Nineteen percent of US adults report having one or more food allergies – yet, a little more than one in 10 actually do. That's according to a study recently published in the open-access journal JAMA Network Open.

This means that almost half of all people with a reported food allergy are misinterpreting their symptoms, the researchers say. A team at Northwestern University came to this conclusion after asking a nationally representative sample of more than 40,000 people to list and describe their food allergies.

What’s more, the researchers found that only half of those with a food allergy had a diagnosis confirmed by a doctor. Even less (fewer than a quarter) had an ongoing epinephrine prescription.

So, what exactly is going on here? Lead author Ruchi Gupta, a professor of pediatrics at Northwestern University's Feinberg School of Medicine, suspects that many people who say they are allergic are actually suffering from something like a food intolerance.

"While we found that one in 10 adults have a food allergy, nearly twice as many adults think that they are allergic to foods, while their symptoms may suggest food intolerance or other food-related conditions," Gupta said in a statement.

To be considered a "convincing" food allergy, a respondent had to list one or more of the following symptoms: hives, swelling, difficulty swallowing, throat tightening, chest tightening, trouble breathing, wheezing, vomiting, chest pain, rapid heart rate, fainting or feeling light-headed, and low blood pressure. A food allergy is generally considered to be more severe than an intolerance and can, in a worst-case scenario, trigger anaphylaxis and death.

In contrast, intolerances (although uncomfortable) are not life-threatening. You may even be able to eat small quantities of the food without provoking too many unpleasant symptoms. Speaking of which, most symptoms associated with food intolerances are limited to the gut and digestion. Think IBS and bloating.

Another discovery that struck the researchers was the remarkably high number of people who reported developing an allergy in adulthood. In fact, almost half of adults with a food allergy acquired one or more after their 18th birthday.

“More research is needed to understand why this is occurring and how we might prevent it,” Gupta said.

The survey also reveals what type of food allergies are most common in the US – and shellfish tops the list. Approximately 7.2 million adults have an allergy to shellfish. This is followed by milk (4.7 million), peanut (4.5 million), and tree nut (3 million). Finfish (2.2 million), egg (2 million), wheat (2 million), soy (1.5 million), and sesame (0.5 million) are also frequently reported.

The lesson of the story? It’s always a good idea to get a second (and professional) opinion. A doctor can run tests to confirm or reject your suspicions – and advise you how to manage your condition if it is an allergy. 

“It is important to see a physician for appropriate testing and diagnosis before completely eliminating foods from the diet,” Gupta added.

“If food allergy is confirmed, understanding the management is also critical, including recognizing symptoms of anaphylaxis and how and when to use epinephrine.”

Of course, if you suspect you are allergic to nuts, it is better to avoid them until you can be tested than risk your health for the sake of a peanut butter sandwich.