Steroids are used to ease symptoms of wheezing
Giving younger children hospitalised with wheezing high doses of steroids may not help them, a study suggests.
This approach - widely used in the UK and elsewhere - produced no benefits in a UK trial of more than 700 pre-school children.
A specialist said that guidelines might be reconsidered in the light of the New England Journal of Medicine research.
However, he said steroids could be "lifesavers" for older children and adults.
Steroids help suppress the inflammation which causes the airways to narrow in people with asthma.
Many long-term asthma medications contain steroids, but if the asthma suddenly worsens doctors may give a short course of pills or medicine to try to get it back under control.
The study, led by Professor Jonathan Grigg at the Barts and The London Medical School, does not challenge this tactic in older children and adults with asthma, but questions whether much younger children should be treated the same way, as many of the children might have asthma symptoms, but their wheezing is due to viral infection rather than asthma itself.
He followed the progress of children hospitalised with severe wheezing symptoms, half of whom were given steroids, while the other half got a "dummy" medication containing none.
He found that the children who received steroids spent just as long in hospital, needed the same amount of other treatments, and were just as well as those who got the "dummy" drugs.
Professor Grigg said: "Wheeze in young children is, in many ways, very different from wheeze in older children and adults.
"We urgently need high quality research to investigate how best to treat young children who only wheeze in response to viral infections and to find ways of identifying the minority of wheezy pre-school children who will go on to develop asthma."
Dr Mike Thomas, from Asthma UK, which funded the study, said that the finding could have "important implications" for doctors.
He said: "Young children who only get wheezy when they have a cold or viral chest infection, but can breathe normally at other times,are likely to grown out of their tendency to wheeze by their teenage years.
"It is important that we stop relying on a 'one solution fits all' which means that these young children are taking steroids unnecessarily."
Dr Iolo Doull,a consultant in paediatric respiratory medicine at the University Hospital of Wales in Cardiff, and secretary of the British Paediatric Respiratory Society, praised the study, but said that any decision to change the way that steroids were prescribed to young children would need careful consideration.
He said: "We know that in older children, and adults, these drugs can be highly effective - even lifesavers on occasion.
"There isn't a huge downside to giving short courses of steroids like this, but obviously you don't want to give any drug unnecessarily, and this research offers a very powerful argument."