Per- and polyfluoroalkyl substances, known as PFAS, are described by the National Institute of Environmental Health Sciences (NIEHS) as a large, complex group of synthetic chemicals used in consumer products around the world since about the 1950s. The institute says human exposure is widespread but varies by geography and occupation. People are most likely exposed through water, food, products and air.
What PFAS are
According to NIEHS, PFAS molecules have a chain of linked carbon and fluorine atoms. The institute says the carbon-fluorine bond is one of the strongest, so these chemicals do not degrade easily in the environment.
The number of PFAS depends on the source. NIEHS cites a chemicals database kept by the U.S. Environmental Protection Agency (EPA) that lists nearly 15,000 of them. The National Institute for Occupational Safety and Health (NIOSH) says, on a page updated Oct. 28, 2026, that PFAS are a group of over 14,000 synthetic chemicals. NIOSH names PFOA, PFOS and “GenX” as examples of compounds in the group.
Where PFAS are used
NIEHS says PFAS are ingredients in many everyday products. They stop food from sticking to packaging or cookware, help clothes and carpets resist stains, and improve how well firefighting foam works. The institute adds that PFAS are used in the aerospace, automotive, construction and electronics industries.
NIOSH lists more uses, including stain-resistant textiles, food-handling materials, medical devices, paints, personal care products, construction materials and firefighting foam. NIEHS says PFAS are used in hundreds of products worldwide, which creates many chances for exposure.
How people are exposed
NIEHS says PFAS may leak into soil, water and air over time. People are most likely to be exposed through water or food that has been contaminated, through the use of products made with PFAS, or through breathing air containing PFAS. NIOSH gives a similar list for community exposure: air, consumer products, drinking water, food and soil.
Because PFAS break down slowly, if at all, NIEHS says people and animals are exposed again and again. Blood levels of some PFAS can build up over time. The institute describes bioaccumulation as a process in which people may take in more of the chemicals than they excrete.
NIEHS says one CDC report, using data from the National Health and Nutrition Examination Survey, found PFAS in the blood of 97% of Americans. It also says another report from that survey suggested blood levels of PFOS and PFOA fell after those chemicals were removed from consumer products in the early 2000s. Still, NIEHS says new PFAS chemicals have been created, and exposure to them is difficult to assess.
Who may be exposed more
NIOSH says workers can be exposed differently from the general public. They may touch concentrated products or breathe PFAS in the air at their workplace. A person’s industry, occupation and work activities can affect which PFAS they encounter, how much and how.
NIOSH says chemical manufacturing workers, firefighters and ski wax technicians are known to be exposed more than the general U.S. population. It notes that PFAS are often used in the foam used to fight liquid fuel fires.
The American Conference for Governmental Industrial Hygienists, a professional, not-for-profit scientific association, has set recommended limits for three PFAS in air. NIOSH says these Threshold Limit Values are not standards. They are health-based guidelines derived from scientific and toxicological information, based on an 8-hour workday and 40-hour workweek.
What research says about health effects
The Agency for Toxic Substances and Disease Registry (ATSDR) says research on how PFAS cause harm is ongoing. In a page dated July 22, 2025, it says epidemiological evidence suggests associations between increased exposure to specific PFAS and certain health effects. These include higher cholesterol levels, a lower antibody response to some vaccines, changes in liver enzymes, pregnancy-induced hypertension and preeclampsia, and small decreases in birth weight. For PFOA, ATSDR also lists kidney and testicular cancer.
ATSDR says the risk depends on exposure factors such as dose, frequency, route and duration. It also depends on individual factors such as sensitivity and disease burden, and on other determinants of health such as access to safe water and quality healthcare. NIEHS says the National Toxicology Program concluded that PFOA and PFOS suppressed the antibody response and were a hazard to immune system function in humans.
ATSDR says most animal studies tested PFAS at levels higher than the levels people experience from environmental exposure. Those studies found that PFAS can cause damage to the liver and the immune system in lab animals. ATSDR cautions that humans and animals react differently, so not all effects seen in animals may occur in humans.
NIEHS says there is still much to be learned. It says the many types of PFAS, which often occur in complex mixtures and in various everyday products, make them hard to study. ATSDR says scientists are still learning about the health effects of exposures to mixtures of different PFAS.