But a new and rigorous examination of the issue concludes that "no aspect of bra wearing, including bra cup size, recency, average number of hours [per]day worn, wearing a bra with an underwire, or age first began regularly wearing a bra, was associated with risks of either [invasive ductal carcinoma] or [invasive lobular carcinoma] breast cancer."
The study by researchers at the Fred Hutchinson Cancer Research Center in Seattle was conducted because "we saw those rumors on the Internet and we had the data to examine this in a scientific way," said Lu Chen, a researcher at the facility and a doctoral student at the University of Washington department of epidemiology, who led the team. It compared 454 women post-menopausal women with invasive ductal carcinoma and 590 women with invasive lobular carcinoma diagnosed between 2000 and 2004 with 469 women who did not have cancer. The women, who were 55 to 74 years old, were asked about their bra-wearing habits as part of a much larger examination of breast cancer risk factors funded by the National Cancer Institute.
The reasoning behind the cancer myth is that a bra, particularly one with underwire, somehow blocks the flow of lymph to an area beneath the armpit where bacteria and other waste products would normally be cleared from around the breast. It's not clear how it began, but many note a 1995 book "Dressed to Kill" which pointed out an association between lower breast cancer rates in societies where women don't wear bras and higher rates in cultures where they do. It did not examine other possible explanations.
"This is a common confusion," said Chen. "They see two things happening at the same time and they think one causes the other."
The 1991 study found that women who go braless had fewer breast cancers, but the difference wasn't statistically significant. And the researchers suggested that the correlation might be because those women are leaner; obesity is a known risk factor for breast cancer.
Chen suggested that the lack of research since then is probably because the idea of bras causing cancer "seemed so implausible, so people didn’t look at it." When she finally did, her research was able to establish that there is no connection.
"It was one of the myths going around on the Internet," she said. "But this notion has no scientific basis."