Dr. Ray Pawson of the University of Leeds in England and colleagues looked at the mixture of chemicals that make up secondhand smoke and its concentration in cars under different conditions involving volume, speed and ventilation and how long children were exposed in an automobile.
They examined the extent of difference between how secondhand smoke affects children compared with adults and they studied the health impact, which is hard to determine because of all the different chemicals and toxins a person is exposed to over a lifetime.
"The evidence does not show an absolute risk threshold because a range of environmental, biological and social factors contribute to the risk equation," Pawson says in a statement.
The evidence does, however, show conditional truths and the careful enunciation of each contributory condition is the task of public health science, the researchers say
The researchers say the results of their study, published in the Canadian Medical Association Journal, permit them to say that smoking in cars "generates fine particulate concentrations that are very rarely experienced in the realm of air-quality studies and that will thus constitute a significant health risk because exposure to smoking in cars is still commonplace, children are particularly susceptible and are at risk to further contamination if their parents are smokers."