A new large-scale study published in the Journal of Occupational and Environmental Hygiene found that nearly all U.S. residents have so-called “forever chemicals” — PFAS — in their blood. In most cases, researchers detected not just one compound, but several at the same time.

Scientists analyzed more than 10,500 blood samples and found PFAS in 98.8% of them. Moreover, 98.5% of people had mixtures of different types of these substances in their bloodstream.

PFAS are a group of roughly 10,000 synthetic compounds that have been widely used in industry for decades. They can be found in everyday products such as nonstick cookware, stain-resistant clothing, packaging, electronics, cosmetics, and even medical equipment. These chemicals enter water, food, and the environment — and barely break down over time, which is why they are known as “forever chemicals.”

Their full impact on human health is still being studied, but some PFAS have already been linked to an increased risk of cancer, thyroid disorders, liver problems, elevated cholesterol levels, and weakened immune function.

The most commonly detected substance in the study was one type of PFAS found in nearly 98% of participants. It is already among the compounds facing restrictions in several countries because of potential health risks.

The authors of the study emphasize an important point: the issue is not just individual chemicals, but a constant “chemical cocktail” inside the body. Most people were found to carry multiple PFAS compounds simultaneously — often five or more.

According to the researchers, this is what raises the greatest concern. When these substances act together, their effects may intensify and impact multiple systems in the body at once, from the immune system to hormonal regulation.

Scientists refer to this as the “mixture effect” and argue that future research and safety regulations should take into account not only individual substances, but also their combinations.