MedWire News: Parental smoking during childhood and personal cigarette smoking in teenage and early adult life lowers the risk for allergic sensitization in those with a family history of atopy, according to the results of a study from New Zealand.
Writing in the Journal of Allergy and Clinical Immunology, Robert Hancox (University of Otago, Dunedin) and colleagues explain that "the findings are consistent with the hypothesis that the immune-suppressant effects of cigarette smoke protect against atopy."
Avoiding exposure to cigarette smoke is often recommended to reduce the risk for allergic sensitization, particularly for children with a family history of atopic disease, the authors explain. But evidence for an effect of smoking on allergic sensitization is mixed.
Hancox and colleagues investigated the effect of passive smoking in childhood and active smoking in adolescence and adulthood on allergic sensitization in 972 participants in the Dunedin Multidisciplinary Health and Development Study, in which a prospective longitudinal population-based birth cohort was followed-up to age 32 years.
The authors obtained histories of parental atopic disease and smoking, and monitored personal smoking at multiple assessments between birth and age 32 years. Atopy was assessed by skin-prick tests (SPTs) for 11 common inhaled allergens at ages 13 and 32 years.
The team found that the children of atopic parents were less likely to have positive SPTs at 13 years if either parent smoked (odds ratio [OR]= 0.55), although the significance of the association was lost after adjusting for confounders.
Participants with atopic parents were also less likely to have positive SPTs between ages 13 and 32 years if they smoked themselves (OR=0.18), and this reduction in risk remained significant after adjusting for confounders.
The authors write: "We found that children who were exposed to parental smoking and those who took up cigarette smoking themselves had a lower incidence of atopy to a range of common inhaled allergens.
"These associations were found only in those with a parental history of asthma or hay fever."
They conclude: "The harmful effects of cigarette smoke are well known, and there are many reasons to avoid it.
"Our findings suggest that preventing allergic sensitization is not one of them."