Photo © GMFA
The human papilloma virus (HPV), of which there are over a hundred strains can, in some people cause either warts or pre-cancer (strains 16 and 18 are the worst).
Most sexually active people have, at some point evidence of HPV in their system, though are unaffected. In a very small proportion of people it causes problems (anal, cervical, penile, or throat pre-cancer/cancer). Living with HIV has been shown to increase the risk of acquiring anal pre-cancer for men who have unpr