Benzoyl peroxide is one of the most effective and safe topical agents for mild and moderately severe acne. Although it improves 50% to 75% of cases of akne, it exact mechanism of action is uncertain. When benzoyl peroxide is decomposed in the skin by cysteine, it liberates free oxygen radicals that oxidize bacterial proteins. This bactericidal action of benzoyl peroxide on acnes decreases the production of irritating fatty acids in sebum caused by this organism. The daily application of 10% benzoyl peroxide for two weeks can reduce free fatty acid concentrations in sebum by 50% and acnes levels by 98%. Benzoyl peroxide also is a primary irritant that increases the sloughing rate of epithelial cells and loosens the follicular plug structure, thereby exerting a "comedolytic" effect.

Benzoyl peroxide is available in lotions, washes, creams, and gels. These formulations are not equivalent in therapeutic potency of irritant potential. The gel formulations, for example, are more effective as well as more irritating that other benzoyl peroxide formulations and are available by prescription only.

Traditional nonprescription topical keratolytic agents such as sulfur, resoncinol, or salicylic acid appear to cause less irritation, but are generally considered less effective. Although combinations of these agents are frequently used for their supposed additive or "synergistic" effect, benefit from such products is often unproven.