By Stephanie Stahl

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PHILADELPHIA (CBS) — Food allergies usually develop in children but four percent of American adults also have them. And while a new survey says some people falsely think they’re allergic, the numbers are climbing.

Christine Collins carries her EpiPen everywhere. The 42-year-old developed a life-threatening food allergy to shellfish in her 20s after eating seafood her entire life.

“It felt like my throat was closing up like. By the time we were in front of the ER I couldn’t breathe so that’s how fast it happened,” said Collins.

New research shows an estimated 26 million adults have a food allergy in the U.S., that’s 1 in 10 adults. And nearly half developed at least one of their allergies in adulthood like Christine.

“One it certainly points to this being a very prevalent issue and likely more prevalent than we previously recognized, particularly the adult onset,” said Dr. Wayne Shreffler, director of the food allergy center at Massachusetts General Hospital.

The study surveyed over 40,000 adults and found shellfish was the most common food allergy in adults, followed by milk, peanut, tree nut, other fish, egg, wheat, soy and sesame.

But researchers also found many adults believe they are allergic to foods when they’re instead more likely suffering from food intolerance or a health condition.

“Patients need to get a proper diagnosis so that if they are at risk of severe reactions they are prepared to deal with them. It’s also important because it can be misdiagnosed and people can think they are allergic to the wrong things and avoid foods unnecessarily,” said Shreffler.

Christine knows how important the right diagnosis is.

“Get checked out by an allergist you don’t want to find out the hard way,” she says.

In addition to carrying an EpiPen, she now wears a medical alert bracelet to stay safe.

The study also found half of the patients with adult-onset allergies had very serious reactions that sent them to the ER.

Food allergies are on the rise in adults as well as children.

Allergies develop when your immune system mistakenly identifies a substance such as pollen, mold, animal dander, or food as harmful.

Stephanie Stahl