Scientists have found why colds make people with asthma more likely to have a severe and potentially fatal attack.
Colds are a major trigger of asthma attacks
UK researchers found there were low levels of proteins which should act as lung cells' first line of defence.
Writing in Nature Medicine, they say boosting levels of these proteins could protect people with asthma from having an attack because of a cold.
Experts welcomed the research, saying it offered a promising avenue for further work.
The researchers, from Imperial College and the Medical Research Council Centre in Allergic Mechanisms of Asthma, tested lung cells from people with and without asthma.
It was found that when the people with asthma were infected with a common cold virus, a rhinovirus, their lung cells produced half the usual levels of a type of interferon - a protein with antiviral properties generated by the immune system.
This lower the level of the antiviral protein, the more severe the asthma attack.
The team, led by Professor Sebastian Johnston, say uncovering this mechanism could lead to a new way of treating or preventing asthma attacks.
Inhalers could be used to get extra interferon directly to the lungs to help the immune system fight viral infection, they suggest.
It could be given either when the first symptoms of a cold appear, or even throughout winter as a preventative treatment.
Professor Johnston said: "The discovery of this mechanism could be of huge importance in how we treat asthma attacks.
"Delivery of the deficient interferons by inhalers could be an ideal way to treat and prevent severe attacks of asthma, potentially vastly improving the quality of life for many asthma patients."
The team are now carrying out trials to look at ways of treating patients with interferons, and trying to discover why they have too few.
Professor Tak Lee, director of the MRC - Asthma UK Centre in Allergic Mechanisms and Asthma, said: "This important finding paves the way for developing new approaches to prevention and treatment."
Asthma UK and the British Lung Foundation jointly funded the research.
Lyn Smurthwaite, of Asthma UK, said the research was an important step forward.
"Studies have shown that around 80% of asthma attacks in children and 60% of adults are caused by respiratory viruses.
"Yet no specific treatment is available and, on average, 198 people a day are admitted to hospital."
Helena Shovelton, chief executive of the British Lung Foundation, added: "The results will be of invaluable help in improving the treatment and care of people with asthma."