Croup is an infection of the tissues around the vocal cords in young children. It causes a characteristic barking cough.
The symptoms of croup are caused by the swelling and inflammation of the tissues around the larynx and vocal cords. The diameter of the upper airway in young children is narrow to begin with, so this swelling further reduces the size of the airway. This makes breathing noisier and more labored.
When a virus that can cause croup moves through a community, only some children will develop croup. Most children will have symptoms of a cold or laryngitis, such as congestion, cough, hoarseness, or sore throat.
The parainfluenza virus is a family of viruses that accounts for 75% of cases of croup. Croup generally affects young children between 3 months and 5 years of age. Boys are affected more often than girls. About 15% of children with croup have a family history of croup. Some children have repeated episodes of croup.