Understanding PFAS
A plain-language primer on the "forever chemicals", what they are, the types, where they're found, what the science says about health, and how they're regulated. Every fact links to an authoritative source.
1 · What PFAS are
PFAS, per- and polyfluoroalkyl substances, are a large family of thousands of synthetic chemicals that share a fluorinated carbon backbone. Every PFAS contains carbon–fluorine bonds, among the strongest in organic chemistry. That bond makes them repel water, grease, and heat, and makes them extraordinarily resistant to breakdown, so they persist in the environment and the body. Hence the nickname "forever chemicals." EPA ↗ ATSDR ↗
PFAS chemistry dates to the late 1930s–1940s (PTFE/Teflon was discovered in 1938; 3M began making fluorochemicals in the 1940s–50s; AFFF firefighting foam was co-developed with the U.S. Navy in the 1960s). Exact dates vary by source and are approximate.
How many are there? There is no single official total, it depends on the definition. EPA's regulatory inventory lists about 1,462 PFAS (770 in active U.S. commerce); a 2018 OECD global survey identified 4,730; EPA's research "master list" tracks a still-larger, growing universe. EPA TSCA ↗ OECD ↗
They're nearly everywhere: the CDC detects at least one PFAS in the blood of essentially everyone tested in the U.S. (though legacy PFOS/PFOA levels have fallen 70–85% since 1999), and the USGS estimates at least 45% of U.S. tap water contains one or more PFAS. ATSDR/CDC ↗ USGS ↗
2 · The types
"PFAS" isn't one chemical, it's a family. The key distinctions:
The most common individual compounds
- PFOA (8 carbons), used to make Teflon and coatings. Phased out of U.S. production.
- PFOS (8 carbons), used in Scotchgard, plating, and AFFF foam. Phased out (3M ended production 2000–02).
- PFHxS (6 carbons), stain/water treatments and foams; common in blood.
- PFNA (9 carbons), a fluoropolymer processing aid.
- GenX (HFPO-DA). EPA-described replacement for PFOA; still in use.
- PFBS (4 carbons), short-chain replacement for PFOS; still in use.
Long-chain vs. short-chain
Long-chain PFAS (carboxylic acids with 8+ carbons, sulfonic acids with 6+) like PFOA and PFOS were the first phased out. Short-chain replacements (e.g., PFBS) bioaccumulate less but are more mobile in water and equally persistent. EPA ↗ ITRC ↗
Polymer vs. non-polymer
Small non-polymer PFAS (PFOA, PFOS, etc.) are mobile and can enter the bloodstream, these dominate water contamination. Large fluoropolymers like PTFE (Teflon), PVDF, and FEP are generally too big to be bioavailable, but they have historically been made using non-polymer aids like PFOA or GenX, so an inert end product doesn't mean a PFAS-free supply chain. ITRC ↗
Precursors
Partially fluorinated PFAS that aren't the final product but degrade intostable PFOA/PFOS over time, a hidden reservoir that keeps regenerating the legacy compounds. USGS ↗
"Phased out" means major U.S. manufacturers stopped making PFOA/PFOS, voluntary stewardship, not outright bans. They still enter via imports, persist as legacy contamination, and form from precursor breakdown.
3 · Where PFAS is found
PFAS show up in products most people use without knowing it:
- Nonstick cookware (PTFE/Teflon)
- Grease-resistant food packaging, wrappers, popcorn bags, takeout boxes
- Stain/water-resistant carpet, upholstery, clothing
- Waterproof outdoor gear
- Some cosmetics & personal care; dental floss
- Ski & sport wax
- Certain cleaning products
- Firefighting foam (AFFF)
Major industrial uses include chrome/metal plating, semiconductor manufacturing, aerospace, automotive, and oil & gas. EPA ↗ ITRC ↗
In February 2024 the FDA announced that grease-proofing agents containing certain PFAS are no longer sold for food-contact use in the U.S., removing a primary dietary source. It applies to new sales, not products already in circulation or imports. FDA ↗
4 · Health effects
ATSDR lists studied associations: increased cholesterol; reduced antibody/vaccine response (notably in children); changes in liver enzymes; pregnancy-induced hypertension/preeclampsia; small decreases in birth weight; thyroid effects; and kidney and testicular cancer. ATSDR ↗
The independent, court-appointed C8 Science Panel (DuPont/Parkersburg WV litigation) found a "probable link" between PFOA and exactly six conditions: high cholesterol, ulcerative colitis, thyroid disease, testicular cancer, kidney cancer, and pregnancy-induced hypertension. "Probable link" was a legal "more likely than not" standard in one heavily-exposed community. C8 Panel ↗
In 2023 the WHO's IARC classified PFOA as "carcinogenic to humans" (Group 1) and PFOS as "possibly carcinogenic" (Group 2B). Important nuance: IARC Group 1 is a hazard identification (can it cause cancer under some conditions?), not a risk statement. PFOA's classification rests on strong animal and mechanistic evidence, with the human cancer epidemiology itself rated only "limited." IARC ↗
5 · U.S. regulations
On April 10, 2024, EPA finalized the first federal, legally enforceable PFAS drinking-water standards (Maximum Contaminant Levels, in parts per trillion):
Separately, in 2024 EPA designated PFOA and PFOS as hazardous substances under CERCLA (the Comprehensive Environmental Response, Compensation, and Liability Act, or Superfund), triggering release reporting and letting EPA compel polluters to fund cleanups. This is final and in effect. EPA CERCLA ↗
States have moved independently, about a dozen set their own drinking-water limits (some stricter than federal), and a fast-growing number ban PFAS in products (Maine 2030 phase-out, Minnesota's "Amara's Law" through 2032, plus cookware/packaging/textile/foam bans elsewhere). Harvard EELP tracker ↗