Photopatch testing in a tropical country, Thailand : 20 years' experience

Background: Photoallergic contact dermatitis is one of the important parts of photodermatoses. The investigation of choice is photopatch testing. However, reports with photopatch test results from Asian countries are scarce. The objective of this study was to determine the prevalence of positive photopatch test reactions and to ascertain the common photoallergens among Thai patients during 1998-2018. Methods: We retrospectively reviewed the records of 339 patients who were clinically suspected of having photoallergic contact dermatitis and had undergone photopatch testing. Results: A total of 44 photoallergic contact reactions in 38 patients (11.2%) were found. The positive photoallergic reactions were mainly found with organic ultraviolet filters and fragrances. Conclusions: Organic ultraviolet filter chemicals especially benzophenone-3 and fragrances were found to have a high prevalence of photoallergic contact reactions. Monitoring of the photoallergens employed in photopatch tests should be conducted periodically to provide the best patient care