Do Underwire Bras Cause Breast Cancer?

This page is for anyone who has heard that underwire bras cause breast cancer. It covers where the idea came from, how it was tested, and what actually affects breast cancer risk.

A 1990s book, Dressed to Kill, popularized the idea. 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. The claim is still being posted and shared.

It has since been tested, and it did not hold up.

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

The book 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. 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 confounding. A confounder is a third factor that can create an apparent link between two things that are not connected. Body weight is a known risk factor. The American Cancer Society says excess weight after menopause increases breast cancer risk. It explains that "most estrogen then comes from fat tissue," and that more fat tissue can raise estrogen levels.

A survey like this one can mix up bra habits with other differences between women, such as body weight. That makes it weak evidence.

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 moves toward the chest, not out through the skin. There is no exit on the surface that a bra could seal.

The "trapped toxins" half of the story has been answered too. In its page on antiperspirants, the American Cancer Society notes that sweat glands in the skin, including under the arms, "mainly cool the body, rather than remove toxins."

A bra can leave a red mark. That is pressure on skin, not a blocked drain.

A 2014 study of more than 1,500 women looked at this question. The American Cancer Society cites it in its review of disproven breast cancer risk factors. That review says: "There is no scientific or clinical data that shows that wearing a bra changes the risk of having breast cancer."

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.

Many factors move that number. NCI says risk rises with age. Family history and inherited gene changes also matter. The American Cancer Society lists hormone-related factors too, such as having a first child after age 35 or never being pregnant, and some hormone treatments.

Three items on the list are ones you can act on. Alcohol raises risk. ACS says the risk rises with the amount you drink. It advises women to have no more than 1 drink a day, and notes that no amount of alcohol is completely safe. Excess body weight after menopause raises risk. And ACS says regular physical activity lowers risk: 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
• 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 what the book's survey could not control for and what the 2014 study found, as reported by the American Cancer Society.

• https://www.cancer.org/cancer/types/breast-cancer/risk-and-prevention/disproven-or-controversial-breast-cancer-risk-factors.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