Asthma is a lung disease in which the flow of air out of the lungs is limited by obstruction, but unlike chronic bronchitis and emphysema, this obstruction may be reversible, as it initially does not affect the actual anatomical structure of the airways.

In asthma the obstruction is due to a functional illness in which the airways narrow or constrict through smooth muscle constriction and swelling of the linings of the airways. Between asthma attacks the flow of air through the airways is usually good.

Learn more about asthma in our Asthma Condition Centre.

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