Delayed type hypersensitivity to benzoyl peroxide.

Benzoyl peroxide (BP) has been a standard and effective topical treatment for acne vulgaris for the past 35 years. Previous studies and case reports have documented benzoyl peroxide to be a strong irritant and a weak allergen, with many cases of tolerance induced with repeat use of this irritant. While less common, numerous cases of BP-induced allergic contact dermatitis (delayed type hypersensitivity reaction) have been reported in the literature. We report here an individual with an incipient edematous reaction to topical BP used for acne therapy. This under-recognized presentation is discussed in the context of published literature on BP-induced hypersensitivity and irritation.