Irish doctors claim they have found evidence that exposure to “second-hand smoke” in cars is damaging children’s health.

Their study isolated the effects of passive smoking in cars and found it gives rise to significant respiratory symptoms in children. Those exposed to cigarette smoke had a 35% increased risk of having wheeze symptoms and a 30% higher risk of hay fever.

“This paper is the first to isolate exposure in cars as distinct from the children smoking themselves and from exposure at home,” said Luke Clancy, the director general of the Research Institute for a Tobacco Free Society, and one of the study’s authors.

“We find second-hand smoke in cars does give rise to significant symptoms in these children. People say they’re only going down the road to school and ‘how do we know that it’s actually doing any harm?’. This says, ‘yes it is’.”

Clancy, a respiratory consultant, claims the findings support calls for a ban on smoking in cars similar to the workplace ban. Ash Ireland, an anti-smoking group of which Clancy is a board member, has been calling for such a ban for more than a year, pointing to similar legislation in Cyprus and some Australian, Canadian and American states and provinces. Clancy claims it would be too difficult to police a ban on smoking in private vehicles if children are present, and is instead demanding a blanket restriction.

“It should be banned outright in cars because you won’t be able to enforce it [if it only applies when children are present]. The reason the workplace ban works is because it is complete.”

The study, published in the European Respiratory Journal found that one in seven children in a nationally representative sample of 13- to 14-year-olds was exposed to passive cigarette smoke in cars. Second-hand smoke in a car is 23 times more toxic than in a house due to the enclosed space.

“Even if you open the window you don’t get rid of it all because the air that blows in doesn’t really drive it out,” said Clancy. “You can reduce it by ventilation but you can’t bring it down to none, and there is no safe level.

“The car window is more likely to be closed in Ireland because of the climate and you are more likely to get a lift when the weather is inclement.”

Girls were more likely to be exposed to second-hand smoke than boys. “We don’t know the reason for that because we didn’t anticipate it and didn’t ask the question, but it may be that girls tend to be given more lifts than boys, because parents don’t want them walking alone,” said Clancy.

Patrick Manning, the chairman of the medical committee of the Asthma Society of Ireland, and who was also involved in the research, said: “People tend to smoke a lot more in their cars to avoid the ban where they work. When children are exposed at home they can probably run out to the kitchen or somewhere. Most parents will smoke away from children.”

Asthma and bronchitis symptoms were also higher in the children exposed to second-hand smoke.

“Wheeze relates to the fact that the airways are quite narrow, so when the air is going through it is being pushed through a much narrower pipe,” said Manning. “It would be an abnormal finding [for teenagers to experience wheeze].”

Studies from America have identified that if children are exposed to either full or passive smoking, the level of lung capacity is reduced. “By the time they are in their early twenties they are probably at a much lower level of lung capacity [to] take them through life,” said Manning. “Lung capacity gradually wears off over 60 years or so. They are going to get problems earlier than you would expect.”

Clancy was one of six authors of the study. They used the International Study of Asthma and Allergies in Childhood and added an additional question regarding exposure in cars.

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