What Are PFAS? The Forever Chemicals Explained (2026 Guide)

What Does PFAS Stand For?

PFAS stands for Per- and Polyfluoroalkyl Substances. The name is a chemistry label, not a brand. It describes a family of more than 12,000 different synthetic compounds, according to the EPA . What ties them all together is a chain of carbon atoms with fluorine atoms bonded to them.

That carbon-fluorine bond matters. It is the strongest single bond in organic chemistry. It does not break down under heat, water, sunlight, or most natural processes. That is the entire reason these chemicals were useful in the first place. Non-stick coatings, water-repellent fabrics, stain-resistant carpets, and firefighting foam all rely on PFAS because the bond will not give up.

The same property that made PFAS useful is what makes them a problem now. Once they enter soil, water, or a human body, they tend to stay.

Within the PFAS class, chemists draw a line between two sub-groups. Perfluoroalkyl substances have every available carbon site bonded to fluorine. Polyfluoroalkyl substances have most but not all sites bonded to fluorine, with some carbon-hydrogen bonds left. Polyfluoroalkyl PFAS can degrade in the environment over time, but the breakdown products are usually perfluoroalkyl compounds. In other words, partial PFAS often turn into more persistent PFAS rather than going away.

That detail matters when you read marketing claims. A company that says its product is "made with degradable PFAS" may be technically accurate, while the degradation product sitting in your water is exactly the kind of forever chemical the EPA now regulates.

Why Are PFAS Called "Forever Chemicals"?

The phrase forever chemicals was coined by Joseph Allen of Harvard T.H. Chan School of Public Health in a 2018 Washington Post op-ed. The nickname stuck because it is accurate. PFAS do not biodegrade in any meaningful timeframe.

The CDC ATSDR Toxicological Profile for Perfluoroalkyls reports human serum half-lives of roughly 2 to 4 years for PFOA and around 5 years for PFOS. Some newer compounds clear faster, but most persist for years. For comparison, alcohol has a half-life of around 5 hours.

In soil and water the timeline stretches further. PFAS released into a river in the 1980s can still be detected downstream today. There is no microbe, no enzyme, no temperature in normal industrial use that fully destroys them. Incineration above 1,000 degrees Celsius can break the carbon-fluorine bond, but most municipal incinerators run cooler than that and may release PFAS into the air instead.

The persistence has practical consequences. A 2021 study by the Environmental Working Group estimated that PFAS levels in US drinking water from contaminated sites would take decades to drop on their own, even if all current sources stopped today. Cleanup methods are still experimental for most utilities. Granular activated carbon and ion exchange resins can pull PFAS out of water at the treatment plant, but the spent media then has to be disposed of as PFAS waste, which means landfill or high-temperature incineration. The chemicals do not disappear, they move.

That is also why filtration at the tap has become a primary defense for households. If the chemicals will be in the water supply for the next 30 years, the most reliable way to drink less of them is to remove them yourself. The right filter depends on whether you rent or own, your budget, and whether you want only drinking water filtered or every tap in the house.

The Most Common PFAS Compounds

Of the 12,000 PFAS compounds, six are regulated by the EPA under the April 2024 final rule. Here is what each one is, where it came from, and the legal limit in your drinking water.

ppt = parts per trillion. HI = Hazard Index, a mixture calculation. Source: EPA PFAS National Primary Drinking Water Regulation (April 10, 2024).

Where Do PFAS Come From?

PFAS have been in use since DuPont and 3M started producing them in the 1940s. Over eight decades they spread into nearly every part of consumer and industrial life. The NIH National Institute of Environmental Health Sciences groups the main sources into four buckets.

The USGS National Water-Quality Assessment tested tap water at 716 locations across the US in 2023. PFAS was detected in at least 45 percent of samples. The number was higher in urban areas and in regions near military installations.

Health Effects of PFAS

The strongest evidence for PFAS health effects in humans comes from the C8 Science Panel, a court-ordered study of around 69,000 people in the Mid-Ohio River Valley who were exposed to PFOA from a DuPont plant. Steenland and colleagues reviewed the panel data in Environmental Research (2018) and identified probable links to six conditions:

• Kidney cancer
• Testicular cancer
• Thyroid disease
• Ulcerative colitis
• High cholesterol
• Pregnancy-induced hypertension

The CDC ATSDR PFAS Health Effects page adds reduced vaccine response in children, low infant birth weight, and changes in liver enzymes. The National Toxicology Program classifies PFOA and PFOS as "presumed to be an immune hazard to humans" based on reduced antibody response to vaccines.

CDC biomonitoring data published by Calafat and colleagues in the National Report on Human Exposure to Environmental Chemicals found detectable PFAS in 98 percent of blood samples from the US population. Median levels have dropped since 2000, when PFOS and PFOA were phased out, but they remain present in nearly everyone.

Important note on language: the studies above show that PFAS exposure is linked to these conditions, meaning the statistical association is strong and consistent. They do not prove that PFAS causes the conditions in a given person. Randomized controlled trials of PFAS exposure in humans do not exist for ethical reasons. If you are worried about your own exposure, speak to your doctor.

A note on children and pregnancy. The CDC and the American College of Obstetricians and Gynecologists both flag prenatal and early childhood PFAS exposure as a higher concern than adult exposure. Developing immune and endocrine systems are more sensitive, and infants can receive PFAS through breastmilk if the parent has elevated levels. The benefits of breastfeeding still outweigh PFAS concerns according to current CDC guidance, but it is worth raising with a pediatrician if a water test comes back high.

What about lowering body levels? Once PFAS are in your blood, the body clears them slowly through bile and urine. A 2022 randomized trial in Australian firefighters (Gasiorowski et al., JAMA Network Open) found that blood donation every 12 weeks for a year lowered serum PFOS by 30 percent on average. Plasma donation worked even better. The trial is small and applies to occupationally exposed adults, not the general population, but it is one of the few interventions with measurable effect. Talk to your doctor before changing anything based on this.

The EPA's 2024 Drinking Water Rule

On April 10, 2024 the EPA finalized the first national drinking water standards for PFAS. It was the biggest update to the Safe Drinking Water Act in decades. The rule sets enforceable Maximum Contaminant Levels (MCLs) for six PFAS compounds:

• PFOA: 4 parts per trillion
• PFOS: 4 parts per trillion
• PFHxS: 10 parts per trillion
• PFNA: 10 parts per trillion
• GenX (HFPO-DA): 10 parts per trillion
• PFBS: regulated as part of a Hazard Index mixture calculation

The rule also sets non-enforceable health goals (MCLGs) of zero for PFOA and PFOS, which is the EPA's way of saying no level of exposure is considered safe. Public water systems have until 2027 to complete initial monitoring and until 2029 to comply with the limits and notify customers if their water exceeds them.

A part per trillion is a tiny unit. One ppt is roughly one drop of water in 20 Olympic-sized swimming pools. The fact that the EPA set the limit at 4 ppt reflects how toxic these compounds are believed to be at low doses, not how easy they are to measure.

What the rule changed in practice. Before April 2024, the EPA only had non-binding health advisories for PFOA and PFOS, set at 70 ppt in 2016 and lowered to near-zero advisories in 2022. Utilities could ignore the advisories without legal consequence. The 2024 rule turns those numbers into enforceable limits with monitoring, reporting, and public notification requirements. Water systems that exceed an MCL have to install treatment or find an alternative water source, and they have to tell their customers. That last part is what changes the experience for households on municipal water.

Who is covered. The rule applies to all 66,000 community water systems serving year-round residents and to non-transient non-community systems like schools and workplaces with their own wells. Private wells are not covered. If you draw water from your own well, the EPA limits give you a useful target number, but no one is required to test for you. That is the responsibility of the property owner.

Read the full rule on the EPA PFAS National Primary Drinking Water Regulation page . For a plain-English walkthrough of what the rule means for your tap, see our EPA PFAS rule 2027 explainer.

How to Test Your Water for PFAS

You cannot taste, smell, or see PFAS. The only way to know what is in your water is to test for it. Three reliable options:

1. EWG Tap Water Database (free). Enter your zip code at ewg.org/tapwater. You get a utility-level overview based on public water reports. It is a starting point, not a substitute for a personal test.
2. Mail-in lab test ($299 range). Tap Score and SimpleLab both offer PFAS-specific panels that test for 30 or more compounds. You collect a sample, mail it in, and get results in 2 to 3 weeks. See our PFAS test cost guide for a full breakdown.
3. EPA Consumer Confidence Report. If you are on municipal water, your utility must publish an annual water quality report by July 1. Most utilities post it online. PFAS testing data became mandatory under the 2024 rule, with full reporting expected by 2027.

At-home test strips and TDS meters do not detect PFAS. The molecules are too small and chemically inert for those tools. Anyone selling a $20 strip that "detects forever chemicals" is selling something that does not work. The lab tests above use mass spectrometry, which costs more than a kitchen-table device can match.

If you draw from a private well, testing is especially important because no utility report covers you. Wells near military bases, airports, industrial sites, or farm fields with biosolids history sit at higher risk. The EPA recommends testing every 1 to 3 years for any contaminant of concern, including PFAS if known sources are nearby. See our guide on how often to test well water for a schedule based on your situation.

For a step-by-step look at what to do if a test comes back positive, read what to do after a positive PFAS test.

For Context: The Scale of the PFAS Problem

A few numbers help frame how widespread this is.

• In June 2023, 3M agreed to pay up to $12.5 billion to US public water systems to settle PFAS contamination claims. DuPont, Chemours, and Corteva agreed to a separate $1.185 billion settlement the same month.
• The EPA has identified more than 14,000 sites in the US with confirmed or suspected PFAS contamination, based on data tracked by the Environmental Working Group.
• The Department of Defense has flagged over 700 military installations for PFAS investigation due to historical AFFF use.
• According to the National Toxicology Program , PFOA and PFOS are presumed human immune hazards based on consistent evidence from animal and human studies.

The scale of the cleanup effort is one reason the EPA chose a class-based approach rather than regulating each of the 12,000 compounds separately. The 2024 rule starts with six. More are expected to follow.

States are also moving faster than the federal government in some cases. As of 2026, more than a dozen states have set their own PFAS limits for drinking water, surface water, or soil, with some thresholds tighter than the EPA's. Michigan, New Jersey, New Hampshire, and Vermont were among the first. The result is a patchwork of rules where a chemical legal in one state's groundwater is banned in a neighbor's, and where utility responsibilities vary by zip code.

For a state-by-state breakdown of testing results and known contamination sites, see our PFAS contamination by state map.

Frequently Asked Questions

References

1. EPA. Our Current Understanding of the Human Health and Environmental Risks of PFAS.
2. EPA, April 10, 2024. PFAS National Primary Drinking Water Regulation.
3. CDC Agency for Toxic Substances and Disease Registry. Toxicological Profile for Perfluoroalkyls.
4. NIH National Institute of Environmental Health Sciences. Perfluorinated Chemicals (PFCs).
5. USGS, 2023. Tap Water Study Detects PFAS Forever Chemicals Across the US.
6. National Toxicology Program (NIH). Per- and Polyfluoroalkyl Substances Research.
7. Steenland K, et al. (2018). A review of the epidemiologic literature on PFOA exposure. Environmental Research.
8. Sunderland EM, et al. (2019). A review of the pathways of human exposure to PFAS. Environmental Science & Technology Letters.
9. Calafat AM, et al. CDC National Report on Human Exposure to Environmental Chemicals.