What are PFAS, or "forever chemicals"?
PFAS — per- and polyfluoroalkyl substances — are a family of thousands of synthetic chemicals defined by carbon-fluorine bonds, among the strongest in organic chemistry. That bond strength is exactly why they are useful and why they are a problem.
Why they are used. PFAS repel water, oil and grease, resist heat, and reduce friction. That makes them valuable in non-stick cookware, waterproof and stain-resistant fabrics, grease-proof food packaging, firefighting foams, cosmetics, medical devices, and semiconductor and aerospace manufacturing.
Why "forever chemicals". The carbon-fluorine bond is so stable that PFAS do not meaningfully break down in the environment on human timescales. They are highly mobile in water, persist in soil and groundwater, and bioaccumulate. They have been detected in rainwater globally, in Arctic wildlife, in drinking water supplies across many countries, and in the blood of the overwhelming majority of people tested.
What is known about health effects. Evidence is strongest for the older, longer-chain compounds PFOA and PFOS, both now restricted internationally. Associations reported in epidemiological studies include raised cholesterol, liver enzyme changes, reduced vaccine response in children, thyroid disease, pregnancy-induced hypertension, lower birth weight, and kidney and testicular cancer. The US National Academies has published guidance on clinical follow-up for exposed individuals.
The honest position is that associations are established for some compounds, causation is clearer for some outcomes than others, and the thousands of newer replacement compounds are far less studied — which is itself a significant concern, since substitution has repeatedly moved to chemically similar alternatives.
Regulation is tightening. The EU has proposed a broad restriction on the whole class, the US EPA has set enforceable drinking water limits for several compounds, and litigation has produced very large settlements.
Reducing exposure: filtered water where supplies are affected, avoiding grease-proof food packaging, and checking treatments on textiles and cookware.