These days, it can seem like just about everybody has a food allergy. But according to a new study, about 11% of American adults actually do.

Yet 19% of adults believe they have a food allergy, even though some don’t have the diagnosis or symptoms to back it up, according to findings published in JAMA Network Open.

This discrepancy suggests that quite a few adults are conflating allergies with less-severe food intolerances, which typically come with minimal digestion-related symptoms, the researchers write. If someone is truly allergic to a food, eating it can trigger a potentially life-threatening immune response. (People who are lactose intolerant, for example, may experience bloating, stomach pain and gas after eating dairy products, while those with a true milk allergy can experience wheezing, hives and anaphylaxis.)

The new estimates were based on survey responses from almost 40,500 American adults who were asked if they had any diagnosed allergies, symptoms or hospitalizations. The researchers couldn’t independently confirm whether each survey respondent actually had a food allergy, but allergies were considered “convincing” if the person reported a physician’s diagnosis or significant symptoms such as swelling, trouble breathing, chest pain, vomiting or fainting after eating a certain food. Reports of an allergy that were only backed by milder symptoms, such as itching, stomach pain and rashes, did not meet the researchers’ criteria.

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They found that almost 11% of people had at least one convincing food allergy. The most common allergens were shellfish (2.9%), milk (1.9%), peanuts (1.8%), tree nuts (1.2%) and fin fish (0.9%), according to the study. Extrapolated to the national level, that means an estimated 7.2 million American adults are allergic to shellfish, 4.7 million are allergic to milk, 4.5 million are allergic to peanuts, 3 million are allergic to tree nuts and 2.2 million are allergic to fin fish.

About 45% of the adults with a food allergy had more than one, the researchers found.

Food allergies are also common in children, affecting about 8% of American kids, but many childhood allergies can be outgrown. Other times, allergies can start in adulthood: About 48% of people with allergies in the new study reported developing at least one of their conditions as an adult.

Despite the relatively high rates of food allergy — and the fact that 40% of people with an allergy had visited the emergency room because of it — the researchers found that only 47.5% of those with an allergy had been officially diagnosed by a doctor. Getting verification from a doctor, the authors write, could help true allergy sufferers get the treatment and avoidance tips they need — and spare those with only intolerances from a lifetime of unnecessary precautions.

Write to Jamie Ducharme at jamie.ducharme@time.com.