PFAS chemicals found in firefighting foam can cause serious birth defects and health effects. PFAS refers to thousands of man-made compounds used in countless products, including nonstick cookware, water-repellent sports gear, cosmetics and grease-resistant food packaging, along with firefighting foams. Public health studies on exposed populations have associated the chemicals with an array of health problems, including some cancers, weakened immunity and low birth weight. Widespread testing in recent years has found high levels of PFAS in many public water systems. They're called “forever chemicals” because they don't degrade in the environment. PFAS substances have been found in groundwater on or near more than 300 military bases, according to the nonprofit Environmental Working Group.