No strong evidence supports the idea that higher concentrations of benzoyl peroxide are more effective than lower concentrations. 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. Side effects
Application of benzoyl peroxide to the skin may result in redness, burning, and irritation. This side effect is dose-dependent.Because of these possible side effects, it is recommended to start with a low concentration and build up as appropriate, as the skin gradually develops tolerance to the medication. Skin sensitivity typically resolves after a few weeks of continuous use.
Irritation can also be reduced by avoiding harsh facial cleansers and wearing sunscreen prior to sun exposure.One in 500 people experience hypersensitivity to BPO and are liable to experience burning, itching, crusting, and possibly swelling. About one-third of people experience phototoxicity under exposure to ultraviolet (UVB) light. Dosage
In the U.S., the typical concentration for benzoyl peroxide is 2.5% to 10% for both prescription and over-the-counter drug preparations that are used in treatment for acne. Other medical uses
Benzoyl peroxide is used in dentistry as a tooth whitening product. Non-medical uses
Bleaching
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. Polymerization
Benzoyl peroxide is also used as a radical initiator to induce chain-growth polymerization reactions, such as for polyester and poly(methyl methacrylate) (PMMA) resins and dental cements and restoratives. It is the most important among the various organic peroxides used for this purpose, a relatively safe alternative to the much more hazardous methyl ethyl ketone peroxide. It is also used in rubber curing and as a finishing agent for some acetate yarns. Safety
Explosion hazard
Concentrated benzoyl peroxide is potentially explosive like other organic peroxides, and can cause fires without external ignition. The hazard is acute for the pure material, so the compound is generally used as a solution or a paste. For example, cosmetics contain only a small percentage of benzoyl peroxide and pose no explosion risk.