For over 26 million US adults, food allergies are serious business — the merest whiff of a peanut or a bit of shellfish hidden in a stew could cause serious harm, as in the case of 11-year-old Cameron Jean-Pierre, who died this week from being in the same house as cooking seafood. But for a surprisingly large number of people, years of careful efforts to steer clear of certain foods might be unwarranted, per the results of a study released Friday in JAMA Network Open.

Ruchi Gupta, M.D., M.P.H., a professor at Northwestern University’s Feinberg School of Medicine and the lead author of the new study, makes the case that roughly half of the food allergies that people self-diagnosed in her survey of 40,433 adults may not actually be allergies — they might be something else entirely. To be clear, she’s not talking about people who have had their allergies to foods like peanuts, shellfish, and gluten diagnosed by an allergist. Her survey deals with people who have been avoiding these foods all their lives because they believe they have an allergy but have never actually been diagnosed with one.

“It was kind of a shocker that so many adults were avoiding foods because they thought they had a food allergy,” she tells *Inverse. “But when we cleaned [the data] it was half of that [number].”

Peanut allergies aren't the most common allergies, but they're the ones that are more often diagnosed. Pixabay

To show this disparity, Gupta was rigorous with her definition of food allergies. She began by asking patients to self-report their allergies — that’s how she came up with her first number — about 19 percent of her participants reported allergies to common foods like shellfish, milk, and peanuts.

Then she checked patients against themselves by asking them to elaborate on symptoms of that allergy. If the patient’s reported symptoms didn’t match those traditionally seen in people who had been diagnosed with a food allergy, she removed them from her dataset. When she did, that initial 19 percent of people who reported allergies dwindled to 10.8 percent who she and her co-authors believe had “convincing” food allergies. It’s admittedly a broad, non-experimental approach, but an illustrative one all the same.

That’s not to say that these individuals didn’t have adverse, uncomfortable reactions to these foods, says Gupta, but she indicates that those reactions might not represent full-blown allergies.

“What I think is so important about that huge number — that one in five adults — is that adults are having an adverse reaction, and they’re labeling it as a food allergy, which makes sense,” Gupta tells Inverse. “But it could really be some other food-related condition that might be more treatable. It may not be life-threatening.”

Milk was the second most common food allergy identified in the study. Pxhere

Take, for instance, milk allergies, found by 1.9 percent of the survey respondents. Gupta explains that people often report bloating, pain, or diarrhea from milk-drinking, and they often classify this reaction as a milk allergy. Instead, these are the symptoms of lactose intolerance — a condition in which the body doesn’t manufacture the correct enzyme needed to break down lactose in milk.

"“It was kind of a shocker that so many adults were avoiding foods because they thought they had a food allergy."

Biologically speaking it’s a different phenomenon that an actual milk allergy — which means that the body’s immune system has a dramatic reaction to some of the proteins present in cows milk. Gupta also adds that even tingling sensations that some people might feel in their mouths or throats — importantly different than the sensation of throat closing, a typical sign of an allergic reaction — could represent environmental allergies like pollen that simply made their way onto the food.

The way to know for sure, she adds, is to get tested by an allergist so you can tell the difference between an adverse reaction and an allergy that might require special treatment — her survey found that only about 47.5 percent of adults who likely do have food allergies actually got an official diagnosis.

Overall, she found that shellfish allergies — which tended to develop during adulthood and she estimates affect 7.2 million adults — were the most common in her sample. That was followed by milk allergies, which she predicts affect 4.7 million adults, and peanut and tree nut allergies, which she estimates affect 4.5 million and 3 million adults respectively.

Gupta’s survey serves to highlight that adult food allergies are still surprisingly common, just not as common as some people believe.