Warts are non-cancerous skin growths that occur when a virus infects the top layer of the skin. There are multiple types of warts including common warts (verruca vulgaris), plantar warts, flat warts, and filiform warts. Warts are typically skin-colored and rough, but they may also appear dark (brown or gray-black), flat, and smooth. The appearance of the wart depends on where it is growing. Wart viruses are contagious. Warts can spread from contact with a wart or with something that touched a wart. In children, warts can disappear without treatment over a period of several months to years. However, warts that are bothersome, painful, or rapidly multiplying should be treated. Warts in adults often do not disappear as easily or quickly as they do in children.