Fixed combination therapy in acne is standard of care, and benzoyl peroxide is a common component of a number of fixed-dose combination products available today. Given that benzoyl peroxide can cause concentration-dependent irritation, newer combinations have been developed utilizing lower concentrations (2.5%) in their formulation. These formulations have been shown to provide better tolerability than products with higher benzoyl peroxide concentrations, while offering comparable efficacy. In vitro skin permeation studies can be used to determine the relative availability of benzoyl peroxide from different dosage forms. In this in vitro percutaneous absorption study, the authors compared three fixed combinations, two with 2.5% benzoyl peroxide and one with 5% benzoyl peroxide. Both 2.5% benzoyl peroxide products (1.2% clindamycin phosphate and 2.5% benzoyl peroxide, and 0.1% adapalene and 2.5% benzoyl peroxide) had similar benzoyl peroxide delivery profiles in terms of efficiency of deposition and total benzoyl peroxide tissue permeation. Although 1.2% clindamycin phosphate and 2.5% benzoyl peroxide delivered the same amount of benzoyl peroxide into the receptor fluid as 1.2% clindamycin phosphate and 5% benzoyl peroxide, it was statistically more efficient in terms of percent applied dose (P=0.002). This suggests a more advanced formulation, as it contains only half the concentration of benzoyl peroxide. All three products showed similar delivery characteristics in terms of the amount of benzoyl peroxide depositing into the dermis.