Breath of Fresh Air: Feature Articles

Chapter 37: Why is asthma becoming more common in recent years?

It does seem that more people are being diagnosed with asthma than ever before and that asthma is becoming a more serious disease. It is possible that in recent years we have focused our attention on this disease and that doctors more often are making the diagnosis of asthma, whereas wheezing and cough and shortness of breath may have received other diagnoses in years past. However, many researchers believe that the frequency of new cases of asthma has truly increased. The short answer to the question of why this might be is: we don't know.

Certain popular explanations — like worsening air quality — do not stand up to close examination. When Germany became a unified country again after the fall of the Soviet Union, it became possible to compare what percentage of the population had asthma in the old East and West Germanies. It turned out that East Germany, with its far worse problems of air pollution from heavy industries, had a lower prevalence of asthma than West Germany.

Two other theories about the rising prevalence of asthma in the United States bear consideration. One explanation suggests that our "tight" houses are to blame. As we emphasized energy efficiency in our homes, we built houses with far less circulation of fresh air. Stimuli that promote the development of asthma — from dust mites to mold to animal danders to second-hand cigarette smoke — are found in higher concentrations in tightly sealed homes. It has been found that when certain populations of people moved from living mostly outdoors in villages to living mostly indoors in confined living quarters, the rate of asthma in the population increased significantly.

Another theory has to do with how our immune system directs its major activities. To the extent that the immune system is called upon to fight certain types of infections, such as tuberculosis, measles, and whooping cough, it is unable to direct its attention at the same time to "fighting" the allergens that we breathe in. On the other hand, as the prevalence of these infections has decreased in modern civilized communities, the immune system is now free to direct its attention to the allergic response. Evidence in support of this hypothesis comes from a recent study conducted in Japan. Researchers found that among young school children with evidence by skin test of having once had a tuberculous infection, asthma was far less common than among the school children who had never been exposed to the tuberculosis germ.

In this sense, asthma may be a disease of civilization. It may reflect on the one hand the decreasing incidence of important infections that influence the direction taken by the body's immune system and on the other hand an increasing exposure in our home environments to stimuli that elicit the allergic response from our immune system.