Children may have an increased asthma risk if their father was exposed to smoking when he was growing up, a new study finds.

Researchers from the University of Melbourne have shown that smoking not only damages the health of the smoker and their children but also their grandchildren. Children are 59 percent more likely to develop asthma if their father was exposed to second-hand smoke when he was a child.

The findings are published in European Respiratory Journal. Using data from the Tasmanian Longitudinal Health Study (TAHS), one of the world’s largest and longest ongoing respiratory studies, the researchers examined data from 1689 children who grew up in Tasmania and their fathers and grandparents.

By looking at children who had developed asthma by the age of seven and whether their fathers grew up with parents who smoked when their sons were under fifteen years of age, the study examined the risk of developing asthma from second-hand smoke.

Mr Jiacheng Liu, from the University of Melbourne, said: ‘We found that the risk of non-allergic asthma in children increases by 59 per cent if their fathers were exposed to second-hand smoke in childhood, compared to children whose fathers were not exposed. The risk was even higher, at 72 per cent, if the fathers were exposed to second-hand smoke and went on to smoke themselves.’

Although the researchers are unsure of how this effect is passed through generations, Professor Shyamali Dharmage, who led the study, said the changes might occur due to epigenetic changes.

She explained: ‘This is where factors in our environment, such as tobacco smoke, interact with our genes to modify their expression. It’s possible that tobacco smoke is creating epigenetic changes in the cells that will go on to produce sperm when boys grow up. These changes can then be passed on to their children.’

The researchers hope that further investigation will highlight whether the increased risk of asthma in children persists into adult life and whether fathers exposed to second-hand smoke when they grew up pass on an increased risk of allergies or other lung diseases to their children.

In June, researchers at the University of Bristol said that the negative impact of smoking on mental health was 'no longer in doubt', and should be addressed by government policy.