Patch testing with benzoyl peroxide: reaction profile and interpretation of positive patch test reactions

Background: Patch testing with benzoyl peroxide 1% pet. frequently leads to (weak) positive reactions, often with uncertain clinical relevance.
Objectives: To describe the pattern of patch tests reactions to benzoyl peroxide and to identify patients at risk of a positive reaction.
Methods: Retrospective analysis of data from the Information Network of Departments of Dermatology (IVDK), 1992–2007.
Results: Benzoyl peroxide 1% pet. was tested in 29 758 patients. Weak positive reactions (erythema, infiltration, possibly papules) occurred in 6.5%, and strong positive reactions (erythema, infiltration, vesicles) in 1.3%. According to logistic regression analysis, strong positive reactions to benzoyl peroxide were associated with leg or face dermatitis, work as dental technicians, young age and being female. Patients with atopic dermatitis had a significantly increased risk of weak positive reactions only.
Conclusions: Our analysis confirms that benzoyl peroxide 1% pet. is a problematic patch test preparation. Hence, clinical relevance of reactions to benzoyl peroxide has to be assessed very carefully. Patients with atopic dermatitis are particularly prone to irritant reactions to benzoyl peroxide. True allergic reactions may occur in dental technicians and following the treatment of leg ulcers with highly concentrated benzoyl peroxide in past. In contrast, widely used acne treatments with benzoyl peroxide seems to sensitize only rarely.