City kids have a smorgasbord of food choices. But they also face food allergies more than do their country cousins.

Researchers mapped food allergies in children across the U.S. And they found more cases per capita in areas with higher population densities. The work is in the journal Clinical Pediatrics. [Ruchi S. Gupta et al., "Geographic Variability of Childhood Food Allergy in the United States"]

The scientists collected allergy information on more than 38,000 Americans under age 18, and then sorted the information by zip code. Six percent of children in rural areas had a food allergy. But that number jumped to 10 percent of kids in urban centers. Peanut and shellfish allergies in particular were more common. Although the frequency of allergies varied by location, their severity did not.

What explains this trend? It could be that rural dirt is good—in the country, children’s immune systems get challenged early and often, and thus more properly trained. Or it could be that urban dirt is bad—city children deal with pollutants that may predispose them toward allergies.

Solving this puzzle could help protect kids from common foods that can do them uncommon harm.

—Sophie Bushwick

[The above text is a transcript of this podcast.]