With more than 600 million cases worldwide, including 20 million in the United States, human papillomavirus (HPV) is the most common sexually transmitted disease, according to the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO).

The virus is most prevalent among young adults. In a recent study, a research team led by Eduardo Franco at McGill University in Montreal, Quebec found that 56 percent of college-age women in new relationships were infected with the virus.

Why HPV is so common

HPV rates are high because most individuals do not realize they are infected, according to the CDC. In 90 percent of cases, there are no symptoms, and usually, the immune system is able to fight off the infection within a couple of years.

There are more than 40 types of HPV, however, and some can cause symptoms or lead to more serious conditions, such as genital warts and cervical cancer.

About 1 percent of sexually active people have genital warts from HPV these look like small bumps on the skin's surface. The warts typically develop within a few months of becoming infected. They can't be cured, but they are treatable and, in many instances, the warts go away on their own.

But the virus can also have more serious effects. Over many years, HPV can change normal cells into cancerous cells. Moreover, it's impossible to know if an HPV infection will definitively lead to cancer. In the Canadian study, Franco found that 44 percent of the subjects carried types of HPV that may cause cancer.

Each year, 12,000 American women are diagnosed with cervical cancer. It is the second deadliest cancer among women, according to the CDC, and annually kills 232,000 women around the world.

Can it be prevented?

The best protection against the disease is in the form of a relatively new vaccine called Gardasil, according to the CDC. The vaccine is recommended by the CDC for girls aged 11 to 12 and for boys aged 9 who aren't yet sexually active.

Gardasil, which is made by Merck & Co., protects against two types of HPV that may cause cervical cancer and it protects against two types that cause genital warts. Older women and men can still receive the vaccine, but it is most effective if given early. Even with the vaccine, women should still undergo routine screening for cervical cancer.

Another vaccine is also available. This vaccine, called Cervarix and made by GlaxoSmithKline, protects against two strains that can lead to cervical cancer.

Got a question? Email it to view it to Life's Little Mysteries and we'll try to answer it. Due to the volume of questions, we unfortunately can't reply individually, but we will publish answers to the most intriguing questions, so check back soon.