What is bronchiolitis?

Bronchiolitis is a type of chest infection that commonly affects children under 12 months of age. It occurs when the very small airways in the lungs, called the bronchioles, become inflamed and swell up.

Most cases of bronchiolitis start to get better on their own within a few days. However, some cases can be severe and need to be treated in hospital.


Bronchiolitis is a common chest infection that affects the small airways in the lungs, called bronchioles. This is different from bronchitis, which affects the larger airways in the lung called bronchi. Bronchiolitis is caused by a virus, most commonly the respiratory syncytial virus (RSV).

These infections can cause the small airways to become inflamed and produce more mucus than is normal. This leads to coughing and can cause difficulty breathing.

Bronchiolitis is contagious, which means it can be easily passed on to another person. Bronchiolitis can be spread by breathing in the droplets from an infected person's sneeze or cough.

Airway inflammation and mucus production during bronchiolitis. 


A thick, viscous liquid that is secreted for lubrication and to form a protective lining over certain tissues.

Respiratory syncytial virus

A common virus that causes mild cold-like symptoms in adults and healthy older children. It can cause more serious lung and airway infections in infants or people with serious illnesses.

Risk factors

Bronchiolitis commonly occurs in babies less than 12 months old, most often in infants under six months. Babies have an increased risk of developing severe bronchiolitis if they:

  • Were born prematurely;
  • Are less than six weeks old;
  • Have a weak immune system, or;
  • Have another medical condition, such as heart disease, a respiratory illness or a neurological condition

If bronchiolitis occurs in children over 12 months of age, asthma should be considered.

Respiratory illness

Any disease that affects the lungs and airways.

Signs and symptoms

At first the symptoms of bronchiolitis may appear similar to a common cold. This may include:

  • A runny or blocked nose;
  • A fever, and;
  • Coughing.

These symptoms may last one to two days, before becoming worse. As it progresses, the symptoms of bronchiolitis may include:

  • Fast breathing;
  • Wheezing;
  • Coughing, and;
  • Loss of appetite or difficulty feeding

Some cases of bronchiolitis can be very severe and require urgent medical attention or hospitalization. The signs of severe bronchiolitis include the baby having difficulty with feeding or reduced feeding, breathing very quickly, turning blue around the lips or fingers (which is a sign of not getting enough oxygen) and sucking in of the chest wall with breathing.


Breathing with a whistling or rattling sound in the chest.

Methods for diagnosis

To diagnose bronchiolitis, a doctor may ask questions about your baby's symptoms including feeding and if they have any other medical conditions. The doctor will use a stethoscope to listen to your baby's breathing and heartbeat. In particular, they will listen for crackling and wheezing sounds during breathing, which can be an indication of bronchiolitis.


Breathing with a whistling or rattling sound in the chest.

Types of treatment

Because bronchiolitis is usually caused by a virus, antibiotics will not help to clear the infection. Over-the-counter pain-relief medication, such as acetaminophen, may help to relieve some of the symptoms, such as fever. Other things that may help your baby's recovery include:

  • Allowing your baby to get plenty of rest;
  • Your baby might tire more easily with feeding, so keeping your baby well hydrated by offering smaller, more frequent feeds and;
  • Keeping your baby away from cigarette smoke and other substances that irritate the lungs.


Severe cases of bronchiolitis may need to be treated in hospital. Your baby may be admitted to hospital if they are having trouble breathing or are refusing food. While in hospital, their condition will be monitored closely to make sure they are getting enough oxygen. They may need to be given extra oxygen if they are having trouble breathing, or extra fluids if they have become dehydrated and are not feeding enough.

Potential complications

Some babies with bronchiolitis may also develop a secondary bacterial infection, which is a second infection that is caused by bacteria that develops after the viral infection.

Many children who develop bronchiolitis as a baby go on to develop asthma later in life. The link between the two conditions is not clear. It is not known whether bronchiolitis increases the risk of asthma, or whether children who develop asthma had an increased risk of developing bronchiolitis.


Most cases of bronchiolitis will get better on their own. Symptoms generally last a few days to a couple of weeks, although the cough may last up to a month. It generally does not result in any lasting health problems. Severe cases of bronchiolitis in which the baby has difficulty breathing or feeding and cases that are complicated by other medical conditions may need to be treated in hospital.


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