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Asthma is the widespread narrowing of small tubes that carry air in and out of the lungs (bronchial airways). The narrowing changes in severity over short periods of time, either spontaneously or under treatment. If you have asthma, the bronchi are more sensitive than normal and certain substances, such as dust mites, animal fur, pollen and cigarette smoke, may trigger or irritate them.
When irritated, the airways narrow making it difficult to breath. This may cause symptoms of wheezing or coughing and the chest to become tight. The narrowing can be reversible, sometimes with the aid of medicines administered by inhalers. However, those with chronic asthma may suffer inflammation which leads to irreversible obstruction of the airways (COAD - Chronic Obstructive Airways Disease).
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