Although labeling is not required by law, sesame causes allergies in more than one million children and adults in the United States, researchers discovered — a figure much higher than previous calculations.

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The study by Northwestern University provided the first up-to-date estimates on the current prevalence of sesame allergy among U.S. children and adults in all 50 states. It was published at the JAMA Network Open journal.

“Our study shows sesame allergy is prevalent in the U.S. in both adults and children and can cause severe allergic reactions,” said lead study author Dr. Ruchi Gupta. “It is important to advocate for labeling sesame in packaged food. Sesame is in a lot of foods as hidden ingredients. It is very hard to avoid.”

The study looked at ongoing regulatory rule-making by the U.S. Food & Drug Administration, which is currently considering whether sesame should be added to the list of key food allergens for which mandatory product labeling is required.

While some other countries do, the U.S. doesn’t require sesame-containing products to be labeled. Only the labeling of the top eight allergenic foods/food groups is required: peanuts, milk, shellfish, tree nuts, egg, wheat, soy, and finfish (along with proteins derived from them).

The study found that there are more than 1.5 million children and adults in the U.S. that report a current sesame allergy, and more than 1.1 million that report either a physician-diagnosed sesame allergy or a history of sesame-allergic reaction symptoms. This figure dwarfs previous estimates and raises some serious concerns about the prevalence of this allergy.

Sesame allergy affects children and adults to a similar degree, unlike allergies such as milk or egg, which often develop early in life and are outgrown by adolescence. In addition, the study found that four in five patients with sesame allergy have at least one other food allergy. More than half have a peanut allergy, a third are tree-nut allergic, a quarter is egg-allergic and one in five is allergic to cow’s milk.

Study investigators carried out a survey via telephone and web to more than 50,000 U.S. households. The survey asked detailed information about any suspected food allergies, including specific allergic reaction symptoms, details about the clinical diagnosis of food allergies as well as demographic information.