[16] Donald Holroyde Hey FRS[17] (12 September 1904 – 21 January 1987) was a Welsh organic chemist who inferred that the decomposition of benzoyl peroxide generated free phenyl radicals.

[22] Around 1905, Loevenhart reported on the successful use of benzoyl peroxide to treat various skin conditions, including burns, chronic varicose leg tumors, and tinea sycosis.

[7] Benzoyl peroxide is mainly used as a radical initiator to induce chain-growth polymerization reactions,[5] such as for polyester and poly(methyl methacrylate) (PMMA) resins and dental cements and restoratives.

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%.

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,[7] and it was thought to decrease sebum production, but disagreement exists within the literature on this.

In micromolar concentrations it prevents neutrophils from releasing reactive oxygen species, part of the inflammatory response in acne.

[9][13] 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.

[32][33] Irritation can also be reduced by avoiding harsh facial cleansers and wearing sunscreen prior to sun exposure.

[36] In the US, 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.

Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which is very toxic.

A 1981 study published in the journal Science found that although benzoyl peroxide is not a carcinogen, it does promote cell growth when applied to an initiated tumor.

[41] A 1999 IARC review of carcinogenicity studies found no convincing evidence linking benzoyl peroxide acne medication to skin cancers in humans.

[42][43] In a 1977, study using a human maximization test, 76% of subjects acquired a contact sensitization to benzoyl peroxide.