By Sarah C. P. Williams, Stanford News
They keep scrambled eggs from sticking to Teflon pans, takeout food from leaking out of its cardboard box, and raincoats from soaking through.
Per- and polyfluoroalkyl substances, a group of chemicals known as PFAS, have a powerful ability to repel oil and water and resist heat, making them useful in a wide range of consumer products and industrial applications.
Recent headlines about PFAS, however, are more likely to focus on their potential health risks; studies have shown that exposure to PFAS can decrease our immunity, and increase our risk of for certain types of cancer, birth defects, and liver and kidney disease. What’s more, PFAS can be hard to get rid of — often called “forever chemicals,” they stick around in the environment for decades and some may remain in our bodies for years.
Research is underway to figure out how exposure to different types and levels of PFAS impact health, but scientists already agree that there is cause for concern. In April, the Environmental Protection Agency finalized new limits on the levels of six PFAS in drinking water that, for the first time, require all public water systems to begin monitoring levels by 2027.
As research continues, some major retailers and manufacturers are voluntarily phasing out or banning PFAS, while others continue to use them. Meanwhile, consumers face uncertainty about how PFAS should factor in to their buying decisions — and even how to find out if products they use contain the chemicals.
Stanford Medicine scientists and clinicians who have studied PFAS say there are a few small steps that an average person can take to lower their personal exposure. Ultimately, they say, new government regulations will be key to lowering PFAS exposure and associated health outcomes.
The background
PFAS include more than 10,000 man-made substances that all have tight chemical bonds between their carbon and fluorine atoms. This incredibly tight bond — one of the strongest single bonds in chemistry — gives them their useful properties: They don’t let water seep through and they don’t break down when exposed to moderate heat. But their impenetrable nature also leads to their persistent presence in the environment.
Since the 1950s, PFAS have been commonly used in items including firefighting foam, paint, stain-resistant carpeting, cosmetics, cookware, pizza boxes, popcorn bags and clothing. Over the many decades, the ubiquitous use of PFAS by many industries has led to an accumulation of the chemicals in water, soil, wildlife and our bodies.
In the late 1990s and early 2000s, the EPA was first alerted to the presence of PFAS in the human body and the possible risks they have on health. Over the following years, lawsuits and investigative journalism revealed that chemical manufacturers that included DuPont and 3M had long hidden evidence of the health risks of being exposed to PFAS. Records and insider testimonials showed that as far back as the 1970s, industry scientists knew that PFAS exposure could lead to liver damage — and even death — in animals.
As a result, numerous lawsuits held the companies responsible for the cleanup of contaminated water supplies near manufacturing facilities. States including California have limited the use of PFAS in food packaging and proposed broader bans of the chemicals. A 2023 evaluation by the World Health Organization concluded that there was sufficient evidence to classify two of the most commonly used and detected PFAS — perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) — as carcinogenic and possibly carcinogenic to humans, respectively, because of their molecular effects and, for PFOA, possible link to kidney and testicular cancer.
“Once all these health studies started to come to light, independent scientists started doing more and more work on the effects of PFAS,” said Stanford Medicine’s Lisa Patel, MD, a clinical associate professor of pediatrics, who is on the executive committee for the American Academy of Pediatrics Council on Environmental Health and Climate Change. “Each new study that comes out concerns us more, not just because of what the health effects of these chemicals are, but because of how hard it is to get rid of them once they’re out there.”
What can be done?
Establishing new governmental regulations on chemicals like PFAS takes time — and lots of evidence. So far, most of the evidence on the health risks of PFAS come from people who live near manufacturing facilities and are exposed to high levels of PFAS in their drinking water. Experts are unsure what this means for people exposed to lower levels of the chemicals.
We have to do the best we can, which means looking at this data from communities that have had high exposure levels and extrapolating it to say, ‘Well, then it’s probably bad for all of us.’
Lisa Patel
“We have to do the best we can, which means looking at this data from communities that have had high exposure levels and extrapolating it to say, ‘Well, then it’s probably bad for all of us,'” explained Patel.
Studies looking at the long-term impacts of PFAS exposure must continue collecting data for decades, and gauging people’s exposures in these subsequent decades is difficult, she said. Moreover, finding people who haven’t been exposed to any PFAS chemicals for a control group for research is near-impossible; studies measuring PFAS levels in the blood of healthy volunteers have found that more than 95% of Americans have PFAS in their blood.
“There’s just a lot we don’t know,” said Brian Linde, MD, a clinical assistant professor of primary care and population health at Stanford Medicine and chief of occupational health at the U.S. Department of Veterans Affairs Palo Alto Health Care System. Linde was on the committee of expert scientists and clinicians who produced a 2022 National Academies report on PFAS exposure and testing.
“What makes these questions about PFAS so challenging is the sheer number of different PFAS chemicals and their widespread and persistent nature,” added Linde.
For many of the thousands of PFAS that exist, no single test exists to measure their levels in humans and no studies have analyzed their potential health effects; nearly all existing data revolves around PFOA, PFOS, and a few of the other most common PFAS chemicals. In addition, as companies phase out the use of some PFAS, they replace them with other chemicals designed to be water-repellant and heat-resistant. But studies on the health impacts of these chemicals are often lacking, too.
This leads to many questions and challenges surrounding what PFAS regulations might look like in the future.
What makes these questions about PFAS so challenging is the sheer number of different PFAS chemicals and their widespread and persistent nature.
Brian Linde
“There are thousands of these chemicals out there in the marketplace, and the vast majority of them have not been systematically studied,” said Stanford Medicine environmental epidemiologist Andres Cardenas, PhD, assistant professor of epidemiology and population health. “It would take forever to start creating policies and regulations for every single one, one at a time. So we need another path forward.”
What the science says
Cardenas has analyzed years of national health data to try to uncover how PFAS exposure changes people’s health. In 2019, he reported that higher levels of PFOA in the blood are associated with higher risk of diabetes. His other studies have found high PFAS exposure for pregnant women is associated with lower birth weight babies and altered immune function. Among all adults he has shown that higher blood PFAS levels are associated with lower kidney function, adverse lipid profiles and increases in body weight and size.
More recently, Cardenas launched a study to determine how fetal and early childhood PFAS exposure changes children’s immune systems and might make some vaccines work less well.
“With chemicals like PFAS, you can’t just carry out a randomized controlled trial where some people are exposed and some aren’t,” said Cardenas. “It takes a lot of observational data looking at people who are exposed at different levels and seeing what happens much later in life. It’s a lot of work.”
Cardenas and his colleagues also look at how PFAS impact cells and molecular markers. They’ve discovered that the chemicals, while they do not directly alter DNA, change when and where different genes are used in the body — called epigenetic regulation.
But Cardenas wonders how mixtures of PFAS might interact with each other — and with other environmental chemicals — to make the health impacts even more complex than his studies have captured so far.
“We often only look at a couple of chemicals at a time,” he said. “But if you’re exposed to many different PFAS, their impact on your health may multiply. This is an area that needs further research to truly protect public health from the complex chemical exposure we experience throughout our lives.”
We often only look at a couple of chemicals at a time. But if you’re exposed to many different PFAS, their impact on your health may multiply.
Andres Cardenas
Patel, who is currently working with the AAP on guidance surrounding chemicals of concern said the evidence for some health impacts is significant: High cholesterol levels, decreased immune response, thyroid and liver problems, and testicular and renal cancer are all associated with PFAS exposure.
Where does this leave us?
The science is clear that high levels of PFAS exposure can boost people’s risks of health problems. People who have been exposed to PFAS over many years, including people working in firefighting, chemical or manufacturing jobs, or people who live in areas with highly contaminated groundwater, should be aware of these risks and take steps to reduce their occupational exposure and other routes.
“But this is not just an occupational risk,” said Cardenas. “I think it’s a widespread public health concern because virtually everyone is exposed.”
Patel said there are some easy steps most consumers can to take to reduce their PFAS exposure, which include buying non-PFAS pots and pans, taking your own to-go containers with you when you eat out, and buying (and properly replacing) drinking water filters that can specifically filter PFAS chemicals.
But Cardenas, Patel and Linde all agree that these small, individual choices can only make a minor difference when there are so many routes to be exposed to PFAS; the chemicals can be contained in outdoor air, dust, and fresh produce and meat. The larger reduction in exposure will come when the chemicals are used less by manufacturers.
“It becomes very difficult to know if you’re really making a difference when you make these choices at the individual level,” said Cardenas. “But we know that policies reducing exposure levels at a national level are going to protect everyone.”
“This is not just an occupational risk. I think it’s a widespread public health concern because virtually everyone is exposed.
Andres Cardenas
“What the story of PFAS should teach us is that we can’t trust industry to have our health as their highest concern,” said Patel. “What the everyday citizen can do to make the largest impact is to support the EPA and to pressure our lawmakers to change the way we regulate chemicals in this country.”
Linde encourages people to seek out high-quality sources of information that balance the science with appropriate risk-reducing behavior.
“It’s important for people to look at the information that state and federal public health agencies are putting out because these are going to be the most credible sources of information,” he said.
