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Skeletal formula (top) Ball-and-stick model (bottom)
Treatment with benzoyl peroxide was proposed for wounds by Lyon and Reynolds in 1929, and for sycosis vulgaris and acne varioliformis by Peck and Chagrin in 1934. However, preparations were often of questionable quality. It was officially approved for the treatment of acne in the US in 1960.
Tube of a water-based 5% benzoyl peroxide preparation for the treatment of acne
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.
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.
Skin irritation due to benzoyl peroxide
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.
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.
Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which is very toxic.
The carcinogenic potential of benzoyl peroxide has been investigated. 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. The study concluded, "caution should be recommended in the use of this and other free radical-generating compounds".
A 1999 IARC review of carcinogenicity studies found no convincing evidence linking BPO acne medication to skin cancers in humans. However, some animal studied found that the compound could act as a carcinogen and enhance the effect of known carcinogens.
In a 1977 study using a human maximization test, 76% of subjects acquired a contact sensitization to benzoyl peroxide. Formulations of 5% and 10% were used.
A bleached fabric stain caused by contact with benzoyl peroxide.
Contact with fabrics or hair, such as from still-moist acne medication, can cause permanent color dampening almost immediately. Even secondary contact can cause bleaching; for example, contact with a towel that has been used to wash off benzoyl peroxide-containing hygiene products.
The oxygen-oxygen bond in peroxides is weak. Thus, benzoyl peroxide readily undergoes homolysis (symmetrical fission), forming free radicals:
(C6H5CO)2O2 -> 2
The symbol o indicates that the products are radicals; i.e., they contain at least one unpaired electron. Such species are highly reactive. The homolysis is usually induced by heating. The half-life of benzoyl peroxide is one hour at 92 °C. At 131 °C, the half-life is one minute.
^World Health Organization (2019). World Health Organization model list of essential medicines: 21st list 2019. Geneva: World Health Organization. hdl:10665/325771. WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO.
^ abHamilton R (2015). Tarascon Pocket Pharmacopoeia 2015 Deluxe Lab-Coat Edition. Jones & Bartlett Learning. p. 173. ISBN9781284057560.
^ abSeidler EM, Kimball AB (July 2010). "Meta-analysis comparing efficacy of benzoyl peroxide, clindamycin, benzoyl peroxide with salicylic acid, and combination benzoyl peroxide/clindamycin in acne". Journal of the American Academy of Dermatology. 63 (1): 52-62. doi:10.1016/j.jaad.2009.07.052. PMID20488582.
^Jeanmougin M, Pedreiro J, Bouchet J, Civatte J (1983-01-01). "[Phototoxic activity of 5% benzoyl peroxide in man. Use of a new methodology]". Dermatologica. 167 (1): 19-23. doi:10.1159/000249739. PMID6628794.
^Li III H (1998). "Chapter 2"(PDF). Synthesis, Characterization and Properties of Vinyl Ester Matrix Resins (Ph.D.). University of Vermont. hdl:10919/30521. Archived from the original on 2006-09-20. Retrieved .