Smarter Living: Family Health

The U.S. is losing ground in the battle with asthma and no one knows why. For the last several decades the number of people with asthma has risen, but between 2001 and 2009 it shot up 12.3 percent, according to a report by the Centers for Disease Control and Prevention (CDC). That means that one in 12 people had asthma in 2009, whereas one in 14 had it in 2001. 24.6 million Americans live with asthma and the worst hit are children, African Americans, women, and the poor.

While the majority of people with asthma have a family history of asthma or allergies, environmental factors also play a role. Traffic exhaust, other air pollutants, tobacco smoke, and indoor allergens (dust mites, cockroaches, dogs, cats, rodents, molds, and fungi) are linked to asthma attacks.

These factors, however, don't fully explain the rise in asthma cases, and the reason for the increase is unclear, especially given reductions in outdoor air pollution, cigarette smoking, and secondhand smoke exposure. "Nobody knows why the asthma rates are going up," says Rachel Miller, deputy director of Columbia Center for Children's Environmental Health, which is studying asthma in urban neighborhoods. "We can say for sure that it is unlikely to be due to genetics because the changes have been too rapid and recent for that."

What Asthma Is

Asthma is characterized by wheezing, chest-tightening, coughing, and difficulty breathing as the airways narrow and swell. These symptoms are triggered when the immune system overreacts to a trigger such as pollen, mold, or dander, although a large number of people have asthma that is triggered by non-allergic factors such as stress, exercise, or viruses.

Genes do play a role in who is susceptible to asthma. A child with one asthmatic parent has a one-in-three chance of developing it. If the child has two parents with asthma, the chances are seven out of ten that the child will have asthma, according to the Asthma and Allergy Foundation of America. People with a family history of hay fever or other allergies are at higher risk of developing asthma.

Yet many people with no family history of asthma go on to develop the condition. This leaves researchers wondering what environmental factors might be to blame. Researchers are exploring a number of these factors, with the most solid evidence pointing to traffic exhaust and air pollution, indoor allergens, and tobacco smoke.

Traffic Exhaust and Air Pollution

Air pollution, especially traffic-related exhaust that comes with living near a highway, has been tied to the development of asthma in a number of studies. In California, the closer children lived to freeways, the greater their risk of developing asthma, according to a report published in the February 2006 issue of the Journal of Occupational and Environmental Medicine. Diesel-powered school buses may expose kids on a daily basis if the buses haven't been upgraded to keep pollution from entering the seating compartment. Air pollution from cars, factories, and power plants contains several components that are linked to asthma, including:

  • ozone, formed when tailpipe pollution reacts with oxygen and sunlight
  • sulfur dioxide, emitted from coal- and oil-fired power plants
  • nitrogen oxides, released from tailpipes and power plants, as well as from indoor gas stoves
  • particulate matter, tiny particles of soot and other contaminants that can lodge deep in the lungs and are produced by a variety of combustion sources including diesel vehicles and coal-fired power plants

Allergens in the Home and Office

Several known asthma triggers are found indoors:

  • cockroach allergens, found in nearly two-thirds of American homes, according to the National Institute of Environmental Health Sciences (NIEHS)
  • dust mites—tiny insects that inhabit bedding, sofas, and cushions
  • pet dander, found in 100 percent of homes surveyed by NIEHS, even those where no pets lived
  • molds and fungi, more likely to be found in damp homes and office buildings where there are water leaks or poor ventilation
  • formaldehyde, a chemical that off-gases from carpets, particleboard, and pressed-wood furniture


Of all the environmental factors being studied as potential causes of asthma, tobacco smoke has the most solid evidence behind it. Young children with asthma are likely to have been born to a mother who smoked during pregnancy or live with parents or caregivers who smoke. And although smoking rates -- at one-in-five adults -- have remained roughly constant over the past ten years, some researchers think that children are spending more time indoors than they used to, which would expose them to secondhand smoke for longer periods than in previous decades.

Under Investigation

Researchers are also looking into potential causes including:

  • heavy metals in dust
  • household pesticides
  • polychlorinated biphenyls (PCBs)
  • poor diet
  • plastics containing phthalates and bisphenol A

These factors are still under investigation, cautions Miller. In all likelihood, one single risk factor is not to blame for all cases of asthma. Also, Miller points out, what may be a risk factor in one individual may be harmless in another because complex conditions like asthma often arise from a combination of a person's genetic makeup and their environmental exposures.

What You Can Do

If you or someone in your family has asthma, make sure the person has an asthma action plan, which details the warning signs of an oncoming attack and what to do about it. The CDC report found that many asthma sufferers were not aware of ways to identify and avoid the triggers of their attacks, or were unaware of how to respond to an attack.

If you live with a smoker, encourage him or her to quit. In the meantime, don't allow any smoking in your home or car. Smoke can also linger on clothes, hair, and skin, where it may pose a health hazard.

Take steps to reduce allergens such as pet dander and dust mites. Damp mop or vacuum regularly and wash bedding in hot water. Use a vacuum cleaner with a HEPA filter (or equivalent fine particle filter). Control indoor humidity: The NIEHS found that humidity and age of the house were the two factors most strongly correlated with dust-mite allergen levels and mold.

Establish a habit of removing shoes before entering the home to keep from tracking pollutants and allergens inside.

If you are purchasing new carpet, repainting your home, or buying furniture, select low-VOC products that do not contain formaldehyde.

Air purifiers may improve indoor air, but must be selected with care. A HEPA air purifier in the bedroom can help reduce levels of allergens and some air pollutants, whereas ozone ‘air purifiers' have been shown to worsen air quality rather than improve it. To learn more about air purifiers, check out the EPA's Guide to Air Cleaners in the Home.

Keep pests such as cockroaches and mice out of your home. Clean the kitchen area regularly and promptly vacuum or sweep up crumbs. To eliminate pests and keep them from coming back, use Integrated Pest Management (IPM), which relies on first making improvements to keep pests out and using the least-toxic pesticide available and only when necessary.

Try to reduce your exposure to traffic exhaust. Choose exercise paths that are at least a couple of blocks from busy streets and take your children to playgrounds that are at least a couple of blocks from busy roadways, especially during peak traffic times.   If you're looking for a new home, try to avoid areas within a few blocks of freeways.

Help improve the air in your community by joining a clean air campaign to reduce truck traffic in your neighborhood or plant trees and increase green space.

Check the Air Quality Index in your area daily at

Help your children avoid school bus diesel exposure. Contact your school district to find out what steps they are taking to address the problem. Schools may decide to retrofit buses, establish no-idling policies, or replace polluting buses with cleaner models. For more ideas, see "The Diesel on the Bus."

Learn More

See NRDC's Air and Asthma page for more about the connection between air pollution and asthma.

Vital Signs: Asthma Prevalence, Disease Characteristics, and Self-Management Education --- United States, 2001-2009

Columbia Center for Children's Environmental Health

National Institute of Environmental Health Sciences: Asthma and Its Environmental Triggers (PDF). May 2006.

last revised 7/13/2011

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