The Link Between Air Pollution and Asthma

If you have asthma, air pollution can trigger symptoms and cause an attack. Find out what you can do to reduce your risk.

Imagine not being able to drive with the car windows open because the outside air makes it difficult to breathe. While the scenario may sound like something out of an apocalyptic film, it's common for people with asthma at times when air quality is poor. Research shows that air pollution undermines asthma control for people in cities and towns all over the country.

Why Air Pollution Triggers Asthma
While air pollution does not cause asthma, it can definitely trigger asthma symptoms or an asthma attack if you already have this condition.

Are you doing everything you can to manage your asthma? Find out with our interactive checkup.

“We know that people with asthma, children and adults, can have an aggravation of their asthma when [pollution] levels in the air are higher,” says Kenneth Rosenman, MD, chief of the division of occupational and environmental medicine at Michigan State University in East Lansing, Mich. “There are studies [of] kids living in neighborhoods around the approaches to bridges or tunnels, showing they have more respiratory problems than kids living out in the country somewhere. It [pollution] clearly can aggravate [asthma symptoms]. When there are air pollution episodes, when the levels are higher, we consider asthmatics to be a susceptible population.”

An asthmatic's airways can be considered “hypersensitive,” which means elements in the air cause inflammation and constriction that lead to coughing, wheezing, and shortness of breath. “We describe an asthmatic as someone who has sensitive airways the same way some people have touchy skin. Any irritating stimulant, like cigarette smoke or ozone, that may not produce a reaction in a non-asthmatic person will lead to wheezing or an attack [in an asthmatic],” explains Richard Castriotta, MD, professor of medicine and associate director of the Division of Pulmonary, Critical Care, and Sleep Medicine at the University of Texas Houston Medical School.

Understanding Ozone
One of the leading contributors to outdoor air pollution is ozone, whose basic unit consists of three oxygen molecules. Ozone gas is usually found in the earth’s upper atmosphere where it forms a protective barrier against harmful rays from the sun, but it can also form in the lower atmosphere, where people can breathe it in. Under certain conditions — usually in the warm, sunny days of summer — ozone collects in the lower atmosphere, contributing to the smog, haze, or “air pollution” that obscures city skylines. This layer of pollution is a result of sun and heat acting on the oxygen and many other substances, including chemicals released by chemical plants, gas pumps, power plants, and vehicle emissions.

The risk of asthma rises as the concentration of ozone in the air rises, according to hospitalization data on more than a million children between 1995 and 2000. With each increase of ozone by one part per billion (a measure of its concentration in the air), the risk of asthma hospitalization went up 22 percent, with children under age 2 at the greatest risk.

Preventing Asthma When Ozone is High
Many cities and local news channels now alert the public when ozone levels are considered dangerous for people with asthma. You can also check the Web site of the Environmental Protection Agency ( for up-to-date information.

To avoid an asthma attack on high ozone days, try the following these suggestions:
  • Exercise indoors or early in the day when ozone levels are lowest. As the day progresses and the temperature rises, ozone levels also get higher.
  • Stay away from high-traffic areas. Don’t go walking along the freeway or places where cars tend to idle. Keep in mind, though, that living in a rural or suburban area doesn’t necessarily protect you; ozone related to vehicle emissions can drift hundreds of miles.
  • Make sure you know what to do if you start to experience asthma symptoms.
  • Use ozone-reducing air filters indoors to control the ozone entering your home, although on high-alert days you should keep the doors and windows closed as much as possible.
If you have asthma, know where to get accurate and timely information on ozone levels in your area, and be sure to check these sources frequently. Be willing to change your daily routine so that you can stay indoors if air quality is poor — your lungs will thank you for it!
Last Updated: 01/20/2012

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