Chemicals that have been associated with cancer and other health problems have been found in some fast-food packaging, according to a new study. Researchers found the substances, which can leach into food, in sandwich and dessert wrappers and paperboard containers.

“We have more than one reason to try to eat more fresh food, and to reduce our consumption of fast food,” said Laurel Schaider, one of the study’s authors, and a research scientist for the Silent Spring Institute. “This is another reason.”

The chemicals, per- and polyfluoroalkyl substances (PFASs), are used in nonstick, stain-resistant and waterproof products. Fast-food packaging manufacturers might use them to keep sauces or grease from leaking through the wrapper. (Consumers are also exposed to them in other products, such as certain types of cookware, coats and carpets.) Some of the substances in this category are associated with kidney and testicular cancer, low birth weight, thyroid disease and immunotoxicity in children, among other outcomes.

Schaider and her team tested wrappers from 27 fast-food companies, including McDonald’s, Wendy’s, Starbucks and Panera Bread. One-third of all samples tested contained detectable concentrations of flourine, a marker for PFASs. The food packages that were most likely to contain the fluorine were paper wrappers for desserts and sandwiches. Paper board — such as the stiff containers for french fries or pizza — also contained fluorine. Paper cups for beverages were in the clear, though.

Before you panic: “It’s really difficult to make that link between what we were finding in the packaging, and how that might affect someone’s health,” said Schaider. “PFASs are a complex category.”

According to the Center for Disease Control’s Agency for Toxic Substances and Disease Registry, some PFASs “have shown changes in the liver, thyroid, and pancreatic function, as well as some changes in hormone levels.” They also can increase cholesterol and cancer risk, though more study is needed to understand exactly how these substances — and in which combination — can affect a person’s health.

The study, published in the journal “Environmental Science & Technology Letters,” did not examine how much of the chemical migrated into food, though Schaider noted that other studies have found that such a transfer is possible, especially if the food is hot or contains emulsified fats, such as mayonnaise. Dessert and bread wrappers, and Tex-Mex food packaging were found to be the mostly likely to contain the chemicals. Schaider declined to call out certain brands for their packaging, because she said her sample size was small.

Besides, fast food is not our only exposure to such chemicals: We might inhale them as dust from a stain-resistant carpet, or ingest them from plant-or-animal food sources that have absorbed them in their environment. And even though we might think of the paper wrapper for, say, a coffeeshop scone as being recyclable, recycling a PFAS-containing wrapper can have deleterious effects on the environment, because the substances do not degrade quickly and can leach into groundwater.

Another interesting finding was the fact that, of 20 samples chosen for a more detailed analysis, six contained perfluorooctanoic acid, a type of PFAS that U.S. manufacturers voluntarily agreed to phase out in food-contacting products in 2010, through an Environmental Protection Agency initiative. When Schaider and her team reached out to fast-food companies to see if they were aware of the substances in their packaging, they received only two responses, both from companies who believed that their packaging was PFAS-free, even though it wasn’t.

But the good news is that many wrappers Schaider and her team tested did not contain PFASs, which means there are chemical-free alternatives in the market.

“We know these chemicals are highly persistent. We know that nearly all Americans are exposed to these chemicals. They’re used for purposes that we don’t need, or we could find a substitute,” she said. “Consumers who are concerned about exposure to these chemicals can let fast-food companies know that they’d rather not have PFASs in the packaging that wraps their food.”