Second-hand or passive smoke from tobacco is even sneakier than you might have thought, a new study suggests.

Let’s say you grow up in a household where nobody smokes. The air is clean and no one is entertaining you by blowing smoke rings.

But somehow you’ve ended up with smoking-induced breathing problems, including a higher risk of asthma, anyway.

How can this be?

According to University of Melbourne researchers, in a new study, you’re more likely to develop asthma as a child, if your grandfather was a smoker – even if you never met the croaky old blighter.

The troublesome link here is your dad, if he was passively exposed to granddad’s smoke as a small boy.

This would have increased your dad’s risk of developing asthma (or even emphysema) and somehow that risk has passed on to you – even if he never actually smoked.

The research was led by Jiachen Liu and Dr Dinh Bui from the Australian university.

It was based on data from the Tasmanian Longitudinal Health Study (TAHS), led by Professor Shyamali Dharmage.

TAHS began in 1968 and is one of the world’s largest and longest ongoing respiratory studies.

The researchers say they can’t be certain how this damage is passed on through generations, but Professor Dharmage said that they think it may be to do with epigenetic changes.

This is where factors in our environment, such as tobacco smoke, interact with our genes to modify their expression, she said.

“It’s possible that tobacco smoke is creating epigenetic changes in the cells that will go on to produce sperm when boys grow up,” Professor Dharmage said.

How did they reach this spooky conclusion?

The researchers looked at 1689 children who grew up in Tasmania, and also at their fathers and their paternal grandparents.

They compared data on whether the children had developed asthma by the age of seven years with data on whether the fathers grew up with parents who smoked when they were under the age of 15.

They also included data on whether the fathers were current or former smokers.

They 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.”

Dr Bui said the findings show how the damage caused by smoking can have an effect not only on smokers, but also their children and grandchildren.

“For men who were exposed to second-hand smoke as children, our study suggests that they can still lower the risk they pass on to their own children, if they avoid smoking,” he said.

The researchers will next investigate if the increased risk of asthma persists into adult life and whether fathers who were exposed to second-hand smoke as children pass on any increase in allergies or other lung diseases to their children.

What about mum?

The study was confined to male smokers, and the passive smoking exposure to their sons, and how that exposure affected the grandchildren.

The New Daily asked Dr Bui if there was any evidence that female smokers, their daughters and grandchildren may have similar outcomes?

He said that a few studies have suggested that if a mother is exposed to passive smoking when she was in utero (before she was born) it may also have an adverse effect on her children.

“It is noted that in a mother, exposure during her in-utero life is a critical window of vulnerability,” he said.

“For fathers, exposure during their post-natal years to puberty appears to be important.”

He said the new study had thrown up novel findings “that in males, the vulnerable window to the adverse impact of passive smoke exposure actually spans to their puberty”.