Those children exposed to passive smoking on a daily basis and for many hours are the most vulnerable facing over treble (3.63) the risk of those who grew up in smoke-free environments.
Children experiencing passive smoke a few times a week are one and a half (1.45) times more likely to develop lung cancer, and those exposed daily but not for many hours faced twice (2.08) the risk.
In one of the most comprehensive studies into passive smoking of its kind, researchers looked at 303,020 people across Europe who had never smoked, or had stopped smoking by at least ten years. Within this group, 123,479 provided information on exposure to passive smoke, and researchers followed these participants' progress for an average of seven years.
Of those who had known exposure to passive smoke (but were not smokers themselves), 97 had developed lung cancer, 20 more had upper respiratory cancers such as cancer of the larynx, and 14 died from chronic obstructive pulmonary disease during the seven follow-up years.
Former smokers faced up to twice the risk of respiratory diseases from passive smoke than those who'd never smoked. This may be because their lungs are already damaged, making them more at risk to the effects of environmental tobacco smoke, say the researchers.
This study significantly reinforces previous research into the cancerous effects of passive smoke, the authors conclude.