Mounting research reveals the danger posed by a group of man-made chemicals developed in the 1930s that are resistant to water, heat, and oil. They’re used in paint, upholstery, cookware, carpeting, packaging, clothing, cosmetics, and more to make products nonstick, stain repellant, and waterproof. Among the health effects these products are linked to is the startling and little-discussed decline in human fertility. New research shows that these chemicals—per- and polyfluoroalkyl substances (PFAS)—aren’t only contaminating water and food, but also the air you breathe. There are more than 4,700 synthetic chemicals in the group with different properties and applications. In 1967, there was a deadly fire on the Navy aircraft carrier USS Forrestal, killing more than 130 sailors. Not long afterward, manufacturers developed a PFAS firefighting foam mixture that continues to be used to this day in the military and some fire departments. PFOA and PFOS are the most extensively studied …