Sometimes even Dr Google is wrong: An unusual contact dermatitis caused by benzoyl peroxide

A 32-year-old non-atopic male presented with intense pruritic erythematous dermatitis in his groins and scrotum (Figure 1A) after selfadministration of various unspecified topical medicaments. The patient reported that he had searched for his symptoms, namely “burning and redness”, on Google, and had come to the conclusion he was suffering from an infection. He therefore applied Benzac 5% gel, as suggested online, but the skin eruption worsened. Thereafter, he used PREP cream, which, according to online descriptions, had “calming properties”, but there was no improvement. Finally, our treatment with systemic antihistaminic and topical corticosteroids and antibiotics along with cessation of other topical medicaments led to rapid resolution of the dermatitis. Patch testing was performed with the Italian Society of Allergological, Occupational and Environmental Dermatology (SIDAPA) baseline series (Lofarma, Milano, Italy) on Van der Bend chambers (Van der Bend, Brielle, The Netherlands) and with both of the abovementioned topical products tested “as is”. Patch tests were applied under occlusion on the patient’s back for 2 days; readings were performed on day (D) 2 and D4 according to ESCD guidelines. A positive reaction (++ on D4) was observed to the patient’s own product, Benzac gel 5% (Figure 1B). Further patch testing with benzoyl peroxide 2% pet. was performed, and yielded an extreme positive reaction (+++) on D4 (Figure 1C). Allergic contact dermatitis caused by benzoyl peroxide was thus diagnosed.