Human papillomavirus (HPV) is one of the most common causes of sexually transmitted infection (STD) in the world. Health experts estimate that there are more cases of genital HPV infection than of any other STD in the United States. According to the American Social Health Association, approximately 5.5 million new cases of sexually transmitted HPV infections are reported every year. At least 20 million Americans are already infected.

Scientists have identified more than 100 types of HPV, most of which are harmless. About 30 types are spread through sexual contact. Some types of HPV that cause genital infections can also cause cervical cancer and other genital cancers.

Like many STDs, genital HPV infections often do not have visible signs and symptoms. One study sponsored by the National Institute of Allergy and Infectious Diseases (NIAID) reported that almost half of the women infected with HPV had no obvious symptoms. People who are infected but who have no symptoms may not know they can transmit HPV to others or that they can develop complications from the virus.

Genital warts (condylomata acuminata or venereal warts) are the most easily recognized sign of genital HPV infection. Many people, however, have a genital HPV infection without genital warts.

Some types of HPV cause common skin warts, such as those found on the hands and soles of the feet. These types of HPV do not cause genital warts.

Genital warts are very contagious and are spread during oral, genital, or anal sex with an infected partner. About two-thirds of people who have sexual contact with a partner with genital warts will develop warts, usually within three months of contact.

In women, the warts occur on the outside and inside of the vagina, on the opening (cervix) to the womb (uterus), or around the anus. In men, genital warts are less common. If present, they usually are seen on the tip of the penis. They also may be found on the shaft of the penis, on the scrotum, or around the anus. Rarely, genital warts also can develop in the mouth or throat of a person who has had oral sex with an infected person.

Genital warts often occur in clusters and can be very tiny or can spread into large masses in the genital or anal area.

A doctor or other health care worker usually can diagnose genital warts by seeing them on a patient. Women with genital warts also should be examined for possible HPV infection of the cervix.

The doctor may be able to identify some otherwise invisible warts in the genital tissue by applying vinegar (acetic acid) to areas of suspected infection. This solution causes infected areas to whiten, which makes them more visible, particularly if a procedure called colposcopy is performed. During colposcopy, the doctor uses a magnifying instrument to look at the vagina and cervix. In some cases, the doctor takes a small piece of tissue from the cervix and examines it under the microscope.

A Pap smear test also may indicate the possible presence of cervical HPV infection. In a Pap smear, a laboratory worker examines cells scraped from the cervix under a microscope to see if they are cancerous. If a woman's Pap smear is abnormal, she might have an HPV infection. If a woman has an abnormal Pap smear, she should have her doctor examine her further to look for and treat any cervical problems.

Genital warts often disappear even without treatment. In other cases, they eventually may develop a fleshy, small raised growth that looks like cauliflower. There is no way to predict whether the warts will grow or disappear. Therefore, if you suspect you have genital warts, you should be examined and treated, if necessary.

Depending on factors such as the size and location of the genital warts, a doctor will offer you one of several ways to treat them.

Imiquimod, an immune response cream which you can apply to the affected area
A 20 percent podophyllin anti-mitotic solution, which you can apply to the affected area and later wash off
A 0.5 percent podofilox solution, applied to the affected area but shouldn't be washed off
A 5 percent 5-fluorouracil cream
Trichloroacetic acid (TCA)

If you are pregnant, you should not use podophyllin or podofilox because they are absorbed by the skin and may cause birth defects in your baby. In addition, you should not use 5-fluorouracil cream if you are expecting.

If you have small warts, the doctor can remove them by freezing (cryosurgery), burning (electrocautery), or laser treatment. Occasionally, the doctor will have to use surgery to remove large warts that have not responded to other treatment.

Some doctors use the antiviral drug alpha interferon, which they inject directly into the warts, to treat warts that have returned after removal by traditional means. The drug is expensive, however, and does not reduce the rate that the genital warts return.

Although treatments can get rid of the warts, none gets rid of the virus. Because the virus is still present in your body, warts often come back after treatment.

Some types of HPV can cause cervical cancer. Others, however, cause cervical cancer and also are associated with vulvar cancer, anal cancer, and cancer of the penis (a rare cancer).

Most HPV infections do not progress to cervical cancer. If a woman does have abnormal cervical cells, a Pap test will detect them. It is particularly important for women who have abnormal cervical cells to have regular pelvic exams and Pap tests so that they can be treated early, if necessary.

Genital warts may cause a number of problems during pregnancy. Sometimes they get larger during pregnancy, making it difficult to urinate. If the warts are in the vagina, they can make the vagina less elastic and cause obstruction during delivery.

Rarely, infants born to women with genital warts develop warts in their throats (laryngeal papillomatosis). Although uncommon, it is a potentially life-threatening condition for the child, requiring frequent laser surgery to prevent obstruction of the breathing passages. Research on the use of interferon therapy in combination with laser surgery indicates that this drug may show promise in slowing the course of the disease.