Researchers at the Stockholm County Council's unit for Occupational and Environmental Medicine and the Institute of Environmental Medicine at Karolinska Institute monitored 4,000 children in Stockholm County from birth. Levels of traffic exhaust were measured at the site of the home.

The results show that the children who were exposed to high concentrations of pollutants ran a 60 per cent higher risk of suffering of persistent asthma symptoms.

Respiratory function was also adversely affected, and the children were much more likely to be allergic to airborne allergens, particularly pollen.

"Children who grow up in Stockholm are at greater risk of developing asthma, respiratory problems and pollen allergies if they live in areas where there are high concentrations of traffic pollution," the authors said in a statement.

"Not all children who live in areas with high levels of air pollution develop allergies. Whether they do or not is partly determined by genetic factors."