Of course, stopping is easier said than done, but new research says it is the only way to prevent your children being damaged by your addiction.
In fact, even if smokers try to limit their child's exposure to second-hand smoke, the dangers still exist.
In the latest research, children in Finland were measured for their exposure to passive smoking and whether their carotid arteries - the blood vessels that carry oxygen-rich blood to the head, brain and face - had become narrowed or blocked in adulthood.
The children were first studied in 1980 and 1983, and then again in 2001, 2007 and 2014.
This involved measuring the children's blood cotinine levels - a biomarker of passive smoke exposure.
The researchers found that 84 per cent of children from households where neither parent smoked had non-detectable cotinine levels in their samples.
However, only 62 per cent of children from households where one parent smoked and 43 per cent of children from households where both parents smoked had blood samples with non-detectable cotinine levels.
The risk of developing carotid plaque in adulthood was almost twice as high in children who had one or both parents who smoked, compared to children of non-smoking parents.
And the risk was elevated even if parents tried to limit their children's exposure.Children whose parents smoked but didn't limit exposure had almost twice the risk - and those fiull exposed had four times the risk, the study found.
Study author Dr Costan Magnussen, of the University of Turku, said in the journal Circulation: "Although we cannot confirm that children with a detectable blood cotinine in our study was a result of passive smoke exposure directly from their parents, we know that a child's primary source of passive smoke exposure occurs at home.
"For parents who are trying to quit smoking, they may be able to reduce some of the potential long-term risk for their children by actively reducing their children's exposure to secondhand smoke, by not smoking inside the home, car, or smoke well away from their children.
"However not smoking at all is by far the safest option."
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