It looks like: A simple cold, sometimes with a fever, until the coughing starts a few nights later. Croup almost always comes on after midnight. The raspy, barking cough and high-pitched whistle when Baby inhales (called stridor) are so distinct, doctors can often diagnose croup over the phone. "That seal sound! The first time my daughter Zoe had that cough, I thought, This is what they're talking about. It's so obvious," Darien Wilson, of Highlands Ranch, Colorado, says.
What's happening: Babies get croup when a virus causes swelling in the larynx, vocal cords, and windpipe. An infant's windpipe is narrow to begin with, and the swollen vocal chords are very close together. When babies get scared and cry, the airflow through the larynx as they breathe in or cough produces croup's telltale bark and whistle, Dr. Beno explains. Some reassurance: The virus that causes most cases is so benign that kids will often get only that barky cough, Dr. Cardona says. Children generally outgrow croup as their airways widen.
Call the doctor: If you hear the stridor whistle when Baby is resting, he's breathing rapidly, and you can see the skin near his ribs and throat pull in with each breath (called retractions), call the M.D. His windpipe is closing. "If you've tried running the humidifier and using cool air and he's not getting better, seek medical attention," Dr. Beno advises. Your child may need steroids or epinephrine to reduce inflammation.