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Medically reviewed by Last updated on May 21, 2024.

What is croup?

Harvard Health Publishing

Croup is a common respiratory illness in children that causes a change in breathing with a hoarse voice and a brassy, barking cough. Doctors sometimes call croup laryngotracheitis because it usually involves inflammation of the larynx (voice box) and trachea (windpipe).


Croup often is divided into two broad categories:  

Infectious Croup
Infectious croup is caused by an infection with a virus, bacterium or other germ. In the United States, most cases of croup are caused by a virus. These infections usually occur in the fall and winter when people spend more time indoors.  

Under these conditions, the virus spreads easily through coughing and sneezing. It also can travel on dirty hands and on things that have had contact with fluids from a sick person's nose or mouth. These include used tissues, toys, drinking glasses and eating utensils. 

Once the virus enters the body, it usually begins to attack the upper parts of the breathing system. For this reason, a child with croup may first complain of cold symptoms. These may include a runny nose or nasal congestion. The child also may have a low-grade fever or a mild sore throat.  

Later, the virus spreads farther down the throat. The linings of the voice box and windpipe become red, swollen, narrowed and irritated. This triggers hoarseness, a barking cough, and loud, raspy breathing (stridor). 

Spasmodic Croup
Spasmodic croup is very similar to infectious croup. It can be triggered by infection, but it isn't caused by infection. It tends to run in families, and may be triggered by an allergic reaction. 

Spasmodic croup tends to come on suddenly, without fever. Sometimes it can be hard to tell spasmodic croup from infectious croup. 

Infectious croup is most common in children younger than age six. Spasmodic croup usually affects children who are between three months and three years old. Before the age of three months, a child's risk of either type of croup is fairly low.

Symptoms of croup

The classic symptom of croup is a harsh, brassy cough that sounds like a seal's bark. This cough is often worse at night. And it usually occurs with hoarseness and loud, raspy breathing.  

Other symptoms vary, depending on whether the illness is infectious croup or spasmodic croup.

Infectious Croup

Children with infectious croup often have a low-grade fever and mild cold symptoms before a cough begins. In many cases, the sick child also has a history of being exposed to a family member, friend or classmate with a cough, runny nose or other signs of a respiratory infection. 

Most children with infectious croup are mildly ill and do not develop significant breathing problems.  

Among the few who do develop more severe forms of the illness, symptoms can include: 

Spasmodic Croup

A child with spasmodic croup often looks fairly healthy before coughing starts. Episodes of cough and loud, raspy breathing generally start without warning. They typically occur in the middle of the night.  

These symptoms often will pass if the child is carried into cool night air or taken into a steamy bathroom.  

Symptoms from spasmodic croup usually improve within a few hours. However, it is common for the symptoms to reappear several nights in a row.

Diagnosing croup

The doctor will review your child's symptoms. He or she will ask whether your child has been exposed to anyone with a cough or cold.  

The doctor also will review your child's immunizations for Haemophilus influenzae. Without these immunizations, this bacterium can cause epiglottitis. Epiglottis is a potentially life-threatening infection that can suddenly block the windpipe. Symptoms of epiglottitis can be similar to those of croup. 

Usually, your child's doctor can diagnose croup based on your child's history, symptoms and a physical examination.  

If your child's symptoms are severe or unusual, X-rays or other tests may be needed. These tests will check for more severe illnesses of the lungs or throat, including epiglottitis.  

Rarely, when a child has severe breathing difficulties, hospital care is necessary.

Treatment options

The following list of medications are related to or used in the treatment of this condition.

View more treatment options

Expected duration of croup

Symptoms of infectious croup usually go away within three to five days. However, some children have a mild cough that lasts a bit longer. 

Spasmodic croup tends to recur. The period between episodes is very variable.

Preventing croup

To help prevent viral infections that can cause croup: 

Treating croup

Your doctor probably will recommend actions to make breathing easier until the infection goes away.  

These include: 

Most children with croup have mild forms of the illness that can be treated at home. In particular, spasmodic croup often improves dramatically with only a cool mist vaporizer. 

In rare cases, a child with croup can develop severe breathing problems that must be treated in a hospital. There, the child may receive oxygen, epinephrine (a drug that opens the airways), corticosteroids and other measures to aid breathing. If there is any concern for a bacterial infection, the child will also be treated with antibiotics.

When to call a professional

If your child appears to have severe breathing problems, either call for emergency help immediately, or take your child to an emergency room.  

Some danger signs to watch for include: 


The majority of children with croup recover fully without complications.

Additional Info

Centers for Disease Control and Prevention (CDC)

National Institute of Allergy and Infectious Diseases (NIAID)

American Academy of Pediatrics (AAP)

American College of Chest Physicians (ACCP)

Learn more about Croup

Treatment options

Care guides

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.