What Are PFAS (Forever Chemicals)?

What Does PFAS Stand For?

PFAS stands for per- and polyfluoroalkyl substances. The term covers a large family — by some counts more than 12,000 — of synthetic chemicals built around chains of carbon atoms bonded to fluorine atoms. Because PFAS describes a whole class rather than one chemical, two products can both “contain PFAS” while involving very different specific compounds.

For a deeper breakdown of the terminology, see What Does PFAS Stand For?

Why Are PFAS Called “Forever Chemicals”?

The carbon-fluorine bond at the core of every PFAS molecule is one of the strongest single bonds in organic chemistry. That strength is exactly what makes PFAS useful — they shrug off heat, water, and grease — but it also means they do not readily break down in nature or in the body. Instead, they can accumulate in soil, groundwater, drinking water, wildlife, and people over time. That persistence is the reason for the “forever chemicals” nickname.

PFAS vs. PFOA vs. PFOS

These three terms are often used interchangeably in news coverage, but they are not the same thing:

• PFAS is the umbrella term for the entire class of per- and polyfluoroalkyl substances.
• PFOA (perfluorooctanoic acid) is a single, heavily studied PFAS once used to make nonstick coatings and other products.
• PFOS (perfluorooctane sulfonate) is another single, well-studied PFAS historically used in stain repellents and firefighting foam.

PFOA and PFOS are sometimes called “legacy” PFAS. U.S. manufacturers largely phased them out beginning in the early 2000s and replaced them with newer compounds such as GenX. Because the legacy chemicals persist, they are still detected in water and in blood testing today. For a fuller comparison, see PFAS vs. PFOA vs. PFOS Explained.

Where PFAS Are Found

PFAS have been used in a wide range of industrial processes and everyday products, including:

• Nonstick cookware coatings
• Stain- and water-resistant fabrics, carpets, and upholstery
• Grease-resistant food packaging and wrappers
• Certain cosmetics and personal care products
• Aqueous film-forming foam (AFFF) used to fight fuel fires
• A variety of manufacturing and industrial applications

Firefighting foam in particular is a major PFAS topic because of heavy use at airports and military installations. See AFFF Firefighting Foam Lawsuits.

How People Are Exposed to PFAS

The exposure route discussed most often is contaminated drinking water, especially in communities near military bases, airports, landfills, or industrial sites. The U.S. Geological Survey has estimated that a significant share of the nation’s tap water contains at least one type of PFAS. People may also encounter PFAS through some food and food packaging, certain consumer products, household dust, and some occupational settings.

For more on exposure pathways, see How Do PFAS Get Into the Body?

How Long Do PFAS Stay in the Body?

Many PFAS leave the body slowly. Researchers describe the time it takes the body to clear half of certain PFAS compounds in terms of years rather than days or weeks, which is why repeated low-level exposure can lead to measurable buildup over time. The exact timeline varies considerably by compound. For more detail, see How Long Do PFAS Stay in the Body?

Are PFAS Dangerous to Humans?

Scientific and public-health reviews have associated some PFAS with a range of health concerns. Commonly cited associations include certain cancers (such as kidney and testicular cancer), thyroid disease, elevated cholesterol, changes in liver enzymes, immune effects including reduced response to vaccines, and pregnancy-related concerns such as high blood pressure and lower birth weight. These are associations drawn from population studies; research is ongoing, and any effect can depend on the specific PFAS compound, the dose, and how long exposure lasted.

For the conditions most often researched in connection with PFAS, see Are PFAS Dangerous to Humans?, PFAS Health Effects, PFAS and Kidney Cancer, PFAS and Testicular Cancer, PFAS and Thyroid Disease, and PFAS and Ulcerative Colitis.

Why PFAS Are Connected to Lawsuits

Because PFAS are persistent, widely used, and linked in studies to health concerns, they have produced one of the largest waves of environmental and product-liability litigation in the country. These cases generally allege that manufacturers or operators contaminated water supplies and did not adequately warn the public about the risks.

PFAS litigation is not a single lawsuit. It includes public water system claims brought by utilities and cities, individual injury claims, state environmental actions, and firefighting foam claims. For the litigation-focused overview, see PFAS Water Contamination Lawsuits and the regularly updated PFAS Water Contamination Lawsuit Update.

Filing deadlines vary by state and are often shorter than people expect. See PFAS Lawsuit Statute of Limitations by State.

How PFAS Are Regulated

PFAS regulation has been changing quickly. In 2024, the U.S. Environmental Protection Agency finalized the first national drinking water limits for several PFAS compounds, including PFOA and PFOS. Those standards have since been the subject of legal challenges and regulatory reconsideration, and the rules governing testing, reporting, and cleanup continue to evolve at both the federal and state levels.

For analysis of how shifting federal PFAS rules intersect with compliance and litigation, see What EPA PFAS Rule Changes May Mean for Regulated Entities and Litigation.

Common Questions People Ask

What does PFAS stand for?

PFAS stands for per- and polyfluoroalkyl substances. It is not one chemical but a class of thousands of synthetic chemicals that share a chain of carbon and fluorine atoms. Learn more →

Why are PFAS called “forever chemicals”?

The carbon-fluorine bond in PFAS is one of the strongest in chemistry, so these chemicals resist breaking down. They can persist for a very long time in soil, water, and the human body.

What is the difference between PFAS, PFOA, and PFOS?

PFAS is the umbrella term for the whole class. PFOA and PFOS are two specific, well-studied PFAS that were widely used for decades and largely phased out of U.S. manufacturing, though they remain detectable. Learn more →

Are PFAS harmful to human health?

Scientific reviews have associated some PFAS with certain cancers, thyroid disease, high cholesterol, immune effects, and pregnancy-related concerns. Research is ongoing. Learn more →

How are people exposed to PFAS?

The most common route discussed is contaminated drinking water. People may also be exposed through some food and food packaging, consumer products, household dust, and some workplaces. Learn more →