A new genetic study has revealed that allergies are an outcome of asthma, not a cause of it.
Scientists have also found seven genes linked to the development of the ailment, which could lead to new treatments, reports the Sydney Morning Herald.
Researchers from Imperial College London and colleagues around the world carried out more than half a million genetic tests on 26,000 subjects.
They also found that adult-onset asthma and childhood asthma were different diseases.
But the head of respiratory and environmental epidemiology at the Woolcock Institute in Sydney, Guy Marks, said he did not think the study had definitively shown that allergies were a consequence of asthma, not the cause.
"That is the conclusion the authors have drawn but I would be a bit more cautious," he said.
He believed this type of research - including other genetic studies of asthma being conducted among Australians - might lead to better-targeted treatments and ways to prevent asthma in the first place.
The research highlighted that asthmatics were better off finding a medication that worked for them than trying to avoid potential allergens, , said Michele Goldman of the Asthma Foundation NSW.
The genes were found in a third of children with asthma. Some were involved in activating the immune system; others were linked to breathing. This means treatments could be designed to correct their function.
William Cookson, of Imperial College London, who co-ordinated the research, said: "Our study highlights targets for asthma therapies and suggests that therapies against these targets will be of use to many asthmatics."
The findings were published in The New England Journal of Medicine.