(Reuters Health) - Women who reported douching almost doubled their risk of developing ovarian cancer, a national U.S. study shows.

Prior studies have linked douching, or vaginal washing with a device, to yeast infections, pelvic inflammatory disease and ectopic pregnancies. Researchers have also found associations between douching and cervical cancer, reduced fertility, HIV and other sexually transmitted diseases.

But the new National Institute of Environmental Health Sciences study is the first to tie cancer of the ovaries to the procedure routinely practiced by millions of American women.

Joelle Brown, an epidemiology professor at the University of California, San Francisco said that although she knew about other health problems associated with douching, the link between douching and ovarian cancer took her by surprise.

“While most doctors and the American College of Obstetricians and Gynecologists strongly recommend that women do not douche, many women continue to douche because they falsely perceive douching to have positive health benefits, such as increased cleanliness,” she told Reuters Health by email. Brown was not involved in the current study.

Interventions to encourage women not to douche are needed, she said.

Ovarian cancer is known as “the silent killer” because women often experience no symptoms until the disease has progressed to an advanced stage. An estimated 20,000 American women are diagnosed with ovarian cancer and about 14,500 die from it annually, according to the Centers for Disease Control and Prevention (CDC).

The new analysis in the journal Epidemiology followed more than 41,000 women throughout the U.S. and Puerto Rico since 2003 as part of the Sister Study. Participants were 35 to 74 years old, and each had a sister who had been diagnosed with breast cancer. The subjects were free of breast and ovarian cancer when they enrolled in the study.

By July 2014, researchers counted 154 cases of ovarian cancer among participants. Women who reported douching during the year before entering the study nearly doubled their risk of ovarian cancer, the study found.

The link between douching and ovarian cancer was even stronger when the authors looked only at women who didn’t have breast-cancer genes in their family.

No study had ever before examined a possible relationship between douching and ovarian cancer, senior author Clarice Weinberg said in a telephone interview. She is deputy chief of the biostatistics and computational biology branch at the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina.

“There are a number of health reasons not to douche, and I can’t think of any reason to do it,” she said.

Vaginas naturally clean themselves, and squirting cleansers or other mixtures inside the canal only interferes with nature’s balance. Douching can cause an overgrowth of harmful bacteria, lead to yeast infections, and push bacteria up into the uterus, fallopian tubes and ovaries, according to the Office on Women’s Health at the U.S. Department of Health and Human Services (HHS).

Nevertheless, one quarter of women between the ages of 15 and 44 douche, HHS says.

Brown, who led a 2016 study published in PLoS One that examined women’s motivations for douching, said she has long been fascinated by the display of so-called feminine hygiene products lining drugstore shelves.

“In most pharmacies you can find entire aisles dedicated to vaginal douches, suppositories and gels that are meant to make your vagina smell like a tropical splash or a cookie,” she said.

Women douched as far back as 1500 B.C., when an Egyptian papyrus recommended intravaginal washing with garlic and wine to treat menstrual disorders. American women once douched with Lysol, and some mistook the toilet bowl disinfectant for birth control.

Women often learn to douche from their mothers, Brown’s study found. They do so because they see douching as a necessary part of good hygiene, to prepare for sex, to clean up after sex and at the urging of their male partners.

Despite medical recommendations, douching remains a common practice because women “believe that the products they are using would not be for sale or recommended by their mothers if they were not safe,” Brown said.

“In general, I think women do not realize that douching products do not fall under the same kind of safety regulation as drugs,” she said. “Instead, douching products are considered cosmetics, which means that the U.S. Food and Drug Administration does not require that douche manufacturers test their products for safety.”

SOURCE: bit.ly/29UeRFD Epidemiology, online June 20, 2016.