Doctors have long recommended that women do not douche, yet the practice continues, inexplicably. One quarter of women between the ages of 15 and 44 douche, according to the Office on Women’s Health at the U.S. Department of Health and Human Services. Perhaps a new study that show women who reported douching almost doubled their risk of developing ovarian cancer will be the final coffin nail.

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.

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 told Reuters. 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.