Human papillomaviruses are double-stranded DNA viruses found in squamous epithelial cells on the surface of the skin and also in the mucous membranes of the body.⁽¹⁾ There are more than 200 known types of human papillomavirus (HPV), and most are harmless.⁽²⁾ In most cases, the human immune system clears HPV infections without symptoms or complications.⁽³⁾

Over 90% of infected people naturally clear the infection from their bodies within two years.⁽⁴⁾ Antibodies from the type of HPV that caused the infection remain in the body to help prevent future infections, but the protection may not last.⁽⁵⁾

Low-risk HPV types - About 75% of HPVs have been associated with noncancerous warts (papillomas) on the hands, chest, arms, and feet, such as low-risk (wart-causing) HPV types 6 and 11.⁽⁶⁾ The low-risk HPV types associated with genital warts differ from the high-risk HPV types that may be associated with cancer development after years of chronic infection.⁽⁷⁾

High-risk HPV types - Approximately 40 types of HPV have been found in the mucous membranes of the body, such as the mucous surfaces of the cervix, vagina, vulva, anus, penis, mouth and throat, including the most common HPV types such as high risk 16 and 18. High-risk HPV types are associated with cervical cancer and five other types of genital and oral cancers that affect women and men if the HPV infection does not heal and becomes an infection chronic.⁽⁸⁾ High-risk HPV types currently include types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 69, 73, and 82.⁽⁹⁾

The National Cancer Institute states that "virtually all cervical cancers are caused by HPV infections, and just two types of HPV, HPV 16 and 18, are responsible for about 70 percent of all cases."⁽¹⁰⁾ HPV type 16 causes 95% of all anal cancers, 50% of all vulvar cancers, 65% of all vaginal cancers, 35% of all penile cancers, and more than half of oropharyngeal cancers in the United States.⁽¹¹⁾