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).
Wart viruses are contagious. Warts can spread by contact with the wart or something that touched the wart. Warts are often skin-colored and feel rough, but they can be dark (brown or gray-black), flat, and smooth.