Benzoyl peroxide (pronounced /ˈbɛnzɔɪl pəˈrɒksaɪd/) is a chemical in the organic peroxide family. It consists of two benzoyl groups (benzaldehyde with the H of CHO removed) joined by a peroxide group.

Uses

Benzoyl peroxide is a radical initiator. Homolytic cleavage of the weak oxygen-oxygen bond forms free radicals which trigger further reactions.

Jack Breitbart of Revlon laboratories first developed Benzoyl peroxide's use for treating acne in the 1920s.^[1] It is typically placed over the affected areas in gel or cream form, in concentrations of 2.5% increasing through the usually effective 5% to up to 10%. Research suggests that 5 and 10% concentrations are not significantly more effective than 2.5% and 2.5% is usually better tolerated.^[2][3] It commonly causes initial dryness and sometimes irritation, although skin tolerance usually occurs after a week or so. A small percentage of people are much more sensitive to it and liable to suffer burning, itching, peeling and possibly swelling^[4]. It is sensible to apply the lowest concentration and build up as appropriate. Once tolerance is achieved, increasing the quantity or concentration a second time and gaining tolerance at a higher level usually gives better subsequent acne clearance. Benzoyl peroxide works as a peeling agent, increasing skin turnover and clearing pores, thus reducing the bacterial count there as well as directly as an antibacterial.

Other common uses for benzoyl peroxide include dyeing hair, and as an active ingredient in teeth whitening systems. It is also used in the preparation of flour, and can be used as an initiator and catalyst for polyester thermoset resins (as an alternative to the much more hazardous methyl ethyl ketone peroxide).

Adverse effects

In a 1977 study using a human maximization test, 76% of subjects acquired a contact sensitation to benzoyl peroxide. Formulations of 5% and 10% were used.^[5]

Safety

Pure benzoyl peroxide is highly flammable, explosive, toxic and a possible tumor promoter and may act as a mutagen^[6], and should be handled with care.

Diluted in an ointment, benzoyl peroxide is used as an acne treatment and the following precautions and claims pertain to this use. Attention should be paid to the safety directions provided when purchased.

In the United States, the typical concentration for benzoyl peroxide is 2.5% to 10% for both prescription and over the counter use. Benzoyl peroxide, like most peroxides, is a powerful bleaching agent. Contact with fabric (including clothing and bed linens) or hair can cause permanent color dampening almost immediately.

Benzoyl peroxide breaks down in contact with skin, producing benzoic acid and oxygen, neither of which are significantly toxic.^[7]

When applied to skin benzoyl peroxide has been shown to induce cancer, but only when used at 100% concentrations; it has not been shown to do this at the far lower concentrations used for treating acne, and at lower concentrations benzoyl peroxide has not been found to be mutagenic or carcinogenic.^{[citation needed]}

Benzoyl peroxide removes the top layer of skin, which also decreases the sun protective effect (roughly SPF 3). This can cause sunburn and premature aging if sun protection is not worn. If sun protection is used, benzoyl peroxide has effects similar to glycolic acid peels which are so-called anti-aging treatments.

Double Displacement

Mixing sodium peroxide with benzoyl chloride gives benzoyl peroxide and sodium chloride.

Decomposition

The half-life of benzoyl peroxide is one hour at 92°C. At 131°C, the half-life is one minute. ^[8]

References