Croup is an infection causing a partial blockage of air as it flows through the larynx (voice box). The noise can be very frightening, and your child's cough may sound like a seal barking. When your child breathes in you may hear a harsh, rasping sound, which is called stridor. The child's voice may be hoarse, too.
Croup may appear after your child has had a cold for several days. Croup is usually caused by a virus and may last several days. Sometimes croup comes on suddenly in the middle of the night. It may disappear in as little as a few hours. It may occur more than one time in a child's life.