Doctors have expressed doubts over the way they treat very young children who suffer wheezing attacks.
A study by British doctors has found the drugs commonly prescribed to pre-school children may have little effect.
The study of 200 children found those who received dummy pills fared just as well as those taking a five-day course of oral steroids.
Writing in The Lancet, the researchers said doctors should re-evaluate the way these children are treated.
Most cases of asthma are diagnosed in children between the ages of six and 16.
But a type of asthma also occurs in younger children. Doctors call it pre-school viral wheeze.
Children sometimes have wheezing attacks, leaving them gasping for breath.
Most young children who are diagnosed with the condition grow out of it and have no symptoms by the time they are six-years-old.
In the UK and the United States, doctors are advised to prescribe a five-day course of oral steroids to very young children who suffer from these wheeze attacks.
But previous studies have come up with conflicting conclusions over whether or not they are in fact effective.
Dr Abraham Oommen and colleagues from the University of Leicester decided to test the treatment themselves.
Their study involved 217 children, who were divided into two groups.
The parents of those in the first group were given a five-day course of oral steroids called prednisolone to give to the child if they suffered another wheeze attack. The parents of those in the second group received a placebo or dummy pill.
The doctors analysed the data for 120 children who went on to have another attack.
They found no difference between both groups. The severity of the attacks were similar for children in both groups and they were equally likely to end up in hospital.
"There is no clear benefit of a short course of parent-initiated oral prednisolone," the researchers wrote.
They said the current guidelines may need to be revised.
"This strategy may need re-evaluation for pre-school children with viral wheeze, since there are no clear benefits to balance potential risks."
Professor Martyn Partridge, chief medical advisor to the UK's National Asthma Campaign, said further studies are needed to confirm the findings.
"There are several other studies showing that in children in general, but not necessarily specifically in this age group, a very short course of steroids does help.
"Most doctors will therefore use their clinical judgment in each individual case."