Young children and babies forced to breathe second-hand cigarette smoke are more likely to be aggressive and anti-social as adults, according to new research.
Even brief periods of passive smoking have been found to cause lasting damage to the brains of children under 10, leading to negative changes in their behaviour.
Dr Linda Pagani and Dr Caroline Fitzpatrick, of the University of Montreal in Canada, said that children who came into contact with second-hand smoke are more to likely develop deviant behavioural characteristics.
Even small amounts of second-hand cigarette smoke can cause negative changes in behaviour when a child grows up (posed by models)
These finding were regardless of whether their mothers smoked while they were pregnant or their parents had a history of anti-social behaviour.
Dr Pagani said in the Journal of Epidemiology and Community Health: 'Exposure to this smoke at early childhood is particularly dangerous, as the child's brain is still developing.
'I looked at data that was collected from about 2,055 kids from their birth until ten years of age, including parent reports about second-hand smoke exposure and from teachers and children themselves about classroom behaviour.
'Those having been exposed to second-hand smoke, even temporarily, were much more likely to report themselves as being more aggressive by time they finished fourth grade (year five).'
The study is based on research that found 'sidestream' smoke can be more toxic than 'mainstream' smoke exhaled by the smoker.
Secondhand smoke comprises 85 per cent sidestream smoke, which comes straight from a burning cigarette and 15 per cent inhaled and then exhaled mainstream smoke.
Previous research has found 'sidestream' passive smoke from burning cigarettes is more toxic than smoke which has been inhaled then exhaled
Sidestream smoke is considered more toxic than mainstream smoke because it contains a higher concentration of many dispersed respirable pollutants over a longer exposure period.
Dr Pagani said: 'We know that the starvation of oxygen caused by smoke exposure in the developing central nervous system can cause low birth weight and slowed fetal brain growth.
'Environmental sources of tobacco smoke represent the most passive and preventable cause of disease and disability. This study suggests that the postnatal period is important for the prevention of impaired neurobehavioural development and makes the case for the promotion of an unpolluted domestic environment for children.'
Dr Pagani and Dr Fitzpatrick used existing data that health authorities in Quebec collect every year to uncover the link.
Dr Pagani said: 'Previous studies looking at groups of children have generally asked mothers whether they smoked or not, and how much at each follow-up, rather than asking whether someone smoked in the home where young children live and play.
'Furthermore, few studies have looked at anti-social behaviour in the parents and even fewer have investigated the subsequent influence of prolonged exposure to second hand smoke over the long term.
'None have taken into account the fact that disadvantaged families are less likely to participate in a long study like this one, which of course skews the statistics.'