Influence of smoking on asthmatic symptoms and allergen sensitisation in early childhood

Background-Apart from heredity, several early life environmental factors ar e implicated in the development of childhood asthma. Maternal smoking is be lieved to increase asthmatic symptoms but its influence on the development of allergen sensitisation is debatable. Study design-A whole population birth cohort was reviewed at ages 1, 2, and 4 years. Of 1218 children seen at 4 years, 981 (80.5%) were skin prick tes ted with a battery of common food and aeroallergens. Smoking history was re corded at birth and updated at each follow up and its impact on the develop ment of asthma and allergen sensitisation in the children was assessed. Results-Two hundred and fifty mothers smoked during pregnancy (20.5%) and 3 07 (25.2%) after childbirth. Maternal smoking in pregnancy was associated w ith low birth weight (mean (SD): 3.3 (0.5) v 3.5 (0.5) kg; p<0.001). Smokin g mothers were more often from lower social classes (31.8% v 16%, p<0.001) and they breast fed their babies for a shorter duration (8.5 (11.4) v 16.6 (15.2) weeks; p<0.001). The difference in breast feeding duration was partl y due to a higher proportion of smoking mothers who never breast fed their babies. Although at age 2 years asthmatic symptoms were associated with exp osure to,maternal tobacco smoke (odds ratio 2.2, 95% confidence interval 1. 5 to 3.4; p<0.001), this association was lost by 4 years. However, maternal smoking was a significant risk factor in a subgroup of children with asthm atic symptoms but negative skin prick test. Maternal smoking did not increa se allergen sensitisation at age 4 years. No effect of paternal smoking on asthma was observed in the children.