Human Papilloma Virus (HPV), Cancer, HPV Testing, and HPV Vaccines : Frequently Asked Questions

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What is HPV?

HPV is short for human papilloma (pap-uh-LO-muh) virus. HPVs are a group of more than 150 related viruses. Each HPV virus in the group is given a number, which is called an HPV type. HPVs are called papilloma viruses because some of the HPV types cause warts or papillomas, which are non-cancerous tumors.

The papilloma viruses are attracted to and are able to live only in squamous epithelial cells in the body. Squamous epithelial cells are thin, flat cells. They are found in the surface of the skin and in moist surfaces like the vagina, anus, cervix (the base of the womb at the top of the vagina), vulva (around the outside of the vagina), head of the penis, mouth, throat, trachea (the main breathing tube), bronchi (smaller breathing tubes branching off the trachea), and lungs. HPVs will not grow in other parts of the body.

Of the more than 150 known strains, about 3 out of 4 (75%) HPV types cause warts on skin, such as that of the arms, chest, hands, and feet. These are the common warts.

The other 25% of the HPV types are mucosal types of HPV. “Mucosal” refers to the body’s mucous membranes, or the moist surface layers that line organs and cavities of the body that open to the outside. For example, the vagina and anus have this moist mucosal layer. The mucosal HPV types are also called the genital (or anogenital) type HPVs because they often affect the anal and genital area. The mucosal HPVs prefer the moist squamous cells found in this area. They do not often grow in the skin.

Low-risk HPV types

Some types of genital HPV can cause cauliflower-shaped warts on or around the genitals and anus of both men and women. In women, warts may also appear on the cervix and vagina. This type of genital wart is called a condyloma acuminatum and is most often caused by HPV-6 or HPV-11. Because these genital warts very rarely grow into cancer, HPV-6 and HPV-11 are called low-risk viruses. These low-risk types can also cause low-grade changes in the cells that do not develop into cancer.

High-risk HPV types

Other types of genital HPV have been linked with cancers in both men and women. These types are called high-risk because they can cause cancer. They also cause low-grade and high-grade changes in the cells and pre-cancers. Doctors worry more about the high-grade changes and pre-cancers, because they are more likely to grow into cancers over time. Common high-risk HPV types include:

  • HPV-16
  • HPV-18
  • HPV-31
  • HPV-33
  • HPV-35
  • HPV-39
  • HPV-45
  • HPV-51
  • HPV-52
  • HPV-58
  • HPV-59
  • HPV-68

Warts and cancer are caused by different types of HPV

In summary, low-risk HPV types can cause genital warts and low-grade changes in the cells, but rarely cause cancer. High-risk HPV types can cause low-grade changes, high-grade changes, pre-cancer, and cancer.

This diagram shows the different groups of HPV types and the problems each group can cause.

Last Medical Review: 05/02/2013
Last Revised: 05/02/2013