Per- and polyfluoroalkyl substances (PFAS) are a large group of human-made chemicals that have been used in various industrial applications and consumer products since the 1940s. These chemicals are resistant to water, grease, and stains, making them ideal for products like non-stick cookware, water-repellent clothing, and firefighting foams. PFAS are often referred to as "forever chemicals" due to their persistent nature in the environment.