What Causes Asthma: Asthma

Content provided by the Faculty of the Harvard Medical School

What causes asthma?

No one knows exactly what causes asthma. It is not even clear whether asthma is one disorder or a group of disorders with similar manifestations. Still, much has been learned about who is most likely to develop asthma and how an asthma attack occurs. To put it simply, a person becomes susceptible to developing asthma because of genes, but develops the disorder only after exposure to things in the environment that stimulate the immune system in such a way that the airways become inflamed and prone to attacks.

A simple example may help explain how genetic and environmental factors can interact to produce asthma. Suppose you inherit a tendency to be allergic to cockroaches. After many years of living in a single-family house, you move to an apartment complex. The good news is that you don't have to mow the lawn anymore — but you may also find yourself living with cockroaches for the first time in your life. This can lead over time to an allergic irritation of your bronchial tubes. Once irritated or inflamed in this way, your bronchial tubes react not only to cockroaches but also to many other types of stimuli that typically make asthma worse, such as smoke, exercise, and respiratory infections. After many months or years of exposure, even if you move out of the apartment into one that doesn't have a cockroach problem, this hypersensitivity of your airways — in other words, your asthma — may persist.

Last updated:	September 27, 2007