Per- and polyfluoroalkyl substances (PFAS or PFASs) are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain. The PubChem database lists more than 6 million unique compounds in this group. PFASs started being used in the mid-20th century to make fluoropolymer coatings and products that resist heat, oil, stains, grease, and water. They are used in a variety of products including waterproof clothing, furniture, adhesives, food packaging, heat-resistant non-stick cooking surfaces, and the insulation of electrical wire. They have played a key economic role for companies such as DuPont, 3M, and W. L. Gore & Associates that use them to produce widely known materials such as Teflon or Gore-Tex. 
Only since the start of the 21st century has the environmental impact and toxicity to human and mammalian life been studied in depth. Many PFAS such as PFOS, PFOA are a concern because they do not break down via natural processes and are commonly described as persistent organic pollutants or "forever chemicals". They can also move through soils and contaminate drinking water sources and can build up (bioaccumulate) in fish and wildlife. Residues have been detected in humans and wildlife. Due to the large number of PFAS it is challenging to study and assess the potential human health and environmental risks; more research is necessary. According to the United States Environmental Protection Agency, exposure to some PFAS in the environment may be linked to harmful health effects in humans and animals. The International Agency for Research on Cancer (IARC) has classified PFOA as carcinogenic to humans and PFOS as possibly carcinogenic. According to the National Academies of Sciences, Engineering, and Medicine, PFAS exposure is linked to increased risk of dyslipidemia (abnormally high cholesterol), suboptimal antibody response, reduced infant and fetal growth, and higher rates of kidney cancer.
Health concerns related to PFASs have resulted in numerous litigations (see Timeline of events related to per- and polyfluoroalkyl substances). PFAS producers such as 3M, Chemours, DuPont and Corteva have reached billion dollar agreements to settle claims against them. The use of PFAS is regulated in several parts of the world, with some plans to phase them out entirely from products.