Warts are caused by an infection with the human papilloma virus (HPV) . The virus enters the skin through a cut or break and causes an infection that forms warts. There are more than 100 different strains of HPV, and different strains are responsible for different types of warts. Warts are contagious and can be transmitted by touch or indirectly from contaminated objects or surfaces. The virus usually spreads through breaks in the skin, such as a hangnail or a scrape. Warts are non-cancerous and usually harmless, but they can be bothersome or embarrassing.