Croup is swelling in the voice box and wind pipe. The swelling can make it difficult to breathe. This can cause a barking cough. Croup occurs most often in children between age six months and three years. This is because young children have a smaller airway. Airways become wider as children grow. This decreases the chance of croup in older children and adults.

Upper Respiratory System in a Child
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Croup is caused by viral infections such as: