Young children living near a major road suffer more coughing attacks, research has found.
Exhaust fumes damage the lungs
Scientists at Leicester University found the closer children lived to a main road, the more likely they were to have a cough symptoms.
For each 100m, the day-time coughing rate went up by 3%, and the rate of dry night-time cough by 2%.
The research, on children aged one to five years, was presented at a meeting of the British Thoracic Society.
The researchers say a number of pollutants could cause the problem, including nitrogen oxide, ozone and particulates - microscopic particles produced primarily by diesel engines.
The smaller particulates are thought to be particularly dangerous because they are so tiny that they can penetrate deep into a child's lungs, settling in areas where the body's natural clearance mechanisms can't remove them, and triggering tissue damage.
Dr Jonathan Grigg, from the Leicester University Children's Asthma Centre, said previous research had linked exposure to traffic fumes to wheezing in older children, but not coughing in children who were so young.
He said: "Our study has provided clear evidence that particles from vehicles are a significant irritant on the airways of young children."
He said the effect on individual children was probably quite small, but it was unclear whether developing a cough so young could lead to respiratory problems later in life.
He said the primary take home message was that road traffic experts should place greater emphasis on health effects when planning new roads.
Dr John Harvey, of the British Thoracic Society, said: "It is essential that we work together to limit the impact of road traffic pollution on the health of young children's lungs and to support research into the mechanics of this relationship."
Exposure to traffic fumes has also been linked to fertility problems.