Harmful air levels are reduced slightly but winding down a window does not lower them to a “safe level”, according to the findings.
The study involved a child-sized doll in a car seat with the latest smoke monitoring equipment attached at its mouth to record the effects of lighting up in the car.
The particles of tobacco poison were so high that they compared with the levels you would expect in a smoky pub before the smoking ban, researchers said.
NHS Greater Glasgow and Clyde (NHSGGC), who commissioned the study, has launched a campaign to persuade motorists who continue to smoke to make their cars tobacco-free.
Brenda Friel, NHSGGC senior health improvement officer, said: “No one would think twice about the dangers of taking a child into a smoke-filled environment yet many drivers don’t realise the harm that can be done.
“We know that second-hand smoke is very harmful but we wanted to understand in more detail the levels of risk attached to second-hand in smoke in cars with particular emphasis on children. The study has revealed some shocking facts.
“I am sure that there are many people who smoke in a car in which a child is travelling believe that opening the window is enough to protect them from any harmful effects. Our tests prove that this is not the case.”
The study was carried out by the Scottish Centre for Indoor Air, a research participation between the University of Aberdeen and the Institute of Occupational Medicine.