is effective for treating acne lesions. It does not induce antibiotic resistance. It may be combined with salicylic acid, sulfur, erythromycin, or clindamycin (antibiotics), or adapalene (a synthetic retinoid). Two common combination drugs include benzoyl peroxide/clindamycin and adapalene/benzoyl peroxide, adapalene being a chemically stable retinoid that can be combined with benzoyl peroxide unlike Tazarotene and tretinoin. Combination products such as benzoyl peroxide/clindamycin and benzoyl peroxide/salicylic acid appear to be slightly more effective than benzoyl peroxide alone for the treatment of acne lesions. The combination tretinoin/benzoyl peroxide was approved for medical use in the United States in 2021. Benzoyl peroxide for acne treatment is typically applied to the affected areas in gel, cream, or liquid, in concentrations of 2.5% increasing through 5.0%, and up to 10%. No strong evidence supports the idea that higher concentrations of benzoyl peroxide are more effective than lower concentrations. Like most peroxides, it is a powerful bleaching agent. It has been used for the bleaching of flour, fats, oils, waxes, and cheeses, as well as a stain remover for ink stains on dolls. Mechanism of action Classically, benzoyl peroxide is thought to have a three-fold activity in treating acne. It is sebostatic, comedolytic, and inhibits growth of Cutibacterium acnes, the main bacterium associated with acne. In general, acne vulgaris is a hormone-mediated inflammation of sebaceous glands and hair follicles. Hormone changes cause an increase in keratin and sebum production, leading to blocked drainage. C. acnes has many lytic enzymes that break down the proteins and lipids in the sebum, leading to an inflammatory response. The free-radical reaction of benzoyl peroxide can break down the keratin, therefore unblocking the drainage of sebum (comedolytic). It can cause nonspecific peroxidation of C. acnes, making it bactericidal, and it was thought to decrease sebum production, but disagreement exists within the literature on this. Some evidence suggests that benzoyl peroxide has an anti-inflammatory effect as well. In micromolar concentrations it prevents neutrophils from releasing reactive oxygen species, part of the inflammatory response in acne. As a medication, benzoyl peroxide is mostly used to treat acne, either alone or in combination with other treatments. Some versions are sold mixed with antibiotics such as clindamycin. It is on the WHO List of Essential Medicines, and, in the US, it is available as an over-the-counter and generic medication. It is also used in dentistry for teeth whitening. Side effects Application of benzoyl peroxide to