What Is Croup? What Causes It?

Medically Reviewed by Jabeen Begum, MD on March 26, 2024
6 min read

Croup is an illness that babies and young children get. It irritates their upper airways and causes them to swell. As the airway around and below the vocal cords becomes narrow, your child will find it hard to breathe. Their breathing will be noisy or raspy and they’ll have a cough that sounds a lot like the high-pitched bark of a seal. Their voice may also sound hoarse. Crying can make their symptoms worse. Croup is most common in children under the age of 3 because they have smaller windpipes, which means swelling is more likely to affect their breathing. 

Most cases of croup are mild and you can usually treat it at home. But if your child is having a hard time breathing, they'll need medical care.

photo of croup anatomy



Croup is most common in the fall and early winter. It affects children assigned male at birth more often than children assigned female at birth. Babies and children between 3 months and 5 years of age are most likely to get croup. 

Normally, a virus causes the condition, but there are two other types of croup: spasmodic and bacterial.

Viral croup is caused by any virus that infects your child's voice box (larynx) and windpipe (trachea). Parainfluenza is the most common cause of viral croup. The symptoms are mild at first, but they get worse over 3-5 days.

Spasmodic croup is less common. 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 cause a cough that sounds like croup. Your child may have breathed in something with fine particles, like powder or flour. If they have an allergy, certain foods can also make their throat swell. If you suspect an allergy, you should call 911 right away.

Is croup contagious? 

Croup is very contagious, especially in the first 3 days after symptoms start or until your child’s fever is gone. Since a virus is usually the cause, it can spread through respiratory droplets that stay in the air after someone coughs or sneezes.

Can adults get croup?

Adults and older children can also get croup, but it’s rare. Since fully developed airways are larger, swelling is less likely to cause breathing troubles. If you do get croup as an adult, the symptoms can be stronger and you may need to see a doctor. 

Croup usually starts out like a cold, but over a few days your child may have a loud cough, raspy breathing, or sound hoarse when they speak. They might have a low fever too.

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

Some symptoms need emergency medical care, including:

  • Trouble breathing or swallowing 

  • Retractions (when their skin pulls in around their ribs)

  • Skin near their nose, mouth, or fingernails starts to turn blue (called cyanosis) 

Swelling that affects your baby’s ability to breathe or swallow might also lead to low oxygen levels or dehydration, both of which can be treated at a hospital. 

You might hear a vibrating sound in the upper airway, known as stridor, when your child is crying, agitated, or playing. This isn't an emergency unless it happens while they’re at rest. If you have any concerns, 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 X-rays to see inside their chest (rarely done)

Most of the time, croup is mild and you can treat it at home. Try to soothe your child and keep them calm since crying can make the coughing worse. Keep them upright as much as possible to make breathing easier. For kids older than 1, you can prop their heads up in bed using pillows. 

Make sure your child has plenty to drink. Clear, warm fluids like apple juice or lemonade can relax the vocal cords and loosen mucus. Ice pops might also help soothe their throat.

Try over-the-counter medicines like acetaminophen and ibuprofen to treat a fever, but avoid cough and cold medicines. 

It might make them feel better to breathe steam or cool mist. You can use a humidifier or run a hot shower, as long as you don’t let them near the water.  

Call the doctor if your child:

  • Has a fever that lasts more than 3 days 
  • Still has symptoms of croup after 1 week 
  • Has noisy breathing even when not agitated

Serious cases of croup may require hospitalization. Go to the emergency room if your child:

  • Has trouble breathing or swallowing
  • Can’t stop coughing 
  • Has retractions, where their skin is pulled tightly around their ribs 
  • Has blue-tinged skin

If your child has to see the doctor, they may get a breathing treatment or a dose of steroids. Steroids bring down swelling and help keep the airway open. Usually, your child only needs one dose that can be taken by mouth. It should start to work within 6 hours. A doctor may also give them a mist to inhale called epinephrine. The medication helps to reduce swelling but starts to work almost immediately. 

Other hospital treatments may include: 

  • Receiving humidified air or oxygen
  • IV fluids to treat dehydration
  • Keeping an eye on vital signs, including oxygen levels, breathing, and heart rate
  • In rare cases, the placement of a breathing tube 

Since croup spreads like the common cold, it’s hard to prevent. But there are things you can do to lessen your child’s odds of getting it. Hygiene is a good place to start: Wash hands regularly, and clean toys and surfaces. To slow the spread of germs, encourage your child to cover their mouth when they cough or sneeze, and get rid of dirty tissues right away. If they’re sick, keep them home from school or day care until they feel better. 

While there’s no vaccine to prevent croup, keeping your child’s vaccines up to date can keep them from getting more serious infections, like diphtheria and haemophilus influenzae, which can lead to a croup infection.

Croup usually isn’t serious and most cases can be treated at home. But if your child is having trouble breathing, see a doctor right away. Since croup spreads easily, practicing good hygiene can help keep your child safe and healthy.

What is the best thing to do for croup?

The best thing you can do is keep your child calm and comfortable. Also, make sure they drink a lot of liquids.

Will croup go away on its own?

Most cases of croup will clear up at home in 2 to 5 days, with symptoms lasting no more than 1 week. In more serious cases, symptoms might last as long as 2 weeks.

How long is croup contagious?

Your child will be contagious for 3 days after their symptoms start or until they no longer have a fever. 

Should I let my child sleep with croup?

Yes. Sleep helps fight infections, so you should let your child rest. If you want to monitor their breathing, you can sleep in the same room.