Papillomaviruses are a diverse group of DNA-based viruses that infect the skin and mucous membranes of humans and a variety of animals. Over 100 different human papillomavirus (HPV) types have been identified.

Some HPV types may cause warts while others may cause a subclinical infection resulting in precancerous lesions. All HPVs are transmitted by skin-to-skin contact.

A group of about 30-40 HPVs is typically transmitted through sexual contact and infect the anogenital region. Some sexually transmitted HPVs may cause genital warts. However, other HPV types which may infect the genitals do not cause any noticeable signs of infection.

Persistent infection with a "high-risk" subset of sexually transmitted HPVs — different from the ones that cause warts — may lead to potentially precancerous lesions and can progress to invasive cancer. HPV infection is a necessary factor in the development of nearly all cases of cervical cancer.

A cervical Pap smear is used to detect cellular abnormalities. This allows targeted surgical removal of condylomatous and/or potentially precancerous lesions prior to the development of invasive cervical cancer. Although the widespread use of Pap testing has reduced the incidence and lethality of cervical cancer in developed countries, the disease still kills several hundred thousand women per year worldwide. A recently approved HPV vaccine, Gardasil, that blocks initial infection with four of the most common sexually transmitted HPV types may lead to further decreases in the incidence of HPV-induced cancer.