High levels of pollution in London's main shopping street could trigger an asthma attack, experts warn.
Christmas shoppers in Oxford Street could be at risk
Scientists at Imperial College London found the damaging effects of pollution on asthmatics were much greater in Oxford Street.
Levels of sooty particles from diesel vehicles were found to be five times higher than in Hyde Park.
The particles, known as PM10s, become trapped in the lungs and have links to respiratory problems and cancer.
Experts asked 60 asthmatics to walk at their normal pace in each location for two hours on separate occasions.
They found lung function was most affected after walking in Oxford Street for two hours. However, the adverse effects continued for 24 hours.
Dr James McCreanor, Specialist Registrar in Respiratory Medicine, who led the research, said it was one of the first studies to demonstrate the effects of pollution in a real-life situation.
"It shows that exposure to urban levels of diesel exhaust on Oxford Street causes a mild but marked temporary worsening of lung function, inflammation of the airways and increased symptoms among asthmatics.
"We are definitely not discouraging asthmatics from visiting Oxford Street, but to take care and increase their preventative medication if appropriate, before going out."