Per- and polyfluoroalkyl substance (PFAS) are a class of chemicals linked to cancer, liver damage, thyroid disease, and developmental issues. The chemicals became popular in the US around the 1940s, when manufacturing companies realized they resist heat, grease, stains, and water.
Since then, scientists have discovered that PFAS can linger in water and air for thousands of years, landing them the nickname "forever chemicals." Consuming or inhaling them means they could stay in the body for life.
A 2015 study from the Harvard School of Public Health found that breastfeeding is "an important exposure pathway" for PFAS in infants. According to the researchers, an infant's PFAS concentrations can increase up to 30% for every month that they're breastfed.
Another study, published in 2018, detected breast milk with PFAS among sample populations in at least 19 countries.