Certain HPV types are classified as "high-risk" because they lead to abnormal cell changes and can cause genital cancers: cervical cancer as well as cancer of the vulva, anus, and penis. In fact, researchers say that virtually all cervical cancers -- more than 99% -- are caused by these high-risk HPV viruses. The most common of the high-risk strains of HPV are types 16 and 18, which cause about 70% of all cervical cancers.
If the body clears the infection, the cervical cells return to normal. But if the body doesn't clear the infection, the cells in the cervix can continue to change abnormally. This can lead to precancerous changes or cervical cancer.
When infection with high-risk HPV types occurs, there are usually no symptoms. Often, the first clue is a Pap test result that is abnormal. In a Pap test, the doctor takes a swab of cervical cells and has them analyzed in a laboratory. If the Pap test results are unclear, the doctor may order a HPV test to check the DNA type of the virus.