Clothing that's "waterproof" or "stain resistant" might seem like a bonus, but these words could be a tip-off that an item contains a toxic class of chemicals called per- and polyfluoroalkyl substances (PFAS).
PFAS became popular in the US around the 1940s when manufacturing companies realized they could resist heat, grease, stains, and water. They're often referred to as "forever chemicals" since they can linger in the environment for thousands of years.
Though many PFAS have been phased out of the manufacturing industry, the chemicals can still be found in leather and textiles. Labels that contain the words Gore-Tox or Teflon may signal the presence of PFAS, which are commonly found in outdoor gear and "moisture-wicking" workout clothes.
Exposure to PFAS has been associated with kidney and testicular cancers, liver damage, and developmental issues, but humans are more likely to be exposed by ingested contaminated food or drinking water.
The Centers for Disease Control (CDC) considers skin contact a "minor" source of exposure, though breathing in dust from PFAS-contaminated clothing can also constitutes "low level exposure."