A wart, or verruca, is a small growth on the surface of the skin caused by the human papillomavirus (HPV). A wart can be smooth and have a flat top, or it can be raised. Several kinds ofwarts exist, including plantar warts, which appear only on the soles of the feet, and filiform warts, which have a fingerlike shape and tend to appear near the eyes, nose, or mouth.

HPV is contagious. It can be contracted directly (by touching a wart) or indirectly (by touching something that came in contact with a person with a wart, such as a locker room floor). Kids sometimes contract warts after getting a cut on the hand or foot or after tearing a hangnail. The HPV virus enters easily through such wounds.

Not all people get warts, however. Scientists think that the immune system of certain people protects them against HPV.

Warts can be difficult to remove. Popular treatments include over-the-counter solutions, which are brushed onto the wart; laser surgery; and cryosurgery, a procedure in which super-cold liquid nitrogen is applied to the wart.