Bronchiolitis is a childhood disease that affects the lungs. It occurs when a virus enters the breathing system. The virus causes the tiny airways in the lungs to become swollen. As a result, a thick fluid called mucus collects in the airways. This makes it hard for air to flow freely in the lungs.

Bronchioles
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Bronchiolitis is caused by a virus. There are several different types of virus that may cause it. The viruses are easily spread from person to person like a common cold. It spreads most often through coughs or sneezes which release droplets of moisture into the air. Breathing in the air can cause the infection in a noninfected person.