In short
Almost every child catches RSV before their second birthday, and in the youngest it inflames the smallest airways. Antibiotics do nothing, symptoms peak around days three to five, and how a baby feeds is the most useful thing to watch.
Emergency if: Pauses in breathing, grunting, the tummy sucking under the ribs, blue or grey skin, lips or tongue, or a baby who is floppy and will not wake — call emergency services now.
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01
What it is, and who gets it
Bronchiolitis is a chest infection affecting babies and children under two, most often around three to six months of age. A virus inflames the bronchioles — the smallest branches of the airway — and in a baby those passages are narrow enough that a little swelling and mucus makes breathing hard work.
It is not the same thing as bronchitis, which affects larger airways and people of any age. Respiratory syncytial virus, RSV, is the usual cause. RSV is extremely common and spreads easily in coughs and sneezes; almost all children catch it at least once before they turn two, and most cases are a bad cold rather than bronchiolitis.
02
How the illness runs
It begins like a cold — sneezing, a blocked or runny nose, a slightly raised temperature — and after a couple of days the chest becomes involved: a cough, faster breathing, wheezing or crackling sounds, difficulty feeding, and irritability. Symptoms after RSV exposure usually appear within about four to six days.
The shape of the illness is worth knowing in advance, because it tells you when to worry and when to hold your nerve. Symptoms are usually worst between days three and five. The cough then takes considerably longer to go than parents expect — often around three weeks.
03
Why antibiotics are not given
Bronchiolitis is viral, and antibiotics do not work against viruses. There is no specific treatment that shortens it. Inhalers, steroids and cough medicines have all been studied in bronchiolitis and none of them reliably helps, which is why a doctor who examines your baby and prescribes nothing is following the evidence rather than dismissing you.
Care is supportive and mostly practical: keep the baby upright while awake, which makes breathing easier, offer smaller feeds more often rather than full ones, and use paracetamol or ibuprofen at the appropriate age and dose if they are uncomfortable. Keep the air smoke-free, since breathing in cigarette smoke raises the risk of severe bronchiolitis.
04
Feeding is the measurement that matters
A baby working hard to breathe cannot easily suck and swallow at the same time, so feeding falls off before most other signs appear. That makes intake and wet nappies the most practical thing a parent can track, and the one doctors ask about first.
Seek advice if your baby is feeding much less than usual, or has had a dry nappy for twelve hours or more, or shows other signs of dehydration. Seek advice the same day for a baby under three months with a temperature of 38C or above, or a baby over three months with a temperature of 39C or above, and for any cold that is clearly getting worse rather than better.
05
Which babies are most at risk
Most babies ride this out at home. The ones who need closer watching are those under six months, babies born prematurely, and children with a weakened immune system or a long-term heart or lung condition. Around two to three of every hundred infants under three months are admitted to hospital with RSV each year.
Hospital care, when it is needed, is straightforward support rather than anything that shortens the illness: help with feeding or fluids, and extra oxygen while the illness passes. Knowing that in advance makes an admission far less alarming than it sounds.
06
Prevention, and the pauses to watch for
RSV is now preventable in the babies most likely to be harmed by it. A vaccine given later in pregnancy — from 28 weeks in some programmes, between 32 and 36 weeks in others — passes protection to the baby and reduces the risk of severe RSV through the first months of life. Where the mother was not vaccinated, many programmes offer babies an injection of protective antibodies before or during their first RSV season, and children at particular risk may be offered it again in a second season. Handwashing, keeping newborns away from anyone with a cold, and a smoke-free home do the rest.
In very young infants, RSV can show itself as irritability, reduced activity and pauses in breathing rather than as an obvious cough. Pauses in breathing are an emergency, as are grunting, the tummy sucking under the ribs, blue or grey skin, lips or tongue, and a baby who is floppy and will not stay awake.
When to act
Routine — see a doctor
A cold moving to the chest in a well baby who is still feeding and having wet nappies: upright when awake, smaller more frequent feeds, and expect the worst around days three to five.
Same-day — call promptly
Feeding much less than normal, a dry nappy for twelve hours or more, a cold that is getting worse, or a temperature of 38C or above under three months or 39C or above over three months.
Emergency — act now
Pauses in breathing, grunting, the tummy sucking under the ribs, blue or grey skin, lips or tongue, or a baby who is floppy and will not wake — call emergency services now.
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