Warts are caused by a virus called the human papillomavirus (HPV). Multiple strains exist, are contagious and cause small or large, smooth or rough growths, that can appear anywhere on the skin surface. Some warts may respond to one treatment such as small facial flat warts whereas thicker warts on the palms and soles may require multiple treatments. Treatment options include liquid nitrogen, cantharidin, injections of candida antigen, 5-fluorouracil or bleomycin.