Flexural skin eruption in a boy aged four months

A boy aged four months presented with an erythematous and desquamative eruption over intertriginous and flexural sites that had developed one month prior. Skin swabs taken by his general practitioner (GP) were negative for fungal infection. He had been treated with multiple courses of topical corticosteroids with no effect. A detailed history revealed only one relevant exposure: benzalkonium chloride (BAC) in a laundry rinse the family had been using in the general wash for the past six weeks. The patient had no significant medical history and did not take any regular medications. He had no known medication allergies, and his immunisation status was up to date. Physical examination revealed well-demarcated annular erythematous plaques associated with desquamation symmetrically distributed over the neck, chest, axillae and antecubital fossae (Figures 1 and 2).