Toxic carbon monoxide gas, belched from car exhausts on city streets, could actually help ease the stress of urban living, according to scientists at Israel's Tel Aviv University.
A university website said research by Professor Itzhak Schnell showed that 36 healthy adults sent to pound Tel Aviv's pavements, ride its buses and shop in its street markets suffered less than expected from traffic fumes.
"The most surprising find of the study... was in looking at the levels of CO that the participants inhaled during their time in the city," said an English summary of the research published by the American Friends of Tel Aviv University.
"Not only were the levels much lower than the researchers predicted, approximately 1-15 parts per million every half hour, but the presence of the gas appeared to have a narcotic effect on the participants, counteracting the stress caused by noise and crowd density."
Carbon monoxide is an odourless, colourless and toxic gas, which can be fatal in high concentrations.
The Schnell study, part of a wider project to assess the impact of environmental stress on the human body, found that city life might not be such a health hazard as the researchers were expecting.
"Though participants exhibited rising stress levels throughout the day, CO had a mitigating influence, and extended exposure to the chemical had no lasting effects," it said.