Croup, also known as laryngotracheitis, is an inflammation and narrowing of the larynx (voice box) and the trachea (windpipe) caused by an infection.

Croup generally occurs in children aged 3 months to 6 years. However, croup over the age of 3 years is uncommon because the windpipe is larger, therefore any swelling is less likely to get in the way of breathing. Most children have only one episode of croup, but a few children have multiple episodes. Croup can occur at any time of year, although...