Experts say that outdoor smoking areas could be creating a new health hazard.
The new study, by researchers at Georgia University in the US, assessed the levels of a nicotine by-product, cotinine, in non-smokers exposed to second-hand smoke outdoors.
They found levels were 162 per cent greater than in those who were not exposed.
Amanda Sandford, from the anti-smoking charity Action on Smoking and Health (Ash), said:
"Although more research needs to be done to verify the findings of this initial study, it shows that further restrictions on smoking outdoors, such as smoke-free cordons around doorways, may be necessary to protect employees who are required to work in places where people are smoking."