When Ina Chung, a Colorado mother, first fed packaged foods to her infant, she was careful to read the labels. Her daughter was allergic to peanuts, dairy, and eggs, so products containing those ingredients were out. So were foods with labels that said they may contain the allergens.

Chung felt like this last category suggested a clear risk that wasn’t worth taking. “I had heard that the ingredient labels were regulated. And so I thought that that included those statements,” said Chung. “Which was not true.”

Precautionary allergen labels like those that say "processed in a facility that uses milk" or "may contain fish" are meant to address the potential for cross-contact. For instance, a granola bar that doesn’t list peanuts as an ingredient could still say they may be included. And in the United States, these warnings are not regulated; companies can use whatever precautionary phrasing they choose on any product. Some don’t bother with any labels, even in facilities where unintended allergens slip in; others list allergens that may pose little risk. Robert Earl, vice president of regulatory affairs at Food Allergy Research & Education, or FARE, a nonprofit advocacy, research, and education group, has even seen such labels that include all nine common food allergens. “I would bet my bottom dollar not all of those allergens are even in the facility,” he said.

So what are the roughly 20 million people with food allergies in the US supposed to do with these warnings? Should they eat the granola bar or not?

Recognizing this uncertainty, food safety experts, allergy advocates, policymakers, and food producers are discussing how to demystify precautionary allergen labels. One widely considered solution is to restrict warnings to cases where visual or analytical tests demonstrate that there is enough allergen to actually trigger a reaction. Experts say the costs to the food industry are minimal, and some food producers across the globe, including in Canada, Australia, Thailand, and the United States, already voluntarily take this approach. But in the US, where there are no clear guidelines to follow, consumers are still left wondering what each individual precautionary allergen label even means.

Pull a packaged food off an American store shelf and the ingredients label should say if the product intentionally contains one of nine recognized allergens. That’s because in 2004, Congress granted the Food and Drug Administration the power to regulate labeling of eight major food allergens—eggs, fish, milk, crustaceans, peanuts, tree nuts, soybeans, and wheat. In 2021, sesame was added to the list.

But the language often gets murkier further down the label, where companies may include precautionary allergen labels, also called advisory statements, to address the fact that allergens can unintentionally wind up in foods at many stages of production. Perhaps wheat grows near a field of rye destined for bread, for instance, or peanuts get lodged in processing equipment that later pumps out chocolate chip cookies. Candy manufacturers, in particular, struggle to keep milk out of dark chocolate.

The FDA offers no labeling guidance beyond declaring that “advisory statements should not be used as a substitute for adhering to current good manufacturing practices and must be truthful and not misleading.”

Companies can choose when to use these warnings, which vary widely. For example, a 2017 survey conducted by the FDA and the Illinois Institute of Technology of 78 dark chocolate products found that almost two-thirds contained an advisory statement for peanuts; of those, only about four actually contained the allergen. Meanwhile, of 18 bars that carried no advisory statement for peanuts specifically, three contained the allergen. (One product that was positive for peanuts did warn more generally of nuts, but the researchers noted that this term is ambiguous.) Another product that tested positive included a nut warning on one lot but not on another. Individual companies also select their own precautionary label phrasing.

For consumers, the inconsistency can be confusing, said Ruchi Gupta, a pediatrician and director of the Center for Food Allergy & Asthma Research at Northwestern University’s Feinberg School of Medicine in Chicago. In 2019, Gupta and colleagues asked around 3,000 US adults who have allergies or care for someone who does about how different precautionary allergen label phrases make a difference when they are considering whether to buy a particular food. About 80 percent never purchase products with a may contain warning. Less than half avoid products with labels suggesting that it was manufactured in a facility that also processes an allergen, even though numerous studies show that the wording of a precautionary allergen label has no bearing on risk level. “People are making their own decisions on what sounds safe,” said Gupta.

When Chung learned that advisory labels were unregulated, she experimented with ignoring them when her then-toddler really wanted a particular food. When her daughter developed a couple of hives after eating a cereal labeled may contain peanuts, Chung went back to heeding warnings of peanut cross-contact but continued ignoring the rest.

“A lot of families just make up their own rules,” she said. “There's no way to really know exactly what you're getting.”