Updated Nov. 11, 2008 – Human papillomavirus (HPV) is a highly contagious sexually transmitted disease, but many people don’t know what it is or how common it is. And, since, many of types of HPV show no symptoms, most people don’t even know whether they have it or not.

“The most important thing to know is that it is very, very common,” said Dr. Cynthia Paige, MD., assistant professor of Family Medicine at the University of Medicine And Dentistry of New Jersey. “The risk goes up with the greater number of partners you have and with unprotected sex.”

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 Here’s are more facts about HPV from the U.S. Centers for Disease Control:

What is HPV? Genital HPV infection is a sexually transmitted disease (STD) that is caused by human papillomavirus (HPV). Human papillomavirus is the name of a group of viruses that includes more than 100 different strains or types. More than 30 of these viruses are sexually transmitted, and they can infect the genital area of men and women including the skin of the penis, vulva (area outside the vagina), or anus, and the linings of the vagina, cervix, or rectum. Most people who become infected with HPV will not have any symptoms and will clear the infection on their own, but there can be lasting and irreversible damage, such as cancer of the cervix, penis or vagina or genital warts, which are single or multiple growths or bumps that appear in the genital area, and sometimes are cauliflower shaped.

How common is HPV? Approximately 20 million people are currently infected with HPV. At least 50 percent of sexually active men and women acquire genital HPV infection at some point in their lives. By age 50, at least 80 percent of women will have acquired genital HPV infection. About 6.2 million Americans get a new genital HPV infection each year.

How do you get HPV? The types of HPV that infect the genital area are spread primarily through genital contact during sex. Most infected persons are unaware they are infected, yet they can transmit the virus to a sex partner.

What are the symptoms? Most people who have a genital HPV infection do not know they are infected. The virus lives in the skin or mucous membranes and usually causes no symptoms. However, some forms of the disease produce visible genital warts, or pre-cancerous changes in the cervix, vulva, anus, or penis. Very rarely, HPV infection results in anal or genital cancers. Genital warts are diagnosed by visual inspection.

How do you know if you have it? Most women are diagnosed with HPV when they have an abnormal Pap tests or HPV test. A Pap test is the primary cancer-screening tool for cervical cancer or pre-cancerous changes in the cervix, many of which are related to HPV. Also, a specific test is available to detect HPV DNA in women. The results of HPV DNA testing can help health care providers decide if further tests or treatment are necessary. Right now, there is no test for men to determine if they have HPV.

How do you avoid HPV? The best way to avoid HVB is not to have sex, thus avoiding genital contact with another individual. If you are sexually active, being in a long-term relationship with one, uninfected partner is the best strategy to prevent future genital HPV infections. However, it is difficult to tell whether a partner who has been sexually active in the past is currently infected. Use a condom. Condom use has been shown to lower the rate of cervical cancer, a disease associated with HPV.

Don’t be fooled into thinking you’re completely safe with a condom, though, or with the new HPV vaccine, Dr. Paige says. While condoms provide the best protection if you are sexually active, they are not 100 percent foolproof.  You could still get HPV from an infected partner if you are not careful to protect yourself.

“You can look at your partner to see if he or she has little lesions, or bumps on his penis or genitals, but there are different types of HPV. Some cause raised lesions. But, the viral types that cause the warts don’t lead to cancer. The types that leads to cancer may not have any lesion at all,” Dr. Paige explains. “Also, 70 percent of genital cancers you get may be prevented by having the HPV vaccine, but about the 30 may not. If you’re sexually active you need a PAP smear once-a-year. That’s what will protect you from cervical cancer.”

For more on HPV, go to the American Social Health Association's HPV site.