Asthma is a chronic (long-lasting) inflammatory disease of the airways. It causes the airways to narrow periodically. This produces wheezing and breathlessness. Obstruction to air flow either stops spontaneously or responds to treatment, but continuing inflammation makes the airways hyper-responsive to stimuli such as cold air, exercise, dust mites, air pollution, stress, and anxiety.

About 10 million Americans have asthma, and the number seems to be increasing. Between 1982-92, the rate rose by 42% and the death rate from asthma increased by 35%.

Changes that take place in the respiratory system of an asthmatic person make the airways (the bronchi and the smaller bronchioles) reactive to stimuli that don't affect healthy people. In an asthma attack, the muscle tissue in the walls of bronchi spasm, and the cells lining the airways swell and secrete mucus into the air spaces. Both these actions cause the airways to narrow which makes breathing more...