Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a large group of human-made chemicals that have been used in industry and consumer products worldwide since the 1950s. Their ability to repel water and oil and withstand high temperatures has made PFAS a particularly useful ingredient in industrial and commercial products, including non-stick products, stain- and water-repellent clothing and fire-fighting foams. These chemicals do not easily break down in the environment and have been known to accumulate in the environment and humans. In a nationwide study, low levels of PFAS were determined to be present in the blood of most Americans. Two PFAS, perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS), are the most extensively studied of these chemicals.