Asthma is an inflammatory condition of the airways of the lungs. The airways (bronchial tubes) are sensitive to irritating substances such as dust, animal fur and cigarette smoke. These irritants are known as trigger factors. When someone with asthma comes into contact with a trigger factor their airways narrow and produce a sticky mucus (phlegm), making it difficult for air to pass through.
The exact cause of asthma is unknown, but attacks can be caused by an allergy to a trigger factor. The
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