What Is PFAS? A Complete Guide to Forever Chemicals

What Are PFAS?

PFAS stands for per- and polyfluoroalkyl substances — a family of over 12,000 synthetic chemicals that have been manufactured and used in consumer and industrial products since the 1940s. They are built around one of the strongest bonds in organic chemistry: the carbon-fluorine bond. That bond makes them extraordinarily resistant to heat, water, oil, and biological degradation.

That resistance is exactly what makes them useful — and exactly what makes them dangerous.

Why Are They Called “Forever Chemicals”?

PFAS earned the name “forever chemicals” because they do not break down naturally in the environment. Unlike most organic pollutants, which decompose over months or years, PFAS persist for decades or longer in soil, water, and living tissue. Once they enter a water supply, they stay there unless actively removed through specialized filtration.

When you drink PFAS-contaminated water, these compounds accumulate in your body over time. The biological half-life of PFOS (one of the most studied PFAS compounds) in humans is estimated at 4 to 5 years — meaning it takes nearly half a decade for your body to eliminate just half of what you’ve absorbed.

Where Do PFAS Come From?

PFAS contamination enters drinking water from a wide range of sources:

• Industrial manufacturing — Facilities producing fluoropolymers (like Teflon and Gore-Tex) have historically discharged PFAS into waterways and groundwater.
• Aqueous film-forming foam (AFFF) — Firefighting foam used at military bases, airports, and training facilities is one of the largest sources of groundwater contamination. Hundreds of military sites across the U.S. have confirmed PFAS plumes. See our full guide to PFAS contamination near military bases.
• Wastewater treatment plants — Conventional treatment does not remove PFAS, so treated effluent carries these chemicals into rivers and lakes used as drinking water sources.
• Landfills — Consumer products containing PFAS (food packaging, stain-resistant fabrics, nonstick cookware) leach into groundwater as they degrade in landfills.
• Agricultural runoff — Biosolids (treated sewage sludge) applied as fertilizer can introduce PFAS to farmland, where rain carries them into local water supplies.

Which PFAS Are Regulated?

In April 2024, the EPA finalized the first-ever enforceable Maximum Contaminant Levels (MCLs) for six PFAS compounds under the Safe Drinking Water Act. Water systems must comply by 2029:

Compound	Full Name	MCL (ppt)
PFOA	Perfluorooctanoic acid	4
PFOS	Perfluorooctane sulfonic acid	4
HFPO-DA	GenX chemicals	10
PFHxS	Perfluorohexane sulfonic acid	10
PFNA	Perfluorononanoic acid	10
Hazard Index	Mixture of PFHxS, PFNA, HFPO-DA, PFBS	1 (unitless)

These limits are measured in parts per trillion (ppt) — extraordinarily low concentrations that reflect just how toxic these substances are considered to be at chronic exposure levels.

The EPA’s UCMR 5 program tested over 10,000 public water systems between 2023 and 2025 to establish a national baseline. You can look up your ZIP code on our homepage to see what was found in your area.

What Are the Health Concerns?

The scientific evidence linking PFAS exposure to health problems has grown substantially over the past two decades. Research has associated PFAS with:

• Cancer — Increased risk of kidney and testicular cancer, with emerging links to other cancers
• Thyroid disruption — Interference with thyroid hormone production and regulation
• Immune system suppression — Reduced vaccine effectiveness and increased susceptibility to infections
• Elevated cholesterol — Higher LDL cholesterol levels even at low exposure concentrations
• Reproductive effects — Reduced fertility, pregnancy complications, and lower birth weights
• Developmental effects in children — Potential impacts on growth, learning, and behavior

Children are particularly vulnerable because their bodies are still developing and they consume more water relative to their body weight than adults. For a deeper look at the health evidence, see our article on how PFAS affects your health.

What Can You Do?

The most effective steps you can take right now:

1. Check your water — Enter your ZIP code to see whether PFAS has been detected in your local water systems using real EPA testing data.
2. Install an effective filter — Not all water filters remove PFAS. Reverse osmosis and activated carbon systems with NSF 53 or NSF 58 certification are the most reliable options. See our guide to removing PFAS from your water and our filter reviews for specific recommendations.
3. Reduce other exposures — Avoid nonstick cookware, stain-resistant treatments, and microwave popcorn bags when possible. These won’t affect your water, but they reduce your total PFAS burden.
4. Stay informed — EPA regulations are still evolving. Follow our regulatory updates to understand what your water utility is required to do and by when.

PFAS contamination is widespread but not hopeless. Knowing what’s in your water is the first step toward protecting yourself and your family. Check your water now — it takes less than 10 seconds.