Causes of bronchiolitis in infants

Viruses spread through coughs, sneezes, hands, and close contact. An infection may begin with a runny nose, then move into the smaller airways. Swelling and mucus narrow these passages, which can lead to cough, wheezing, faster breathing, and difficulty feeding. Learn more about [Bronchiolitis](/conditions/bronchiolitis/).

The cause is not usually a food allergy or cold air. Several respiratory viruses can produce a similar pattern, so symptoms alone may not identify the exact virus. Antibiotics do not treat a viral cause unless a clinician finds a separate bacterial infection.

Wash hands before touching the baby, avoid close contact with people who are ill, and keep smoke and vaping away from the home. Clean frequently touched surfaces and do not share bottles, cups, towels, or pacifiers between children. Offer feeds as advised and observe breathing, alertness, and wet nappies.

Do not use leftover antibiotics, cough medicines, or unprescribed inhaled treatments. A clinician can decide whether examination, monitoring, or additional support is needed.

Get urgent help when an infant has marked chest pulling, grunting, pauses in breathing, blue or grey lips, unusual limpness, or cannot keep feeds down. Contact a clinician promptly for worsening cough, wheezing, fever, fewer wet nappies, or a baby who is much sleepier than usual. See [Cough](/symptoms/cough/), [Fever](/symptoms/fever/), and [Wheezing](/symptoms/wheezing/) for symptom context.

Ask which cause is most likely, whether the baby needs testing, how to protect siblings, and what changes should trigger immediate help. Mention prematurity, heart or lung conditions, immune problems, feeding changes, and the number of wet nappies.