Next time you pick up a pizza from your favorite pizzeria and toss the box in your front seat, think about why the grease doesn’t saturate through the cardboard onto your upholstery. Or when you hear popcorn bursting in a bag in your microwave, consider why the oil doesn’t ooze out and the paper doesn’t burst into flames, even when some kernels turn black.

The answer is likely to be PFAS. Per- and polyfluoroalkyl substances are a group of about 4,700 chemicals that make carpets and upholstery stain-resistant and help firefighters douse burning oil and gas. Some PFAS versions keep your burger from sticking to its fast-food wrapper and your salad from turning its fiber-based bowl into a soggy mess.

For years, scientists and environmental advocates have been sounding the alarm about these persistent “forever chemicals,” which break down very slowly and can contaminate groundwater and end up in rivers and oceans. PFAS chemicals, particularly those with long chains of carbon such as PFOA and PFOS, have been linked to immune, thyroid, kidney, and reproductive problems. PFOA, which has been designated as a possible carcinogen, has a half-life of 92 years in the environment and two to eight years in the human body.

As is so often the case with environmental issues, while steps have been taken to protect Americans from some PFAS chemicals, environmental health advocates and scientists say they don’t go far enough. Now a new study underscores that some common foods can ferry those chemicals into our bloodstream.

Researchers used interviews and biomonitoring data from almost 14,000 people, collected between 2003 and 2014, to build statistical models and find associations. From that federal data set, known as NHANES, they discovered that people who reported eating microwave popcorn had significantly higher levels of four types of PFAS chemicals, according to a study published in Environmental Health Perspectives. The more frequently people ate popcorn, the higher their level of PFAS chemicals in their blood samples.

The study also linked PFAS levels in blood to a diet high in shellfish, which can accumulate those chemicals from contaminated water. One limitation of the research: It measured PFAS chemicals used in past years, while current exposures are more likely to be versions that don’t persist as long in the blood—but are also less well-studied.

Virtually all Americans have detectable levels of PFAS in their blood. But the strongest association in the study revealed an antidote: The more often people ate at home, the lower their level of PFAS chemicals. “In the short term, it’s helpful to know some steps people can take,” says coauthor Laurel Schaider, a research scientist at Silent Spring Institute, the environmental research organization that performed the work. Ultimately, though, the solution to chemical exposure shouldn’t rely on consumer behavior, she says.

So add PFAS to the list of reasons it’s healthier to eat home-cooked food, but don’t despair too much about burgers, pizzas, and popcorn. Political pressure and consumer demand may force a change in food packaging, much the way public sentiment caused companies to remove BPA from plastic bottles and steel can linings.

BPA, or bisphenol-A, is a chemical that mimics estrogen and a component of polycarbonate plastics. In 1992, a Stanford University researcher accidentally discovered that BPA can migrate from a plastic container into its contents, such as food or water. Since then, hundreds of studies have analyzed its health effects, particularly focusing on the neurodevelopment of fetuses, infants, and young children. The NHANES data set revealed that 93 percent of Americans had detectable levels of BPA in their blood.