Why are city kids more prone to food allergies?

City children are more likely to suffer from food allergies than their counterparts in rural areas, according to a study in the July issue of the journal Clinical Pediatrics. The new study is the first to map children's food allergies according to where they live in the United States, says Dr. Ruchi Gupta, an assistant professor of pediatrics at the Northwestern University Feinberg School of Medicine. Is it time for city dwellers to pack up and move to the countryside? Here, a brief guide:

What exactly did the study find?

Nationwide, about one child in 13 suffers from a food allergy — but some areas are more affected than others. Researchers asked the parents of 38,500 children under age 18 about their children, and found that 9.8 percent of the kids who lived in areas with urban zip codes had food allergies, compared to just 6.2 percent of those in rural communities. The gap was found for all sorts of food allergies, from peanuts to shellfish. "That's a big discrepancy," says Gupta. "The big question now is what in the environment is the trigger?"

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What might be to blame?

One possible explanation is the "hygiene hypothesis." The human body needs to be exposed to bacteria early on to develop a healthy immune system. Germaphobic Americans in big cities may have become too clean, wiping out bacteria with hand sanitizers and anti-bacterial gels instead of letting the body learn to fight them, causing our immune systems to "fight things [they] shouldn't be fighting," Gupta says. "But right now, this is just a theory. Nothing is proven."

Could there be another cause?

There are several aspects of city life that might contribute to the problem. Perhaps pollution is to blame, or changes in our food supply. In cities, Americans have increasingly moved away from locally grown foods and started eating more processed foods, and that might have contributed to the rise in allergies.

What can urban parents do?

It's hard to say, at least until further research pinpoints what exactly makes allergies more common in densely populated areas. In the meantime, some schools have established themselves as "peanut-free zones," banishing the once-ubiquitous peanut butter and jelly sandwich from the cafeteria in the name of protecting children with severe allergies. Chicago schools are starting to stock epinephrine auto-injectors to save children who have life-threatening allergic reactions. Awareness is key, Jennifer Jobrack, the Midwest director of the Food Allergy Initiative, tells the Chicago Tribune. "You always have to be vigilant on behalf of your child."

Sources: CBS News, Chicago Tribune, MSNBC, Mommyish