According to ScienceDaily, researchers at Columbia University's Mailman School of Public Health found that increased cigarette use may explain the childhood asthma epidemic.

‘We have identified parallel increases in childhood asthma and cigarette use among adults during the past century in the United States,’ says author Renee D. Goodwin, PhD, MPH. ‘These parallel trends suggest that the increase in cigarette use may be a contributing factor to the rise in asthma among children during the same period through increased exposure to environmental tobacco smoke.’

Environmental tobacco smoke (ETS) is more harmful to children since they breathe more air and have smaller lungs. ETS actually has higher concentrations of some toxic substances (like carbon monoxide and carbon dioxide) than the smoke inhaled by smokers.

The risk for developing childhood asthma was 2.5 times greater in children with mothers who smoke more than 10 cigarettes per day indoors, compared to mothers who smoke fewer cigarettes or none at all. According to the Department of Health and Human Services, ETS increases a child's likelihood of developing asthma by 63 percent.

‘Previous data that show more recent higher rates of cigarette smoking among lower socioeconomic status segments of the population within the United States are consistent with our theory, since these are the most vulnerable segments of the population among whom rates of childhood asthma are currently the most concentrated,’ says Goodwin. ‘Although cigarette consumption has declined in some segments of the United States population since its peak around 1981, the consequences and health effects of the drastic increase in the mid-1980s are still affecting adults and children.’