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What is bronchiolitis?

Bronchiolitis is a lung infection that usually affects babies and very young children. The most common cause of bronchiolitis is a virus called respiratory syncytial virus or RSV.

Two different conditions

Bronchiolitis is a common infection in babies and young children. It should NOT be confused with a very rare condition called bronchiolitis obliterans (even though they share the same name).

Bronchiolitis and its causes.

How are babies and toddlers affected by bronchiolitis?

Bronchiolitis makes your baby cough and become breathless. This makes it hard for them to breathe and feed.

It usually starts with a runny or blocked nose, and over 2-3 days the small airways (bronchioles) in your baby's lungs get infected, inflamed and clogged up with mucus. 

In most cases, their breathing and feeding will get better within 5 days. Their cough might take longer to go – usually by around 3 weeks.

 “I didn’t realise my child had bronchiolitis”

Clare’s first child, Emma, was 11 months old when she developed bronchiolitis.

Read Clare’s story

Is my child at risk?

Bronchiolitis is common in babies and very small children up to 2 years old. It’s most common in babies between 3 and 6 months. 

Some babies and children are at greater risk of developing severe bronchiolitis:

  • premature babies
  • babies with existing heart or lung conditions
  • babies who have problems with their immune system from birth
  • children with Down’s syndrome.

Exposure to cigarette smoke makes it more likely for the baby to develop bronchiolitis, and more likely that the baby will develop a more severe illness.

What are the risks of passive smoking and vaping?

Your baby is most likely to have bronchiolitis over the winter - between October and March.

What causes bronchiolitis?

Bronchiolitis is caused by a virus. The most common virus that causes bronchiolitis is called respiratory syncytial virus or RSV. 

Not all babies infected with RSV will go on to develop bronchiolitis.

Generally speaking, children cope better with RSV as they get older.

Viruses are spread through the coughs or sneezes of someone who is infected. They can be breathed in from the air or picked up from a surface like skin, toys or door handles. You can help prevent your child from developing bronchiolitis, by taking steps to stop the spreading of viruses.

Next: what are the symptoms of bronchiolitis?

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Last medically reviewed: September 2019. Due for review: September 2022

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.