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Acne is a disorder of the pilosebaceous follicle; common features include increased sebum production, follicular keratinisation, colonisation by Propionibacterium acnes, and localised inflammation. Mild acne is characterised by open or closed comedones (blackheads and whiteheads), some of the latter developing into inflamed lesions such as papules and pustules. In moderate acne, the papules and pustules are more widespread, and there may be mild scarring. Severe acne is characterised by the presence of nodular abscesses or cysts in addition to widespread pustules and papules, and may lead to extensive scarring.

The most common form of acne is acne vulgaris. It is common in teenagers and while by their mid-20s the majority of cases have resolved, a few people still require treatment in their 30s and 40s. Skin areas typically affected are the face, shoulders, upper chest, and back. Acne may also occur in late middle age and in the elderly (late onset acne) and in infants (infantile acne).

Certain drugs, including androgens, corticosteroids, corticotropin, hormonal contraceptives containing androgenic progestogens such as levonorgestrel, isoniazid, lithium, methoxsalen, and some antiepileptics may produce an acneform rash, as may substances such as tars, oils, and oily cosmetics.

Treatment aims to reduce the bacterial population of the pilosebaceous follicles, reduce the rate of sebum production, reduce inflammation, and remove the keratinised layer blocking the follicles. Drugs used include keratolytics, retinoids, and antibacterials. If topical preparations are not effective, oral preparations may be required. Response to therapy is commonly slow and long-term treatment is usually necessary.1-7

Mild acne is treated topically, in particular with benzoyl peroxide, retinoids, or antibacterials. Abrasives have been used but their effectiveness is doubtful, and preparations based on sulfur or salicylic acid are considered by some to be obsolete; the effectiveness of degreasing agents has also been questioned. Topical corticosteroids, despite their presence in some compound preparations, should not be used.

Benzoyl peroxide has an antimicrobial action and mild keratolytic properties, and both comedones and inflammation generally respond well. It is probably the most widely used first-line drug. Azelaic acid is an alternative to benzoyl peroxide that may cause less local irritation. Both have been used with other topical agents.

Topical retinoids are an alternative to benzoyl peroxide and some dermatologists consider them to be the treatment of choice for mild to moderate comedonal acne. Isotretinoin and tretinoin appear to be equally effective when used topically; tazarotene is a recently-introduced retinoid for topical use and adapalene, a naphthoic acid derivative, may also be used. Topical retinoids and antibacterials may be particularly effective if used together, since antibacterials are more effective for inflammation and retinoids for comedones; retinoids may also be alternated with benzoyl peroxide.

Topical antibacterials may be used particularly for inflammatory acne, if benzoyl peroxide application is ineffective or poorly tolerated. Tetracycline, clindamycin, and erythromycin are generally available as solutions for topical use, and appear to be roughly equivalent in efficacy. However, development of resistance by the skin flora is an increasing problem.

Combination therapy with benzoyl peroxide and erythromycin may help to prevent the selection of resistant mutants; alternatively, short intervening courses of benzoyl peroxide or azelaic acid during antibacterial therapy may help to eliminate any resistant bacteria that have been selected. Response to treatment should be assessed after 6 to 8 weeks. It has also been recommended:8

that courses of topical antibacterials be continued for no longer than necessary (although treatment should be used for at least 6 months)
that the same drug be used if further treatment is required
that use of different oral and topical antibacterials at the same time, or rotation of antibacterials, be avoided.

Nicotinamide is also used topically in mild to moderate acne.

Moderate acne is best treated with oral antibacterials. Topical drugs may also be used as adjunctive anticomedonal treatment. Of the oral antibacterials tetracyclines appear to be the drugs of first choice. Tetracycline, doxycycline, lymecycline, or oxytetracycline may be used. Minocycline has also been reported to be effective; however, it can cause skin pigmentation and may be associated rarely with immunologically mediated reactions.

Alternatives to the tetracyclines include erythromycin, co-trimoxazole, and trimethoprim. All oral antibacterials have to be used for at least 3 months; the maximal response is thought to occur after 3 to 6 months, although in some cases treatment for 2 or more years may be necessary. Again, resistance may be a problem particularly with erythromycin.

Women with moderate acne who also require oral contraception may be treated additionally with a combined oral contraceptive containing a non-androgenic progestogen.

Severe acne is usually treated with oral isotretinoin. Where it cannot be used, high doses of oral antibacterials may be considered. In women with hormonal disturbances, the anti-androgen cyproterone with ethinylestradiol (available as a combination preparation) or a combined (non-androgenic) contraceptive may be effective as adjunctive treatment. Spironolactone (used for its anti-androgenic properties) has been advocated for women in whom oestrogens are contra-indicated. Colchicine is being investigated in acne resistant to antibacterial treatment.

Topical drugs, particularly antibacterials, described above under mild acne, may be used as adjunctive treatment.

There is evidence to suggest that photodynamic therapy with a photosensitiser, such as 5-aminolevulinic acid, may be beneficial in acne.

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