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What research has found about PFAS, how scientists study them, and how to read PFAS findings without over- or under-stating them.

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Key findings

45%of U.S. tap water is estimated to contain at least one PFAS, from samples taken 2016 to 2021.Source: USGS, 2023
Nearly allpeople in the U.S. have PFAS in their blood.Source: ATSDR, NHANES
85% / 70%falls in blood PFOS and PFOA levels between 1999-2000 and 2018-2019.Source: ATSDR, NHANES
Group 1IARC classification of PFOA: carcinogenic to humans (December 2023).Source: IARC
4.0 pptEPA’s enforceable drinking water limit for PFOA, and for PFOS (April 2024).Source: EPA
Thousandsof PFAS exist, but most studies focus on a limited number of them.Source: EPA

Each finding is explained, with its caveats, on the linked topic pages: environment and drinking water, health and exposure and about PFAS.

Research topics

BiomonitoringNHANES has measured PFAS in the blood of the U.S. population since 1999.Health effectsStudies linking specific PFAS with cholesterol, vaccine response, birth weight and some cancers.Cancer evaluationIARC’s 2023 review of PFOA and PFOS.Clinical guidanceWhen blood testing is recommended and what the results mean.Drinking waterNational tap water sampling and EPA’s drinking water limits.Wildlife and foodHow PFAS build up in fish and seafood.TreatmentTechnologies that remove PFAS from water, and home filters.Replacement PFASNewer PFAS such as GenX chemicals and short-chain compounds.

How scientists study PFAS

  • Biomonitoring measures chemicals in people’s blood or urine. Since 1999, NHANES “has measured blood PFAS in the U.S. population.” [1]
  • Epidemiology compares health outcomes in groups of people with different levels of exposure. ATSDR’s list of PFAS health effects is based on this kind of evidence. [2]
  • Hazard evaluation weighs human, animal and mechanistic evidence together. IARC’s 2023 classification of PFOA drew on “sufficient evidence for cancer in experimental animals and strong mechanistic evidence” in exposed humans. [3]
  • Environmental monitoring measures PFAS in tap water, groundwater, fish and soil, as in the USGS national tap water study. [4]

How to read PFAS research

Association is not causation. ATSDR describes the evidence as suggesting “associations between increases in exposure to (specific) PFAS and certain health effects.” [2] An association means the two tend to occur together in studies; it does not by itself prove that one causes the other.

  • Which PFAS? Findings for PFOA or PFOS do not automatically apply to other PFAS. EPA notes that PFAS have “potentially varying effects and toxicity levels, yet most studies focus on a limited number of better known PFAS compounds.” [5]
  • What was measured? A study that tests for 32 PFAS, like the USGS tap water study, cannot rule out the others. [4]
  • Mixtures. People are usually exposed to several PFAS at once, and “scientists are still learning about the health effects of exposures to mixtures of different PFAS.” [2]
  • New evidence. ATSDR notes that “additional research may change our understanding of the relationship between exposure to PFAS and human health effects.” [2] Check the date of any source you rely on.

Where to go next

For definitions of the terms used on this site, see the glossary. For the original agency pages, see resources. For quick answers, see the FAQs.

Sources

  1. ATSDR, Fast Facts: PFAS in the U.S. Population, 12 November 2024.
  2. ATSDR, How PFAS Impacts Your Health, reviewed 22 July 2025.
  3. IARC, IARC Monographs evaluate the carcinogenicity of PFOA and PFOS, 1 December 2023.
  4. USGS, Tap water study detects PFAS ‘forever chemicals’ across the US, 5 July 2023.
  5. U.S. EPA, Our Current Understanding of the Human Health and Environmental Risks of PFAS, updated 14 July 2026.

Last reviewed: 29 September 2026.

Keep exploring

Health and ExposureNearly everyone in the U.S. has some PFAS in their blood. Here is how exposure happens, what studies have linked to certain PFAS, what blood tests can and cannot tell you, and practical steps to reduce exposure.GlossaryPlain-language definitions of the PFAS terms used on this site, with the source for each.ResourcesThe primary sources this site relies on, grouped by topic. Each link goes to the agency or organisation that published the information.