It's usually caused by the virus that is responsible for the common cold, but it can sometimes become something far more serious in a baby.
Around 3 per cent of all babies need hospital treatment for bronchiolitis - and doctors routinely give a powerful corticosteroid such as Decadron (dexamethasone) to stop the wheezing.
But when researchers tested the drug among 600 children admitted to 20 emergency departments for bronchiolitis, they found it was no better than a placebo, or sugar pill.
A single dose of 1 mg of oral dexamethasone per kilogram of the baby's weight was no more effective than the placebo in reducing the number of hospital admissions, or improving the baby's breathing after four hours, or improving the condition later on.
(Source: New England Journal of Medicine, 2007; 357: 331-9).