Allergic contact angioedema to benzoyl peroxide.

Benzoyl peroxide (BP) is commonly used for topical acne treatment and has long been known to be a weak allergen and a strong irritant. We report a case of a 26-year-old woman, who presented with an itchy erythematous reaction and strong oedema localized to the face. Two weeks before angioedema, the patient had started a new topical treatment with a gel containing 10% BP for acne. She was patch tested to European Standard Series, including BP 1% in white petrolatum, and to the 10% BP-containing gel previously used by herself, showing positivity on day 2 to BP 1% and to the 10% BP-containing gel. Factors that suggested an association between the severe angioedematous reaction and BP topical application include the strong reaction to BP in the patch-test, the temporal relationship, the complete resolution of symptoms after the drug was withdrawn and the absence of other identified explanations.