Dr. Greene, my 10 year old has suddenly gotten warts on her feet. What could be the cause when none of the other members of the family have them? What can I do to treat them so they won't come back?

Under a magnifying glass the roughened surface of a wart often looks like a tiny cauliflower. The little black dots sometimes seen are the ends of blood vessels that the wart has recruited to bring it food. Contrary to well-established belief, the underside of a wart is smooth and round, and the entire wart is confined to the epidermis -- the outermost layer of the skin. There are no 'roots'!

Even without roots, warts can be difficult to destroy.

Warts are infections caused by viruses that are present everywhere, making them among the most common of all childhood skin conditions. The culprit will be one of more than 70 types of human papillomaviruses (HPV). They are contagious, and they are spread when the virus touches a part of the skin where the outer protective layer is broken, either by minor trauma or by moisture. This happens most commonly on the fingers, elbows, knees, and the bottoms of the feet. Warts on the bottom of the feet are called plantar warts - named for the plantar surface (sole) of the foot.

Some people get warts more easily than other people. Warts are more common in children than in adults, partly because of their less mature immune systems and partly because they spend more time in wet-floored locker rooms and in active, close play. Wearing something on the feet in locker rooms and at the pool can prevent many plantar warts.

Most warts will eventually go away on their own, expelled by the body's immune system. About 25% are gone within 3-6 months and 65% disappear within 2 years. Unfortunately, some warts may persist for years. Warts will not leaves scars, though some of the more aggressive wart therapies might.

Plantar warts often make running, jumping, and even walking, uncomfortable. The tenderness can change posture and cause strain elsewhere in the body. A little wart can be a big problem. Sometimes filing with an emory board and/or wearing a doughnut bandage can alleviate the discomfort. The warts are usually most tender when they are growing most rapidly. Often, the pain will disappear within a few days even if nothing is done. Warts should be treated if they are spreading, unsightly, or continue to be painful.

Treatments abound, varying from as gentle and simple as taping a patch of banana peel on before bed, to as high-tech and powerful as superpulsed carbon-dioxide-laser vaporization.

The active ingredient in most over-the-counter remedies is salicylic acid, a natural substance found in many plants (willow bark) and most fruits. It can be applied either as a liquid or a patch (I prefer the patch). With regular application, many warts will disappear within 12 weeks. These topical treatments often work best if the surface of the wart is disrupted with warm soaks and/or an emory board before application.

If you are not certain that your child has a wart, you may want to have your child’s doctor examine his or her skin before trying an over-the-counter treatment, since some other skin conditions can look similar but need different treatments.

Physicians use many options to treat warts (surgery, lasers, chemical cautery, electrodesiccation, lasers, and even chemotherapy) but freezing is the most common, especially for smaller warts.