-steroidal anti-inflammatory drugs (NSAIDs), and other topical agents. Researchers also examined whether occlusion duration prior to irradiation affected outcomes, comparing 24-hour versus 48-hour application periods within the same patients.
Among participants, 28 photoallergic reactions were identified. Sunscreen agents triggered reactions in 10% of tested individuals (13/132), while NSAIDs accounted for 9% (9/101). The most frequently implicated photoallergens included ketoprofen, promethazine, butylmethoxydibenzoylmethane (avobenzone), benzophenone-3 (oxybenzone), and etofenamate. In contrast, classic contact allergies were less common, with only 14 reactions recorded.
48-Hour Occlusion Significantly Improves Detection Rates
A key finding of the study was the significant impact of occlusion duration on diagnostic sensitivity. Using a 24-hour occlusion period prior to irradiation resulted in a substantial proportion of missed cases, 53% of sunscreen-related photoallergies and 36% of NSAID-related reactions were not detected compared to the 48-hour protocol. These findings suggest that shorter occlusion times may underestimate the true prevalence of photoallergy.
No Clear Predictors of Photoallergy Risk Identified
Participants in the study often had a history of photosensitive dermatitis, suspected reactions to sunscreens or NSAIDs, or underlying photosensitivity disorders. Nearly half also reported pre-existing dermatological conditions. However, the study found no clear clinical predictors that could reliably identify individuals at higher risk of photoallergy, underscoring the broad applicability of photopatch testing.
Overall, the authors conclude that while the spectrum of topical photoallergens in Europe remains relatively stable, continued vigilance is required. Crucially, they recommend adopting a 48-hour occlusion period, where feasible, to optimise detection rates and improve diagnostic accuracy in clinical practice.
These findings may prompt a reassessment of current photopatch testing protocols, with implications for both dermatology research and patient care.
Reference
Ralph N et al. Prospective multi-centre photopatch test study of photoallergy to sunscreens and NSAIDs in Europe. Br J Dermatol. 2026:doi: 10.1093/bjd/ljag085
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