Ash Scotland tested children aged one to five from 54 smoking households in Aberdeenshire for nicotine exposure and found all but one had very high concentrations of nicotine in their saliva. Two children aged three and five were exposed to pollution 50 times greater than peak time traffic in Edinburgh city centre.
One mother smoked in every room apart from the children's bedrooms and also in the car, despite one of her children having asthma. Researchers found air pollution nearly 20 times greater than the World Health Organisation's recommended limit in her flat.
Dr Sean Semple, of Aberdeen University, who analysed the results, said: "Over 85% of the fine particles and hazardous chemicals in second-hand smoke are invisible."
Sheila Duffy, chief executive of Ash Scotland, said: "We know that smoking parents want to protect their children. That is why we encourage them to do their smoking outside, and make their home and car entirely smoke-free."