Bronchiolitis is a common lower respiratory tract infection that affects babies and young children under 2 years old.
Most cases are mild and clear up within 2 to 3 weeks without the need for treatment, although some children have severe symptoms and need hospital treatment.
Further symptoms then usually develop over the next few days, including:
Most cases of bronchiolitis are not serious, but see your GP or call NHS 111 if:
A diagnosis of bronchiolitis is based on your child's symptoms and an examination of their breathing.
Bronchiolitis is caused by a virus known as the respiratory syncytial virus (RSV), which is spread through tiny droplets of liquid from the coughs or sneezes of someone who's infected.
The infection causes the smallest airways in the lungs (the bronchioles) to become infected and inflamed.
The inflammation reduces the amount of air entering the lungs, making it difficult to breathe.
Around 1 in 3 children in the UK will develop bronchiolitis during their first year of life. It most commonly affects babies between 3 and 6 months of age.
By the age of 2, almost all infants will have been infected with RSV and up to half will have had bronchiolitis.
Bronchiolitis is most widespread during the winter (from November to March). It's possible to get bronchiolitis more than once during the same season.
There's no medication to kill the virus that causes bronchiolitis, but the infection usually clears up within 2 weeks without the need for treatment.
Most children can be cared for at home in the same way that you'd treat a cold.
About 2 to 3% of babies who develop bronchiolitis during the first year of life will need to be admitted to hospital because they develop more serious symptoms, such as breathing difficulties.
This is more common in premature babies (born before week 37 of pregnancy) and those born with a heart or lung condition.
It's very difficult to prevent bronchiolitis, but there are steps you can take to reduce your child's risk of catching it and help prevent the virus spreading.
Some children who are at high risk of developing severe bronchiolitis may have monthly antibody injections, which help limit the severity of the infection.