It's one of those absurd, persistent myths that keeps spreading around the Internet, but that an epidemiological study has now put to rest: no, bras do not cause breast cancer.

For years, rumours have swirled that the reason breast cancer is more common in developed countries than in developing countries is because more women in richer countries wear bras.

A book published in 1995, called "Dressed To Kill: The Link Between Breast Cancer and Bras," even suggested that bras increase a woman's cancer risk because they hamper the drainage of toxins through the lymph nodes near the breast.

It's a theory many women have suggested they thought might be true. In 2002, American Cancer Society researchers released a survey that found six per cent of respondents believed that "underwire bras can cause breast cancer,” while another 31 per cent were not sure.

For this study, a team at the Fred Hutchinson Cancer Research Center in Seattle studied more than 1,000 post-menopausal women living in the Seattle area who had been diagnosed with invasive breast cancer between 2000 and 2004. The women were compared to women without breast cancer.

The researchers also held in-person interviews to ask the women about their lifetime bra-wearing habits.

No matter how many ways the researchers looked at the numbers, they could find absolutely no link between how often women wore bras and their risk of developing breast cancer. The risk was the same no matter how many hours per day women wore a bra, whether they wore a bra with an underwire, or at what age they first began wearing a bra.

“We weren’t really surprised,” said Fred Hutchinson researcher Lu Chen, a doctoral student at the University of Washington School of Public Health.

“We knew that the biological plausibility of a link between bras and breast cancer was really weak.”

The full study is published this month in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research. The study was funded by the U.S. National Cancer Institute.

Still, one of the authors of “Dressed to Kill,” Sydney Ross Singer, is not convinced.

Singer questioned why the researchers studied only post-menopausal women rather than all women, suggesting in an email to the Fred Hutchinson Center that the researchers' conclusion “suggests a pro-bra bias.”

The researchers respond they used data from post-menopausal breast cancer patients because most breast cancers are diagnosed in older women. They also have worn bras the longest.

The American Cancer Society has addressed the breast-breast cancer myth in the past and says it's important that women understand the risk factors that are known to increase the risk for breast cancer.

They include factors that can't be controlled, such as aging (the risk of all cancer increases with age); genetic factors, and simply being a woman. Known risk factors that can be controlled include maintaining a healthy weight; reducing or avoiding alcohol; and bearing children before the age of 30.