What Is Croup? What Causes It?


Croup is a condition that irritates your baby’s upper airways and causes them to swell. As the airway below his vocal cords becomes narrow, your baby will find it hard to breathe. His breathing will be noisy and he’ll have a cough that sounds a lot like a high-pitched seal or dog bark. His voice will also sound raspy and hoarse, especially when he cries.

Croup is more common in the fall and early winter. It’s more common in boys than in girls. Babies between 3 months and 5 years of age are most at risk. The condition is contagious, especially in the first few days or until your child’s fever is gone.

What Causes It?

Most often, croup is caused by an infection. There are two types of this condition -- viral and spasmodic.

Viral croup is caused by any virus that infects the voice box (larynx) and windpipe (trachea). The virus that most often causes croup is parainfluenza. It might start out like a cold. But over time, your child will develop a “barky” cough. He also may make a high-pitched, wheezing sound in his lower airway when he breathes in. The croup sound in the upper airway is a harsh, loud sound known as “stridor.” There can be a low fever too.

Spasmodic croup comes on suddenly, often in the middle of the night. Your child might wake up gasping for air. He might also be hoarse, have stridor, and a barky cough. Fever isn’t common with spasmodic croup. Doctors believe it may be caused by an allergy or reflux from the stomach. That happens when contents from your baby’s stomach move back up into his esophagus.

No matter which type of croup it is, any time your child has difficulty breathing, retractions (when his skin pulls tight around his ribs), or stridor at rest, immediate medical attention is needed. Stridor when crying, agitated, or playing, or a barky cough is not an emergency. But if you have any concerns, go ahead and call your baby’s doctor.

WebMD Medical Reference Reviewed by Amita Shroff, MD on May 17, 2019



UpToDate: “Patient Education: Croup in Infants and Children (Beyond the Basics).”

KidsHealth: “Croup.”

American Academy of Pediatrics: “Croup and Your Young Child.”

Seattle Children’s.org: “Should Your Child See a Doctor? Croup.”

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