Genital warts are caused by the human papilloma virus (HPV). Papilloma viruses cause small growths (warts) on the skin and mucous membranes. Infection of the genital and anal regions with HPV can cause warts (anogenital condyloma) on the penis, vulva, urethra, vagina, cervix, and around the anus (perianal).

More than 70 different types of HPV have been classified. Several types, including 6, 11, and 42, are associated with raised, rough, easily visible genital warts (especially in women).

Other types are associated with flat warts. More importantly, several types are associated with pre-malignant and malignant changes in the cervix (abnormal Pap smears). These include types 16, 18, 31, 33, 35, 39, 45, 51, and 52. Research also shows that the presence of both HPV and herpes virus together is a good predictor of cervical cancer.

Lesions on the external genitalia are easily recognized. On the penis, genital warts tend to be drier and more limited than on the female genitalia or around the anus of either sex.

They grow best in the moist genital area. They are raised, rough, flesh-colored "warty" appearing tumors that may occur singly or in clusters. Left untreated, warts around the anus and vulva may rapidly enlarge, taking on a "cauliflower-like" appearance. Keeping the infected area dry may be a problem because the warts are usually damp.

In women, HPV can invade the vagina and cervix. These warts are flat and not easily visible without special procedures. Because HPV can lead to premalignant changes in the cervix (cervical dysplasia), it is important that this condition be diagnosed and treated. Regular Pap smears are important for detecting HPV.

Infection with HPV is very common, although the majority of people have no symptoms (asymptomatic). In several studies done on college women, nearly half were positive for HPV; although only 1 to 2% had visible warts and less than 10% had ever had any visible genital warts. The incidence of genital warts appears to be increasing rapidly, although this may be a result of increased diagnostic ability and awareness.

Risk factors for genital warts include multiple sexual partners, unknown partners, early onset of sexual activity, tobacco use, nutritional status, hormonal conditions, age, stress and concurrent viral infections (such as flu, HIV, Epstein-Barr and herpes).

In children, although the virus can be transmitted sexually, non-sexual transmission is possible, particularly if the child is still in diapers. The presence of genital warts (condylomata acuminata) should raise the question of sexual abuse. However, if all of the following are true, then non-sexual transmission is more likely:

• the warts are somewhat distant from the anal or vaginal openings
• the warts are present in close contacts (especially genital warts in the mother or primary caretaker)
• the child is younger than 9 months at the time the warts first appear
• there is no evidence for child abuse