Genital human papillomavirus (HPV) — a sexually transmitted infection — is the most common cause of cervical cancer. When a woman is exposed to HPV, her immune system usually prevents the virus from doing any serious harm. But in a small number of women, the virus survives for years. Eventually, the virus can lead to the conversion of normal cells on the surface of the cervix into cancerous cells.

At first, the cells may only show signs of a viral infection. Eventually, however, the cells may develop precancerous changes. This is known as cervical intraepithelial neoplasia. Typically, the precancerous changes go away spontaneously. In some cases, however — particularly for women who have altered immune systems — cervical intraepithelial neoplasia may eventually progress to invasive cervical cancer.

It's not clear why some women are more likely to develop cervical cancer. Some types of HPV are simply more aggressive than are others. Cigarette smoking also increases the risk of cervical cancer. In fact, according to the American Cancer Society, women who smoke are about twice as likely as nonsmokers to develop cervical cancer.

There are two HPV vaccines available — Gardasil and Cervarix. They offer protection from several of the most dangerous types of HPV. Gardasil is approved for boys and men, girls and women ages 9 to 26. Cervarix is approved for girls and women ages 9 to 25.

Remember, if you're sexually active, the best way to prevent HPV and other sexually transmitted infections is to remain in a mutually monogamous relationship with an uninfected partner. When you have sexual intercourse outside of a long-term monogamous relationship, always have your partner use a condom. Regular screening for cervical cancer and precancerous changes of the cervix is important, too.