Computer artwork of a human papilloma virus (HPV). The protein coats, or capsids enclose their genetic material. The capsids are studded with surface proteins. HPV causes warts, which commonly grow on the hands, the soles of the feet, the body's mucous membranes and the genitals. It has also been linked with some skin and cervical cancers. The papilloma virus belongs to the papovavirus group, most of whose members are capable of inducing non- malignant tumours.