Does Pollution Cause Ashtma?

Children exposed to current levels of pollution at virtually no risk of developing asthma

While previous studies showed that air pollution can aggravate pre-existing lung ailments, a new study of children in southern California reports that frequent, strenuous, outdoor exercise, combined with high levels of ozone air pollution, can more than triple children’s risk of developing asthma. This study, published in the Lancet, a prestigious British medical journal, is the first study to find that air pollution might actually cause asthma, not just aggravate it. Officials of the California Air Resources Board, which paid for the study, were quick to claim that its results applied not only to the six southern California communities where it was performed, but also to many cities across the country. ARB officials also maintained that the study justifies additional air pollution regulations in order to protect children’s health. State and local public health officials and advocates echoed these sentiments in the many newspapers that carried the story.

But pollution-control advocates who invoke this study to justify ever more intrusive air pollution regulations are playing fast and loose with the numbers. Though high ozone levels of the past may have caused asthma in some parts of southern California, children exposed to current levels of air pollution are at virtually no additional risk of developing asthma.

In the Lancet asthma study, researchers followed two groups of children in southern California from 1993 to 1998. One group lived in six communities with low pollution levels; the other lived in six communities with high pollution levels. After accounting for factors besides pollution that could account for differences in asthma rates (such as income, ethnicity, parental smoking, etc.) the study found that:

  • Children in high-ozone communities who participated in three or more team sports (about 8 percent of all children in the study) were 3.3 times as likely to become asthmatic when compared with less-active children. Asthma was unrelated to sports participation in the low-ozone communities.
  • Children who spent the most time outdoors were 1.4 times more likely than other children to become asthmatic in the six high-ozone communities, but not in the low-ozone communities.
  • The study also measured other pollutants, such as airborne particulates and nitrogen dioxide, but found no relationship between these pollutants and asthma.
  • Despite the increased asthma rate found for very-active children in polluted areas, asthma rates did not differ overall between the high- and low-pollution areas.

The asthma study estimated children’s ozone exposure using pollution measurements from 1994 to 1997. But southern California has made great progress on air pollution in the intervening years. The communities in the study went from an average of about 34 days per year exceeding the federal ozone health standard, down to an average of just 4 during the last two years a reduction of almost 90 percent. Even Crestline, California, which was not part of the study, but has the worst ozone in the nation, exceeded federal standards an average of 23 days per year for the last two years—about a third less often than the asthma study areas.

Ozone levels are far lower everywhere else. For example, a few other areas of California-San Bernardino, Riverside, Fresno, eastern Los Angeles County and Kern County-have about 5 to 15 high ozone days per year. Ozone across the Houston metro area exceeds the standard from one to 10 days per year. Beyond these regions, no other part of the country averages more than 4 high-ozone days per year, and most have one or none.

In other words, no American experiences ozone at levels similar to those of the asthma study, and more than 97 percent of Americans don’t even experience one-tenth as many high ozone days. Clearly, regulators and public health advocates are wrong when they claim either that the asthma study has something to say about the risks of current air pollution levels, or that current regulations are not sufficient to reduce air pollution.

Proponents of the pollution-causes-asthma hypothesis also err in claiming that air pollution is partly to blame for rising asthma rates during the last 20 years. The Environmental Protection Agency reports ozone levels dropped an average of 24 percent between 1980 and 1999, and other pollutants also declined substantially. Areas with the most ozone pollution experienced the greatest improvement. And the asthma study itself also found no difference in overall asthma incidence when comparing high- and low-ozone communities.

Asthma is a serious disease and no one wants to take risks with their children’s health. But for children to be at risk, they’d need to be frequently exposed to high ozone levels. Fortunately, they’re not. Recent air quality improvements mean that no one in America is now exposed to high ozone as often as in the southern California study.

Asthma exacts a large health toll on our society, making it urgent that we learn what causes the disease and how to neutralize it. But regulators and activists do the public a disservice when they exaggerate health threats. Not only do they scare people for no good reason, they also divert attention and resources from real threats to people—s welfare.

Joel Schwartz is an adjunct fellow at Reason Foundation and visiting scholar at American Enterprise Institute.