The XX Factor

Does Geography Matter in Childhood Allergies? 

Photo Illustration by Scott Olson/Getty Images

For over a decade now, pediatricians, parents—and perhaps especially the school lunch lady—have become increasingly aware of childhood allergies, particularly of the food-related variety. Stories of reactions (sometimes life-threatening) to nuts, shellfish, and gluten seem increasingly common, and a kid arriving at a birthday party with a list of food restrictions is not unexpected. So what’s going on here? Is there really an epidemic of childhood allergies, and if so, what’s to blame?

A pair of studies out in the past few weeks offer, if not a complete answer, at least some hints. Scientists studying the demographics of childhood allergies have found a correlation between population density and prevalence: Kids in cities are more likely to be sufferers, while rural kids (like the Amish) seem to have fewer problems. Researchers hypothesize that this might be due to the “farm effect” or “hygiene hypothesis,” the notion that children raised around animals and in natural environments more generally are more likely to develop hardier immune systems early-on, while Clorox-wiped urbanites sanitize their children to a fault.

On the one hand, this idea is compelling, if only because it jibes with the current anxiety that our children’s exposure to the outdoors is declining dangerously. But, as Meredith Broussard wrote in Slate back in 2009, these kinds of studies are often dubious in terms of design, not to mention funding sources. The main problem is that researchers rely on responses to surveys, which, of course, are subject to the biases of self-reporting and memory. And parents who take the time to respond to such a survey are likely already invested in the subject emotionally, further clouding their answers.  

So these results are, at best, inconclusive; however, they also may well be onto something—only further research into the actual mechanisms of the farm effect (is the magic in the fresh milk or the hay or both?) will explain the correlation. Until then, getting the kids outside a little more often is probably not a bad idea, but I’d hold off on buying a cow.