Do Underwire Bras Cause Breast Cancer?

In 1995 two authors, Sydney Ross Singer and Soma Grismaijer, published a book called Dressed to Kill. Its argument was short enough to repeat at a party. Bras squeeze the breast. That squeezing blocks the lymph system, the network of vessels that drains fluid out of tissue. Waste piles up with nowhere to go. Breast cancer follows.

The book reported that women who wore a bra most of the day had far higher rates of breast cancer than women who rarely wore one. Three decades later that claim is still being posted, filmed, and shared.

It has since been tested by researchers who had no stake in the book. It did not hold up.

The place to start is the study design, because that is where the argument comes apart.

Dressed to Kill rested on a survey. The authors asked women about their bra habits and compared answers between women who had breast cancer and women who did not. That is not the same as a controlled study, and two problems sink it.

The first is recall bias. The authors already believed the conclusion before they gathered a single answer. People who have been diagnosed with a serious illness also tend to search their own past harder for a cause than healthy people do. Ask two groups to remember decades of clothing habits and you will get a difference, whether or not one exists.

The second problem is bigger, and it is worth naming carefully. A confounder is a third factor that creates an apparent link between two things that are not actually connected. Bra wearing has an obvious one. Women who go without a bra for most of the day tend to have smaller breasts, and breast size tracks with overall body size.

Body weight is not a neutral variable here. The American Cancer Society states that "having excess body weight (overweight or obesity) after menopause increases breast cancer risk," and explains why: after menopause the ovaries stop making estrogen, so "most estrogen then comes from fat tissue." More fat tissue means more estrogen, and estrogen drives many breast cancers.

So a survey comparing bra wearers with non-wearers is partly comparing heavier women with lighter women. Any real effect of weight would show up looking like an effect of bras. The book did not account for that.

The mechanism behind the claim also needs a look, because it is stated with more confidence than the biology supports.

Lymph nodes are, as the American Cancer Society describes them, "small structures that work as filters for foreign substances, such as cancer cells and infections." The vessels feeding them carry lymph, a clear watery fluid that also contains white blood cells. Those vessels "draw up the lymph fluid from around the cells to send it towards the chest," where it empties into a blood vessel near the heart.

Notice the direction. Lymph from the breast moves inward and upward, mostly toward the nodes under the arm and then on toward the chest. It is not being pushed out through the skin. There is no exit through the surface that a bra could seal.

The "trapped toxins" half of the story has been answered too. Sweat glands, the same ACS review notes, "mainly cool the body, rather than remove toxins." The substances that could cause cancer are cleared from the blood by the kidneys and the liver and leave in urine and stool.

A bra can leave a red mark. That is pressure on skin, not a blocked drain. Real blockage of lymph flow does exist, and it has a name: lymphedema, the arm swelling some people get after underarm lymph nodes are removed or treated with radiation. It looks nothing like wearing a bra, and it is not a cause of cancer. It is a side effect of cancer treatment.

In 2014 researchers at Fred Hutchinson Cancer Center published the study the claim had been waiting for. Lu Chen, Kathleen Malone, and Christopher Li interviewed 1,044 women aged 55 to 74 who had invasive breast cancer, and compared them with 469 women of the same ages who did not.

The interviews covered hours of bra wear per day, whether the bra had an underwire, the age at which the woman started wearing one, and her pattern of wear across her lifetime. That is exactly the set of details the book had claimed mattered.

Nothing showed up. In the study team's words: "Our study found no evidence that wearing a bra increases a woman's risk for breast cancer. The risk was similar no matter how many hours per day women wore a bra, whether they wore a bra with underwire, or at what age they began wearing a bra."

The American Cancer Society's own review of disproven breast cancer risk factors reaches the same place: "There is no scientific or clinical data that shows that wearing a bra changes the risk of having breast cancer. This data includes a 2014 study of more than 1,500 women."

Breast cancer is common. The National Cancer Institute estimates that 12.9% of women born in the United States today will develop it at some point, roughly 1 in 8. Men are not exempt, though the lifetime risk is about 0.13%, or 1 in 800.

The factors that genuinely move that number are well studied. Age is the largest. Family history and inherited gene changes such as BRCA1 and BRCA2 matter. So do hormone-related factors: an early first period, late menopause, having a first child later or not at all, and certain forms of menopausal hormone therapy.

Three items on the list are ones you can act on. Alcohol raises risk, and ACS notes "the risk increases the more alcohol you drink," recommending women have no more than one drink a day. Excess body weight after menopause raises risk. And physical activity lowers it: ACS advises adults get 150 to 300 minutes of moderate activity, or 75 to 150 minutes of vigorous activity, each week.

Underwire does not appear anywhere on that list.

The practical advice here is unusually short. Choose the bra that is comfortable. Wear it as long as you like, or skip it. A bra that digs in or leaves welts is worth replacing because it hurts, not because it is dangerous.

There is one thing worth guarding, and it is your attention. The hours some people spend worrying about underwire would be better spent on the things that change outcomes: keeping to the screening schedule your clinician recommends, getting a new lump or skin change looked at without delay, and knowing whether breast or ovarian cancer runs in your family. That last one can change what screening you are offered and when it starts.

If someone sends you the bra claim, you can now answer with more than a shrug. You can say who wrote the book, what its survey could not control for, how the 2014 study was built, and what it found.

• https://www.cancer.org/cancer/types/breast-cancer/risk-and-prevention/disproven-or-controversial-breast-cancer-risk-factors.html
• https://www.fredhutch.org/en/news/center-news/2014/09/Bras-dont-cause-breast-cancer-hutch-study.html
• https://www.cancer.org/cancer/diagnosis-staging/lymph-nodes-and-cancer.html
• https://www.cancer.org/cancer/risk-prevention/chemicals/antiperspirants-and-breast-cancer-risk.html
• https://www.cancer.org/cancer/types/breast-cancer/risk-and-prevention/lifestyle-related-breast-cancer-risk-factors.html
• https://www.cancer.gov/types/breast/risk-fact-sheet