The increased risks of respiratory disease in the children of smokers are most likely to be due to the adverse effects of parental smoking, rather than other confounding factors. Meta-analysis of published studies shows that the risks are greatest when both parents smoke, but are detectable even in families where only the father smokes. This suggests that postnatal (environmental) exposure is important. The independent effects of prenatal (intrauterine) and postnatal exposure to maternal smoking are difficult to disentangle.

Cook DG, Strachan DP. Health effects of passive smoking in children: summary of the evidence and recommendations for further resesarch. Thorax 1999;54:357-366