HPV is short for human papillomavirus, a very common virus that infects nearly everyone at some point.
There are many different strains of the virus, each identified with a number. HPV 16 and 18 are high-risk types known to significantly increase the risk of cervical, vaginal, and vulvar cancer in women, as well as penile cancer in men. The strains can also cause anal cancer and throat cancers in men and women.
About 40 of the 150 or so types of HPV can infect the genital regions and other mucous membranes (such as the mouth and throat), but only a portion of these can cause cancer.
In most people, HPV infections are transient, since the infected cells are shed from the body naturally. In a minority of people, though, the HPV persists, and if the persistent HPV is type 16 or 18, there is a marked increase in the risk of developing genital, anal, or oral cancer (depending on where the infection is located).
But even in people whose HPV persists, the time from infection with a high-risk HPV type to the development of cancer is generally measured in years.
For women, such slow growth allows precancerous changes in the cervical cells, called dysplasia, to be found on screening Pap tests or, more recently, HPV tests that look for high-risk types of HPV in the cells of the cervix.