STEVE PERCIVAL / SCIENCE PHOTO LIBRARY STEVE PERCIVAL / SCIENCE PHOTO LIBRARY
Asthmatic girl using her inhaler. Asthma is a condition in which the small airways (bronchioles) in the lungs constrict, making it difficult to breathe. This causes wheezing, coughing and breathlessness, and can be dangerous. The inhaler releases bronchodilator drugs, which widen the airways. Asthma attacks can be brought on by exercise, allergic reactions and cold weather.
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