The chemicals Lee is referencing—perfluorooctanesulfonate, or PFOS, and perfluorooctanoic acid, PFOA—are two kinds of long-chain PFAS. These chemicals were widely used until 2011, when manufacturers started voluntarily phasing them out because of concerning health risks. Studies have found links between exposure and cancer, birth defects, and thyroid dysfunction. The worst health risks are associated with high levels of exposure, which you might get from working in a factory that used PFOS and PFOA. But the reason these long-chain compounds are worrisome for everyone is because they never break down, and they accumulate in your body—the half life of PFOS in the human body is four to six years.