Coming Soon to a Highway Near You: Asthma, The Disease

BY ON October 5, 2012

Clogged highway in LA

A couple of years ago, when I developed a persistent cough and was wheezing, I paid a visit to my doctor. He asked me if I had asthma as a child. “Well, yes,” I said. “But that was 30 years ago. I haven’t had it for decades.” That didn’t matter to him. “You never get rid of asthma,” he said. “Once you have it, you always have it.”

There is a difference between asthma, the disease, and asthma, the symptoms. And although doctors and asthmatics understand that traffic pollution triggers asthma symptoms, a recent study shows that the impact of traffic pollution on asthma — the disease — has been underestimated, and is significant.

Asthma causes are the things that cause a person to develop the underlying disease known as asthma. Asthma triggers, on the other hand, are the things that cause a person with asthma to develop symptoms such as wheezing and coughing, also known as an asthma attack.

Asthma triggers are relatively well understood. They include things like tobacco smoke, pets, traffic pollution, power plant pollution, diesel exhaust, pesticides, dust mites, and volatile organic compounds (VOCs) such as those found in paint and household cleaners. But the causes of asthma are more elusive. Asthma, the disease, is generally understood to be an inflammatory disease caused by a combination of genetics and environmental factors.

In recent years, however, the picture has been getting clearer. Public health research on the effects of air pollution has found that exposure to some pollutants, such as diesel exhaust, not only triggers asthma attacks but also actually causes the development of the underlying disease in some people. At the same time, communities have noticed (and researchers have confirmed) that people living near obvious sources of air pollution, such as busy highways, bus depots, and refineries, have more asthma than people living farther from these pollution sources.

According to a team of scientists that recently analyzed the burden of asthma among children in Los Angeles,

“…a scientific consensus is emerging that the observed epidemiological associations of higher asthma incidence along major roads are causal.”

“Causal” is an important word in public health, and it’s not entered into lightly in a peer-reviewed journal. Researchers can detect “associations” and “correlations” till they’re blue in the face, but that doesn’t prove anything about causality. Living near traffic may go together with having asthma, but who’s to say that one causes the other? It takes a lot of careful research to determine that these two things are related in a causal way.

Once we accept that living near traffic causes asthma, it alters the way we understand the disease. The group that looked at asthma in LA showed us how. Using data on traffic pollution, asthma, and location of residence, they calculated that 8% of all childhood asthma in LA county is caused at least in part by living near a major roadway. In other words, traffic pollution in Los Angeles has caused more than 27,000 otherwise healthy children to develop asthma.


Although this study did not discuss other cities, it is likely that other densely population urban areas also face an increased asthma burden due to people living near major roads.

Asthma has multiple causes, and many possible triggers. Many of these (smoking, home pesticide use, dust mites) are things we can control. But to the extent that traffic pollution causes asthma, we need to work together as a Force. Whether it’s making sure that urban planning initiatives consider the implications of siting housing near highways, or building mass transit infrastructure that reduces traffic pollution, or requiring our car fleet to innovate toward cleaner technology, we need to make sure that policies are put in place that protect our kids from this cause of illness.

Photo: Bart Everett /


TOPICS: Asthma, Clean Air Rules and Regulations, Pollution