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The Asthma Section

Asthma and Smog: Does Air Pollution Cause Asthma?

smogAir pollution irritates this lung condition. But could smog cause asthma?

In June of 2005, the smog hanging over downtown Toronto was so thick you couldn’t see the CN Tower from the mid-town restaurant where Sara La Rocque was waiting tables at an outdoor patio. That was when Sara, a 21-year-old creative writing student, quit her job to go home and strip wallpaper.

One day later, she couldn’t breathe properly. Although she had experienced asthma briefly as a child, this was different. It was like breathing through a straw. For most of the rest of the summer, as Ontario lumbered through a record summer of smog advisories, Sara stayed indoors. She was miserable.

It wasn’t until six weeks later that she could even walk around the block with the family’s golden retriever (she is not allergic to dog dander) or the Burmese mountain dog.

Sara’s pretty sure what triggered her condition, and it wasn’t the wallpaper: “My asthma is smog-induced,” she says. “I think that’s what caused it.” A few years ago, most scientists would have doubted her analysis. The common wisdom was that air pollution could only exacerbate symptoms in people already living with asthma.

But now, a handful of mavericks in the scientific world are building a case to prove Sara’s point – that pollution might not just worsen asthma, but cause it. Not that these asthma researchers can yet say how this might happen. That’s still under study.

When it comes to asthma, theories abound as to why it develops, starting with the hygiene hypothesis. This suggests that our urban society is too germ- and virus-free, causing the underworked immune systems of those who inherit the allergic tendency to react to proteins – such as inhaled pollen or dust mites – that should be harmless. The immune system’s over-reaction results in airway inflammation and allergic asthma attacks.

There are also new indications that antibiotics in early life and obesity may be contributing factors. But some scientists keep coming back to the relationship between asthma and air pollution, particularly to that dense layer of smog that blights our cities all too often in the summer.

Somewhere in that haze of pollution, they believe, lies an answer to the mystery of why asthma gets switched on with such frequency in the urban world.

Over the past decade, scientists have found compelling evidence that air pollution irritates the lungs and triggers attacks in those who already have asthma. Some research indicates it can also worsen asthmatic flare-ups to allergens such as pollen, dust mites or pet dander.

“Air pollution remains one of the most under-appreciated contributors to asthma exacerbation,” wrote George Thurston, an associate professor of environmental medicine at New York University School of Medicine, in a 2005 article in the Journal of Allergy and Clinical Immunology.

A classic instance: When a strike closed a steel mill in the Utah Valley for the winter during the mid-1980s, researchers found that admissions of children to hospital for asthma and pneumonia were cut in half – and they climbed right back up the following winter after the steel mill had reopened. That’s a vivid example of pollution’s effect on asthma, and there are plenty more.

Next Page: Proof from California

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