What is Croup and What Causes It?

Croup is a common respiratory illness that affects babies and young children. While the symptoms can seem alarming, it is usually manageable with proper care. Farah Shahin, MD, a pediatrician with Stanford Medicine Children’s Health — Pediatrics in Menlo Park, shares the signs and symptoms of croup and the various treatment options.

What is croup?

According to Dr. Shahin, there are several viruses that can cause croup. The most common culprit is parainfluenza virus, but other viruses, such as COVID-19, RSV (also known as respiratory syncytial virus), and adenovirus, can also cause croup.

“Croup is a common childhood illness that causes swelling in the upper airway below the vocal cords, specifically the voice box and the windpipe,” Dr. Shahin says. “And that swelling causes the airway to become smaller in size and narrow and makes the breathing more noisy and makes it more difficult for the child to breathe.”

Croup tends to affect very young children, usually around 6 months to 3 years of age, though it can be seen up to age 6. “Young children are more likely to be affected by croup because their airways are smaller. And so a small amount of swelling can make it hard for them to breathe,” she says.

Like any illness, croup can spread easily, so children should stay home if they are sick. “It usually is spread by respiratory secretions or by coughing, sneezing. So while the child is sick, of course, they are highly contagious,” Dr. Shahin advises.

Symptoms of croup

Croup usually begins with a cough, a runny nose, and congestion like a typical cold. After a few days, it may progress to a hoarse voice and stridor: high-pitched wheezing along with the telltale cough that sounds like a seal or a barking dog. Many children will also have a fever.

“Usually, we notice that the symptoms are worse at night and can wake the child up from sleep in croup, as the swelling in the airways becomes worse,” Dr. Shahin explains. “In kids with croup, we notice that sometimes they can breathe faster than normal. And I always tell families that with croup, we notice that children have more severe symptoms or they feel worse when they are upset or crying or agitated. So I always recommend to parents and caregivers to keep their sick children with croup kind of quiet and calm.”

Treating croup

Dr. Shahin recommends treating croup like any other type of infection or cold and keeping your child hydrated by encouraging lots of fluids. She also suggests using a cool mist humidifier or running a hot shower and letting the child sit in the steamy bathroom (not directly in the hot water). Alternatively, you can open a window or take the child outside to breathe in cool, moist night air.

“Something that we often see is when children are coming into the clinic or urgent care at nighttime when the air outside is cool and moist, by the time the parents park their cars and walk into the clinic and the child breathes in that cool air, their symptoms actually can get better just because of that,” she says.

High fevers are common with croup, so over-the-counter medications such as acetaminophen and ibuprofen will help keep your child more comfortable and can help with their breathing, says Dr. Shahin. But steer clear of over-the-counter cough and cold medicines, as they have not been proven effective in young children.

She also recommends keeping an eye on the child overnight, when croup symptoms tend to be at their peak.

“Because croup symptoms tend to happen or be worse at night, I recommend for caregivers to stay close to their children, especially at night,” she says. “So, if the child begins to have any difficulty breathing or seems to need additional help, then the parent or the caregiver is right there.”

When to see a doctor

If you notice any of the following symptoms, Dr. Shahin suggests reaching out to your child’s pediatrician:

Your child is having a harder time breathing or is breathing faster than normal.

The skin and the muscles between the ribs and below the ribcage look like they are caving in or they’re being sucked in and out forcefully.

Your child is making a whistling sound, or stridor, when they are resting.

Your child is drooling or is having a hard time swallowing their saliva.

Your pediatrician can treat croup with a single dose of steroids. More severe cases may require a hospital stay and breathing treatments, according to Dr. Shahin.

Some croup symptoms warrant a visit to the emergency room. Call 911 or go to the nearest emergency room if your child has any of these symptoms:

Your child is turning blue or very pale—this could mean they are not getting enough oxygen.

Your child can’t speak or can’t cry—this could mean the swelling is blocking their airway.

Your child is lethargic or very sleepy and not responding to you or a caregiver.

Most kids recover from croup in a few days to a week. Remember, always trust your instincts, and seek help when needed for the well-being of your child.

To read more about croup, check out “Croup in Children,” or learn more about other common childhood illnesses: “Protecting Your Kids From Colds and Flu.”