There is no single number that marks PFAS exposure as “dangerous,” but scientists and regulators have drawn several lines. Below 2 nanograms per milliliter (ng/mL) of total PFAS in your blood, adverse health effects are not expected. Above 20 ng/mL, the risk of health problems rises meaningfully. Between those two markers is a gray zone where risk increases gradually, and the specific PFAS compounds in your body matter.
Drinking Water Limits
The EPA finalized its first enforceable limits for PFAS in drinking water in 2024. For the two most studied compounds, PFOA and PFOS, the maximum contaminant level is 4 parts per trillion (ppt) each. Three other compounds, PFHxS, PFNA, and GenX chemicals, are capped at 10 ppt each. To put that in perspective, one part per trillion is roughly equivalent to a single drop of water in 20 Olympic-sized swimming pools. These limits are extremely low because PFAS build up in the body over time, so even tiny daily doses matter.
Public water systems have until 2029 to meet these standards. If your water comes from a private well, it is not covered by these regulations, and testing is your responsibility.
Blood Levels and Health Risks
The most direct way to gauge whether PFAS exposure has reached a concerning level is through a blood test. The National Academies of Sciences laid out a tiered framework based on the sum of several PFAS compounds in blood serum or plasma:
- Below 2 ng/mL (total PFAS): Health effects are not expected at this level.
- Between 2 and 20 ng/mL: Some risk exists, particularly for sensitive endpoints like immune function and cholesterol, but the evidence is less definitive.
- Above 20 ng/mL: There is an increased risk of adverse effects, including elevated LDL and total cholesterol and weakened vaccine response.
For individual compounds, German health authorities set action thresholds at 10 ng/mL for PFOA and 20 ng/mL for PFOS. At or above those levels, studies link exposure to higher cholesterol and reduced antibody production after vaccination. A study in German infants found that when the combined level of four PFAS compounds reached about 17.5 ng/mL in blood at one year of age, children produced fewer protective antibodies against diphtheria.
Liver effects have appeared in animal studies, but researchers have not yet pinpointed a specific blood concentration that reliably predicts liver damage in humans.
Why Small Amounts Build Up
PFAS are called “forever chemicals” because your body cannot break them down efficiently. PFOS has an average elimination half-life of about 5.4 years, meaning it takes that long for your blood level to drop by half, assuming no new exposure. PFOA clears a bit faster, with a half-life around 3.8 years. Some individuals eliminate these compounds much more slowly: in studies of former factory workers, PFOS half-lives ranged from about 2 to 22 years.
This slow clearance is the core reason regulators set drinking water limits in the single-digit parts per trillion. A dose that seems vanishingly small on any given day can accumulate over years and decades into a meaningful body burden.
Where Exposure Comes From
Contaminated drinking water is the biggest risk factor for high blood levels, but it is far from the only source. PFAS show up in food packaging, textiles, cookware, and even household dust.
Microwave popcorn bags are among the more concentrated consumer sources. Testing has found total PFAS levels up to 377 ng/g in popcorn bags from some manufacturers, and fast food wrappers can contain anywhere from trace amounts to several hundred nanograms per gram. Non-stick cookware leaches much smaller quantities, typically under 9 ng/g into food during cooking. Waterproof jackets and pants carry moderate levels (around 13 ng/g in consumer waterproof textiles), while flame-retardant fabrics tend to be higher. Children’s textile products sold in North America have been found with PFAS concentrations ranging from barely detectable to extraordinarily high levels, depending on the product and treatment.
The amount that actually migrates from a product into your body depends on contact time, temperature, and whether the material is wet or greasy. Greasy, hot food in direct contact with treated packaging transfers more PFAS than dry goods in the same wrapper.
How PFAS Affect Your Body
At elevated levels, PFAS interfere with several systems. The best-documented effect is raising cholesterol. People with higher blood PFAS consistently show increased LDL and total cholesterol, independent of diet and weight. This connection has been replicated across dozens of studies in different populations.
Immune suppression is the other well-supported concern. Children and adults with higher PFAS levels produce fewer antibodies after routine vaccinations, which can leave them less protected against infections. This is one reason regulators treat children’s exposure as especially important.
PFAS also disrupt hormone signaling. They interfere with the communication loop between the brain and thyroid gland, which can alter thyroid hormone levels. This disruption extends to other hormone-producing glands and has been linked in research to metabolic changes, including increased risk of weight gain during critical growth periods in children. Reproductive effects, including reduced fertility and pregnancy complications, have appeared in studies of highly exposed populations, though the dose-response relationship is less clearly defined than for cholesterol and immune effects.
Risks for Infants and Children
Infants can be exposed through breast milk and through water used to mix formula. PFAS have been detected in breast milk, but no studies have established a causal link between breast milk PFAS levels and a specific health effect in infants. There is also no established safe or unsafe threshold for PFAS in breast milk. Health agencies, including the Agency for Toxic Substances and Disease Registry, maintain that the benefits of breastfeeding outweigh the potential risks from PFAS. If you use powdered or concentrated formula, mixing it with filtered or tested water reduces one route of exposure.
Children are more vulnerable than adults partly because of their smaller body size (the same dose produces a higher blood concentration) and partly because their immune and endocrine systems are still developing. The diphtheria antibody study mentioned earlier found measurable immune effects in one-year-olds, reinforcing that early-life exposure carries distinct risks.
Reducing Your Exposure
Filtering your drinking water is the single most effective step. Granular activated carbon filters, the type found in many pitcher and under-sink systems, are expected to cost-effectively remove 76 to 87% of studied PFAS compounds. Reverse osmosis systems are generally considered even more effective, though specific removal rates vary by system and compound. If you are on a private well, testing your water first tells you whether filtration is necessary and helps you choose the right system.
Beyond water, practical steps include avoiding microwave popcorn bags and greasy fast food packaging when possible, choosing cookware that is not marketed as non-stick or that uses ceramic coatings, and selecting outdoor gear that is not treated with durable water repellents. None of these steps will eliminate exposure entirely, since PFAS are so widespread in the environment, but they can meaningfully reduce how much enters your body each day. Given how slowly these chemicals clear, even modest reductions in daily intake add up over years.