How worried should we be about PFAS, the 'forever chemicals'?

New research on "forever chemicals" called PFAS has added to growing concerns about their potential effects on human health.

PFAS, or perfluoroalkyl and polyfluoroalkyl substances, are chemicals used in many household products. We've known for years that they can enter our bodies through the food and water we consume. But recently, scientists showed for the first time that some PFAS can be absorbed through the skin and into the bloodstream.

Previously, skin was thought to act as a barrier against PFAS, which have been tied to a range of concerning health effects. Many everyday items our skin touches, including makeup and fabrics, can contain these chemicals.

So, what do we know about the effects of PFAS on our health?

Related: PFAS 'forever chemicals' to officially be removed from food packaging, FDA says

How do PFAS get in the body?

PFAS are human-made chemicals that have been used since the 1940s and are still found in many products, including nonstick cookware, waterproof clothing, cosmetics and dental floss. They are largely prized for being nonstick; repellent to water, oils and stains; and flame retardant. They are sometimes added to products to improve their texture or shine.

Current estimates suggest that nearly 15,000 different PFAS have been invented, and more continue to be developed.

PFAS take thousands of years to break down and thus accumulate in the environment and in humans' and animals' bodies. They are found in soil, food, air and drinking water, as well as in the blood of most people in the U.S. 

One way they enter human blood may be through the skin, recent research suggests. Published in May in the journal Environmental International, the study measured the absorption of 17 commonly used PFAS using 3D models made from lab-grown human skin. 

"We found that most of the PFAS we included in our study can absorb into human skin," Oddný Ragnarsdóttir, who led the study as part of her doctorate at the University of Birmingham in the U.K., told Live Science. At this point, though, it's unclear what doses of PFAS people would realistically be exposed to via skin contact, and how harmful those doses are.

PFAS have also been found in breast milk, and more than 40 studies have found them in cord blood collected at birth. Recent research, published in May in the journal Eco-Environment & Health, showed that PFAS readily travel across the placenta. This backs evidence that many people may first be exposed to PFAS before birth.

Related: Scientists find a simple way to destroy 'forever chemicals'

What do PFAS do to the body?

Once in the bloodstream, PFAS bind to proteins and can enter cells and organs, where they remain for years or even decades. Scientists are still learning about the health effects of different PFAS, but there's some evidence of their potential harms.

In 2016, the National Toxicology Program published a review about the two most common PFAS: perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). The review primarily considered experiments in lab animals and epidemiological studies in people, which looked for links between PFAS exposure and health effects at a population level. 

It concluded that both PFOA and PFOS are likely "immune hazards to humans." The strongest evidence suggests both PFOA and PFOS can hinder antibody responses. Weaker evidence linked PFOA to a higher risk of autoimmune disease and allergies in humans, while in animals, PFOS suppress natural killer cells, which normally destroy diseased cells, including cancer. 

What is less clear, the review noted, is exactly how PFOA and PFOS produce these effects. 

More recent studies have started to unravel this, finding that PFAS can alter the function of various proteins that are either made by the body or obtained through diet. In addition, a 2023 review by the World Health Organization's International Agency for Research on Cancer (IARC) found "strong mechanistic evidence" linking PFOA and PFOS to epigenetic changes, meaning molecular changes that affect how genes are activated. For PFOA, there was also "sufficient" evidence of the chemical being able to cause cancer in lab animals, while similar evidence was "limited" for PFOS. 

As a result, in 2023, the IARC classified PFOA as "carcinogenic to humans" and PFOS as "possibly carcinogenic to humans." The agency's classifications aren't related to how much a substance might increase cancer risk but rather how conclusively the IARC can say it causes cancer at all. In that respect, the evidence is stronger for PFOA than for PFOS.

Related: More than 50 new environmental chemicals detected in people

Studies also suggest that PFAS might affect reproductive health. A 2021 review found that exposure to PFOA and PFOS were both associated with lower testosterone levels and semen quality in men, at a population level.

Exposure to PFAS in the womb has also been linked to lower antibody responses to childhood vaccines, such as those for diphtheria, rubella and mumps. This early exposure is also linked to changes in how teens and young adults break down fats and proteins; there's concern that this might raise the risk of metabolic diseases. 

Beyond PFOA and PFOS, thousands of other PFAS are yet to be studied. One big thing we don't know yet is which PFAS are in which products and at what concentrations, said Stuart Harrad, a professor of environmental chemistry at the University of Birmingham and senior author of the recent study on PFAS skin absorption. 

"If a PFAS that is well absorbed is present in high concentrations in a cosmetic or fabric with which we have prolonged skin contact," Harrad said, "then the resultant exposure will be substantial and may be on a par with what we receive via our diet or drinking water."  

With precise measurements of the doses people are exposed to through the skin, toxicologists and epidemiologists could begin to evaluate the health effects of those doses, he said.

What now?

PFOS and PFOA have steadily been phased out of U.S. production since the early 2000s. This has resulted in their decline in blood levels over the past two decades, but the chemicals persist in the environment and are still used in other countries. In addition, new, less-studied PFAS have arisen to replace those two. 

"As 'old' PFAS are phased out or banned, 'new' ones have been introduced," said Andrew Watterson, a public health researcher at the University of Stirling in Scotland. 

"The cumulative and total risks to workers making, applying and exposed to many PFAS, and to consumers and the public who come into contact with PFAS and the wider environment, have still not been fully assessed," he told Live Science in an email. "The data gaps that still exist for chemicals that have been used for decades are very worrying."

Federal agencies and states are making efforts to limit PFAS in water and consumer products. However, removing PFAS from our bodies and the environment will be difficult and costly. 

In the meantime, the Environmental Protection Agency has released an updated guide on how consumers can reduce their PFAS exposure. It advises people to install in-house water filters; to avoid eating fish from contaminated waterways; and to avoid PFAS-treated fabrics and other household products known to contain PFAS.

Consumers may be able to pressure manufacturers to remove or reduce PFAS in their products, Watterson said. But in general, there is little the public can do to avoid contact with chemicals already present in the environment, he said. Solutions will require regulating all PFAS, he said, and ultimately cutting them off at their sources.

This article is for informational purposes only and is not meant to offer medical advice.

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!