DALLAS – In the United States, breast cancer is the most common cancer diagnosed among women.
While genetics and hormones shape a person’s risk for developing breast cancer, researchers have been investigating how environmental exposures – from air pollution to chemicals – may influence the disease over time. Here’s what to know.
What causes breast cancer?
Scientists can’t pinpoint a single cause for most breast cancers, but research shows risk is shaped by several factors.
Anywhere from 5% to 10% of breast cancers are due to inheriting harmful gene mutations, according to the Centers for Disease Control and Prevention. Mutations in the so-called breast cancer, or BRCA, genes are the most common; people who carry a BRCA mutation are estimated to be five to almost eight times more likely to develop breast cancer, according to a 2021 study in the New England Journal of Medicine.
Hormones also play a role. Women who begin menstruating early – especially before age 12 – and therefore have more menstrual cycles over their lifetime have a slightly higher risk for breast cancer, likely because they’re exposed to the hormones estrogen and progesterone for longer, according to the American Cancer Society. Those hormones act as a fuel for breast cancer cells, encouraging them to grow and spread.
How does the environment shape breast cancer risk?
A person’s breast cancer risk can be affected by environmental exposures. These may include tobacco smoke and certain chemicals that can mimic estrogen, such as compounds found in some plastics and pesticides.
Air pollution is another area of environmental exposure being studied. A 2025 study published in the American Journal of Public Health found that women living in parts of the United States with poorer air quality – especially neighborhoods with heavy vehicle emissions – had about a 3% higher risk of breast cancer. And a 2023 study from the National Institutes of Health found that living in areas with higher levels of particulate air pollution – a mix of tiny solid and liquid particles suspended in the air – was associated with a higher incidence of breast cancer.
The issue of air pollution is relevant in North Texas. Last year, the American Lung Association’s State of the Air report ranked the Dallas–Fort Worth area as the 10th worst metro out of the 25 most ozone-polluted regions in the nation. The report also found that 156 million people – about 46% of the U.S. population – live in areas with unhealthy levels of air pollution.
Other research has examined potential links between breast cancer and Superfund sites. These are abandoned or inactive locations, often former mines, landfills or manufacturing plants, where toxic chemical waste was never properly managed.
A 2025 study conducted by researchers with the Sylvester Comprehensive Cancer Center in Miami found an association between breast cancer severity and proximity to Superfund sites. Women who lived near a Superfund site were 27% more likely to be diagnosed with metastatic breast cancer than those who lived farther away.
Most research on environmental exposures and breast cancer has found associations rather than clear cause-and-effect relationships, in part because exposures are difficult to measure over long periods and often overlap with other risk factors. Still, some scientists, such as those at the NIH, are looking across a person’s lifetime to understand how environmental exposures might interact with genetics. The goal of this effort and other research is to strengthen public health protections and inform policies that reduce harmful exposures – and, ultimately, the burden of breast cancer.
Miriam Fauzia is a science reporting fellow at the Dallas Morning News. Her fellowship is supported by the University of Texas at Dallas. The News makes all editorial decisions.