PFAS GUIDE
PFAS vs. PFOA vs. PFOS: What's the Difference?
Last updated: June 2, 2026
PFAS is the umbrella term for an entire class of thousands of chemicals. PFOA and PFOS are two individual chemicals within that class — the two most studied and most heavily litigated. In short: every PFOA and PFOS molecule is a PFAS, but most PFAS are neither PFOA nor PFOS.
For the broader picture, start with What Are PFAS (Forever Chemicals)? and What Does PFAS Stand For?
This page provides general educational information only and does not constitute medical or legal advice.
- PFAS is the class; PFOA and PFOS are two specific members of it.
- PFOA was tied to nonstick coating manufacturing; PFOS to stain repellents and firefighting foam.
- Both were largely phased out of U.S. production in the 2000s but persist and are still detected.
- Newer replacement chemistries such as GenX have raised their own concerns.
PFAS: The Umbrella
PFAS (per- and polyfluoroalkyl substances) covers thousands of chemicals that share a carbon-fluorine backbone. When coverage refers to "PFAS contamination," it usually means one or more specific compounds within that class were detected.
PFOA
PFOA — perfluorooctanoic acid, sometimes called C8 — is a single legacy PFAS historically associated with the manufacture of nonstick coatings and other products. It became central to early PFAS litigation involving drinking water contamination. U.S. producers phased it out through a voluntary stewardship program that ran through about 2015.
PFOS
PFOS — perfluorooctane sulfonate — is another single legacy PFAS used historically in stain- and water-repellent products and in aqueous film-forming foam (AFFF) used to fight fuel fires. Its main U.S. manufacturer began phasing it out in the early 2000s.
Legacy vs. Replacement PFAS
Because PFOA and PFOS were phased out, manufacturers introduced replacement chemistries such as GenX. The pattern is recurring: a compound is restricted, a substitute appears, and the substitute later draws its own scrutiny. This is part of why PFAS regulation tends to address the broader class rather than chasing one chemical at a time. Firefighting foam exposure is covered in AFFF Firefighting Foam Lawsuits.
Common Questions
Are PFOA and PFOS still used?
They were largely phased out of U.S. manufacturing in the 2000s, but because they persist they are still detected in water and blood testing today.
Why do PFOA and PFOS dominate the lawsuits?
They are the most studied PFAS, with the longest record of use and the most developed science linking them to health concerns, so they anchor much of the litigation. See PFAS Water Contamination Lawsuits.
