Summary: Women whose partners use condoms every time they have sex are less likely to become infected with HPV, the virus that can cause cervical cancer and genital warts, than women who only occasionally use them. Consistent condom use cut a woman's risk of infection by 70% and protected her from developing precancerous cervical changes, according to a University of Washington study published in the New England Journal of Medicine.

Why it's important: HPV, or human papilloma virus, is a very common virus. There are more than 30 strains that can be transmitted through sexual contact. Millions of Americans become infected with one of these strains every year, but most never know it because the virus usually causes no symptoms and the body gets rid of the infection on its own. Sometimes, though, the virus doesn't go away, and certain strains of the virus can eventually cause genital warts or cervical cancer.

The Gardasil vaccine which was recently approved for use in young women and girls, can protect women against 4 strains of the virus that cause nearly all cases of genital warts and about 70% of cervical cancers. But the vaccine does not protect against the many other strains of HPV that can cause cancer or warts. This study shows that condoms are another tool women can use to protect themselves from HPV and the diseases it can cause.

What's already known: Aside from helping prevent unintended pregnancy, condoms have been shown to help reduce the risk of several sexually transmitted diseases, including HIV, the virus that causes AIDS. But there has been some controversy over just how much protection condoms might offer women from HPV. Studies done in the past did not show a great benefit for preventing HPV infection, although some large ones did find that condom use seemed to reduce the chances of women developing precancerous changes in the cervix. But those studies had many design flaws that made it difficult to rely on their findings. For instance, they were based on people's memories of how often they used condoms (always, sometimes, or never) over a long period of time in the past.

How this study was done: The new study was designed to address those shortcomings. The researchers studied only young women (college students age 18 and older) who had never had sex before, or who'd had their first sexual encounter within 3 months of the study's start. By restricting participation in this way, the researchers lowered the chance of a woman having a previous HPV infection that might skew results by flaring up during the study, even though she didn't acquire it during the study. The researchers also asked the women to keep daily online diaries tracking how often they had sex, whether their partner used a condom, and whether they had a new partner. That gave the researchers a much more precise measure of condom usage. All the women had a Pap test and HPV test at the beginning of the study, and every 4 months for the next year.

That careful design makes the study "immensely important" even though only 82 women took part, said gynecologist Tom Cox, MD. He is director of the women's health clinic at the University of California, Santa Barbara, Student Health Service and a member of the committee that developed the American Cancer Society's guidelines for cervical cancer detection. He was not involved in the University of Washington study.

"It's not a huge study, but it's people who were followed so intensely and had such strict parameters of entry into the study that it markedly increases the value of the results," he explained.

What was found: Women who reported using condoms 100% of the time had a dramatically lower rate of HPV infection than women who said they used condoms only 5% of the time or less. The consistent condom users were 70% less likely to become infected. Even inconsistent use helped; women who used condoms only half the time cut their risk of HPV infection by 50%.

What's more, no cervical precancers were found among women who used condoms 100% of the time, but 14 precancers were detected in the women who used condoms 5% of the time or less.

"It certainly gives individuals one more reason to use condoms all the time, at least until they're in a relationship that they consider to be beyond the pale of being at risk for sexually transmitted diseases," said Cox.

It's important to note, though, that condom use wasn't 100% effective in protecting against HPV. One reason is that the virus can be transmitted by skin-to-skin contact and may linger in areas that don't get covered by a condom. Another is that people don't always use condoms correctly.

The bottom line: Young women should use condoms every time they have sex and doctors should encourage them to do so, while also reminding them of other ways to protect themselves from HPV, said lead study researcher Rachel Winer, PhD.

"Using condoms can reduce your risk of [HPV] infection significantly," said Winer, an epidemiology instructor at the University of Washington. "But given that it's not 100%, it's still important that women who are able to get vaccinated [against HPV] get vaccinated. And even if they use condoms and get vaccinated it's still important to get screened for cervical cancer."

Cox agrees. Neither condoms nor the HPV vaccine offer complete protection against every HPV type that could cause cervical cancer, so regular screening with Pap tests is still crucial to preventing the disease.

"Cervical screening has to continue," he said. "Women are still at risk."

Citation: "Condom Use and the Risk of Genital Human Papillomavirus Infection in Young Women." Published in the June 22, 2006 ,New England Journal of Medicine (Vol. 354, No. 25: 2645-2654). First author: Rachel Winer, PhD, University of Washington HPV Research Group.