Warts are actually benign tumors of the epidermis caused by a virus. The virus responsible is the human papillomavirus (HPV), a double-stranded DNA virus. The virus resides in the bottom layer of the epidermis and replicates into almost normal-looking skin. Different sub-types of HPV cause different types of warts. Some human papilloma-virus subtypes also cause cervical cancer and other more obscure types of wart-related cancers.
