What Is Croup? What Causes It?

Medically Reviewed by Carmelita Swiner, MD on November 10, 2022
3 min read

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



Most often, croup is caused by an infection. There are two types of this condition -- viral and spasmodic. It’s also called laryngotracheobronchitis.

Croup is more common in the fall and early winter. It’s more common in boys than in girls. Babies and children 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.

Viral croup is caused by any virus that infects the voice box (also called the larynx) and windpipe (the trachea). The virus that most often causes croup is parainfluenza. The symptoms are mild at first but get worse.

Spasmodic croup is rare. It comes on suddenly, often in the middle of the night. 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 their esophagus.

Other things can also cause a cough that sounds like croup. Your child may have breathed in something with fine particles, like powder or flour. A food allergy can cause their throat to swell closed. If you suspect a food allergy, call 911 right away. Other infections, including epiglottitis or bacterial tracheitis, have similar symptoms.

Croup might start out like a cold. But over time, your child will develop a “barky” cough. They also may make a high-pitched, wheezing sound in their lower airway when they breathe in. The croup sound in the upper airway is a harsh, loud sound known as “stridor.” There can be a low fever too.

Symptoms tend to be worse at night. Your baby might also have redness around their eyes, swollen lymph nodes, or a rash.

Any time your child has trouble breathing, retractions (when their skin pulls tight around their ribs), or stridor at rest, immediately call your doctor or 911. 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.

A doctor can usually diagnose croup by examining your child and listening to their symptoms. But they may need tests to rule out other causes. Your child’s doctor may:

  • Listen to their breathing
  • Look inside their throat
  • Ask about any recent illnesses or breathing problems
  • Take an X-ray to check for something stuck in their throat
  • Test their blood oxygen level

Most of the time, cases of croup are mild and can be treated at home. Try to soothe your child and keep them calm. Crying can make the coughing worse. Hold them upright.

Make sure your child has plenty to drink. Try over-the-counter medicines like acetaminophen and ibuprofen to treat a fever.

It might make them feel better to breathe steam or cool mist.

Call the doctor if your child:

  • Looks sick
  • Has trouble breathing
  • Isn’t speaking or drinking
  • Has noisy breathing even when not agitated

If they have to see the doctor, they may get a breathing treatment or a dose of steroids to bring down swelling in their throat and keep their airway open.

Show Sources


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.”

American Family Physician: “Croup: An Overview.”

Mayo Clinic: “Croup.”

American Academy of Family Physicians: “Croup.”

Merck Manual: “Croup.”

Johns Hopkins Medicine: “Croup.”

View privacy policy, copyright and trust info