Warts are benign (not cancerous) skin growths that appear when a virus infects the top layer of the skin. Viruses that cause warts are called human papillomavirus (HPV). You are more likely to get one of these viruses if you cut or damage your skin in some way.

Wart viruses are contagious. Warts can spread by contact with the wart or something that touched the wart.

Types of warts:

Plantar warts: Warts on the bottom of the foot feel deep, but they are still within the superficial layer of the skin. Salicylic-acid drops and plasters help remove the thick overlying callus and make the wart feel less like a marble in your shoe. Nonprescription aerosol freezing may be used as well.

Common hand warts:These are typically unattractive, although not painful. Salicylic acid can make them smaller and go away in some cases, as can nonprescription freezing. If you have an all-but-impossible case, don’t try too hard. You don’t want to make the treatment worse than the disease.

Examples:

Warts under the nails: These are extremely resistant to treatment. One or two tries by the doctor are worth a shot, but if they fail, putting acid on them yourself just makes them look rough and unattractive.

“Mosaic” warts: Tiny, so-called “seed warts” can proliferate by the dozens or hundreds all over the sole of the foot. They don’t usually hurt, and they rarely respond to any sort of treatment, although in this case, too, one or two tries at treatment may be in order.

Flat warts: These are small, flat, flesh-colored pimples and may be numerous on one part of the body (for example on the face, arms, or groin). Getting rid of them by a light application of salicylic acid or other method is easy enough, but they have a tendency to recur.