Not life-threatening, warts are nevertheless annoying, disfiguring and potentially carcinogenic - and on the increase, particularly in patients with AIDS.

What are warts?
Warts are believed to be caused by the highly contagious human papillomavirus (HPV). It is usually acquired by direct contact with someone with warts, or through touching infected surfaces.

Common warts are hard, small, sharply defined rough growths on the skin. Despite their firmly anchored appearance, they only affect the topmost layers of skin. Warts often occur in clusters - mainly on the hands, but also on the face, forearms and feet.

Plantar warts, or verrucas, are also found on the feet, typically acquired in communal showers or locker-rooms.

These two types of warts can only take hold on punctured skin, which is why they often affect children, whose rough-and-tumble world exposes them to cuts and scrapes.

About 50 per cent of these warts disappear by themselves within six to 12 months.

Genital warts on the vagina, penis or anus are often larger than other warts and resemble a cauliflower. Transmitted exclusively by sexual contact, they may take as long as 18 months to appear after infection. Painless, but highly infectious, these are now commonly seen in AIDS patients, mainly because of the impaired immune system.

What doctors tell you
The usual treatment for warts is salicylic acid, from the willow tree. This powerful acid chemically burns away tissue (and so is also used for skin conditions like acne). Although milder than most treatments, it can still cause skin irritation, so should only be applied to the wart itself, after protecting the surrounding skin by, for example, Vaseline. Because of the skin irritation, diabetics need to take particular care when using it. Salicylic acid is available without a prescription.

Other drugs on offer range from tretinoin and corticosteroids to toxic anticancer drugs, such as fluorouracil (5-FU) and bleomycin.

More common is the removal of warts with a scalpel, or with more sophisticated techniques, such as electrocauterisation, laser and cryosurgery. The last uses liquid nitrogen to freeze the wart to detach it from the skin.

Nevertheless, warts remain 'a therapeutic challenge', mainly because they often recur, even after the most aggressive treatments (Adolesc Med, 2001; 12: vi, 229-42).

In a recent review of the data for conventional treatments, there was either little evidence of success, or none was any better than salicylic acid (75 per cent effective) or duct tape (see box; Cochrane Database Syst Rev, 2003; 3: CD001781).

As for genital warts, for which standard (mainly surgical) treatments are 'highly unsatisfactory' (Eur J Dermatol, 1998; 8 [7 Suppl]: 4), the relatively new drug imiquimod has been hailed as a breakthrough - yet, it is only effective in about one in three cases (J Eur Acad Dermatol Venereol, 2004; 18: 314-7). It also produces a raft of side-effects, including redness, itching, burning or flaking of the skin, localised blisters, scabs, swelling and pain, muscle weakness, fever, flu-like symptoms and fungal infection.

Tony Edwards