Benzoyl peroxide has been used to treat acne for more than 60 years and is generally accepted as the most effective topical treatment for mild conditions.

How does it act?

Two main mechanisms of action have been proposed:

• A comedolytic effect through an irritant action, leading to increased turnover of the epithelial cells lining the follicular duct and increasing sloughing
• As a bactericide against P acnes.

Benzoyl peroxide is lipophilic and therefore penetrates the follicle well. Once absorbed, it releases oxygen, which suppresses the bacteria, thereby reducing the production of irritant-free fatty acids.

Adverse effects, cautions and use

Benzoyl peroxide is mildly irritant and may cause redness, stinging and peeling, especially at the start of treatment, but tolerance usually develops with continued use. To minimise these effects, the lower strength (5 per cent) should be used at night for the first week so that any erythema subsides by the following morning.

If there is no adverse reaction, application can be increased to twice daily. Several weeks of regular application are usually required to produce real benefit. If the lower strength is ineffective, the higher strength (10 per cent) can be tried. Treatment should not be prolonged beyond three months with the 5 per cent preparations or beyond two months with the 10 per cent preparations.

True allergy occurs in a small minority of patients, but allergic contact dermatitis is more common. If troublesome skin irritation occurs, application should be stopped for a day or two, and discontinued if the reaction recurs. Benzoyl peroxide is an oxidising agent and may bleach clothing and bed linen.