Human papilloma virus (HPV). Computer illustration showing the structure of the protein coat (capsid) surrounding a human papilloma virus (HPV) particle (virion). The capsid is made up of pentameters of the protein L1 and encloses DNA (deoxyribonucleic acid), the genetic material of the virus. HPV causes warts, which mostly occur on the hands and feet. Certain strains also infect the genitals. Although most warts are non-malignant (not cancerous), some strains of HPV have been associated with cancers, especially cervical cancer.