Warts are often skin-colored and feel rough, but they can be dark (brown or gray-black), flat, and smooth. Warts are benign (non-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.