ADVERSE REACTIONS Adverse reactions which may be encountered with topical benzoyl peroxide include excessive drying (manifested by marked peeling, erythema and possible edema), and allergic contact sensitization. Excessive dryness would appear to occur in approximately 2 patients in 50. Pertinent literature would seem to indicate that allergic sensitization to benzoyl peroxide may occur in 10 to 25 patients in 1,000. 7,8,9 There is one reference that reports an occurrence of sensitization in 5 of 100 patients. 10