Maternal smoking during pregnancy leads to abnormal lung function in infancy that tracks through to later childhood and continues into adult life. This is associated with transient wheezing illnesses through early childhood. Both social and physiological factors are likely to predispose those exposed to passive smoke to become active smokers. Adult smokers demonstrate an increased decline of lung function with age. The effects of passive smoke exposure vary with genetic factors, gender, race and exposure to other pollutants. Exposure to environmental tobacco smoke and subsequent active smoking both aggravate symptoms and have a negative effect on lung function in those with asthma, (c) 2007 Elsevier Ltd. All rights reserved.