Asthma is a lifelong affliction—crippling and expensive to manage. But it doesn’t affect everyone the same. The disease is much more prevalent among black and Puerto Rican children.

A new working paper, published in the National Bureau of Economic Research, demonstrates that it’s the characteristics of places, not people, that are largely responsible for that disparity. So while a slew of related factors—income and education, birthweight, disparate access to health care—play a role in the prevalence of asthma, they may often be a reflection of where a person lives.

In New Jersey neighborhoods with a significant shares of black residents, all children—regardless of race—are at higher risk for asthma, the paper finds. Janet Currie, a professor of economics and public affairs at Princeton University, and Diane Alexander, of the Federal Reserve of Chicago, conclude:

Our estimates suggest that black ZIP codes are less healthy places for all children, and that much of the gap in asthma rates between African-American and other children in New Jersey is attributable to their place of residence.

For their analysis, the researchers accessed government health records between 2006 and 2010 of all children born in the state. This extensive dataset included information about their race, birth weight, residence, characteristics of their parents, and emergency room visits. Using it, they compare asthma rates in kids in “black ZIP codes”—(neighborhoods which contained at least 27 percent black children)—to those living elsewhere. Then, they do the same with black and non-black kids within these ZIP codes.

It’s important to note that the 27 percent threshold, by the authors’ own admission, is arbitrary. But it’s significant because over 60 percent of all black kids in their sample resided in these 94 “black ZIP codes,” which means that the health disadvantages of this space established in this paper are disproportionately borne by this group. The second benefit of using that threshold is that it allows an apples-to-apples comparison of black and non-black kids within these ZIP codes, because the numbers of children in the two groups are roughly similar.

Upon crunching the numbers, the researchers find that black and white kids in “black ZIP codes” were a little over 4 percentage points more likely to suffer from asthma, compared to their counterparts who lived elsewhere. Within these minority-heavy neighborhoods, the difference in asthma prevalence disappeared between the races, after accounting for birth weights.

While the researchers didn’t have the kind of granular pollution data to show that these ZIP codes have poorer air, previous research supports that case. Currie and Alexander have, however, included maps that show the proximity of “black ZIP codes” to various sources of pollution. These areas tend to be half the distance away from factories than other neighborhoods, on average. And a larger share of their residents live close to busy highways.

Maps by Janet Currie and Diane Alexander/Madison McVeigh

Other physical and socio-economic characteristics of these neighborhoods contribute to the disparity, too. These ZIP codes tend to be poorer, less educated, and further away from quality health care. The housing stock tends to be at least 7 years older and often vacant, making it more likely that mould, vermin, and other in-house irritants that trigger asthma.  

This paper adds to an authoritative body of evidence that the ZIP code determines, to a large extent, the future of a child living in America. That isn’t a de facto occurrence. The long spell of discriminatory housing policies endorsed by government have funneled certain groups into areas with fewer economic and academic opportunities, and unhealthier environments. Of course, measures to clean up these neighborhoods, limit factory emissions, and decongest highways are warranted. But they might not be enough, and they might have unintended negative consequences such as gentrification. “You can take a neighborhood that’s sort of crummy with lots of sources of pollutants and you clean it up—and then you get Brooklyn,” Currie says.

That’s why many advocates also call for policies that improve access to cleaner and healthier neighborhoods, such as more dispersed affordable and subsidized housing units.