Food allergies in kids more common than government said (PICTURES)

(CBS/AP) A surprising new study shows that potentially dangerous food allergies affect about one in 13 kids in the U.S., or about six million kids. That's double a recent estimate by the Centers for Disease Control and Prevention. 

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The CDC estimate, based on in-home interviews, showed that about three million kids have food allergies. The new study is based on online interviews with the parents of more than 40,000 kids under age 18.

The findings, published in the journal Pediatrics, suggest that each classroom in the country has about two kids with food allergies, said study author Dr. Ruchi Gupta, a pediatrician at Chicago's Children's Memorial Hospital.

Dr. Calman Prussin, an investigator with the National Institute of Allergy and Infectious Diseases, said the study "confirms that food allergy is a substantial public health problem."

What explains the big difference between the CDC estimate and what the new study showed? Prussin cited different survey methods and differing definitions of what constitutes a food allergy. He said the only way to know for sure how many kids are affected would be lab tests on scores of children, which is impractical.

He said he new figure doesn't mean prevalence has risen, but experts generally believe allergies including those to food are on the rise, Prussin noted.

He said some people mistake food intolerances for food allergies. For example, some people are lactose intolerant, meaning they can't properly digest milk. That can cause digestive problems, but not an allergic reaction. True food allergies produce symptoms like skin rashes, wheezing, tightness in the throat, or difficulty breathing.

Many children outgrow allergies to some foods, including eggs and wheat. But they're less likely to outgrow allergies to peanuts and other nuts.

The study was funded by the Food Allergy Initiative, a nonprofit advocacy group founded by parents of kids witih food allergies. Mary Jane Marchisotto, the group's executive director, said the study "paints a more comprehensive picture" of food allergies, and should help raise awareness.

The group, funded privately but without industry money, is working with the CDC on national guidelines on how to manage food allergies in schools, she said.

The National Institute of Allergy and Infectious Diseases has more on food allergy.