Croup is a condition that causes an inflammation of the upper airways — the voice box (larynx) and windpipe (trachea). It often leads to a barking cough or hoarseness, especially when a child cries.
Most cases of croup are caused by viruses. Those involved are usually parainfluenza virus (which accounts for most cases), adenovirus, and respiratory syncytial virus (RSV). Croup is most common — and symptoms are most severe — in children 6 months to 3 years old, but can affect older kids, too.
Most cases of viral croup are mild and can be treated at home, though rarely it can be severe and even life-threatening. Some children are more prone to developing croup when they get a viral upper respiratory infection.
The term spasmodic croup refers to a type of croup that develops quickly and may happen in a child with a mild cold. The barking cough usually begins at night and is not accompanied by fever. Spasmodic croup has a tendency to come back again (recur).