Abstract
Introduction: Cigarette smoking has immunosuppressant effects. Whether smoking affects allergic sensitisation remains uncertain. We studied the association between smoking and the development of atopy in a population-based cohort.
Methods: Skin-prick tests for 11 allergens were performed at ages 13 and 32. A weal diameter at least 2mm greater than negative control to at least one allergen was considered positive. Smoking history was recorded throughout teenage and early adult life.
Results: Of those who had negative skin-prick tests at age 13, 69/182 (38%) never smokers had positive skin-prick tests at age 32 compared to 54/194 (28%) amongst those who had smoked at sometime between the two ages (p=0.04). The incidence of atopy between 13 and 32 tended to be lower in those who were current (25%) than ex-smokers (33%) at age 32. Among those who had positive skin tests at age 13, there was no difference in the proportions of smokers (94%) and never smokers (94%) that remained atopic at 32. Those who were atopic at age 13 were no less likely to take up smoking than those who were not (48% vs 52%, p=0.36). Those with a parental history of asthma or hay fever had similar rates of smoking to those who didn't (51% vs 50%, p=0.85).
Conclusions: Smoking is associated with a reduced incidence of atopy in adolescence and early adulthood. There was no evidence that teenagers who were atopic, or at risk of atopy, were more likely to avoid smoking and the association is unlikely to be due to ²reverse causation². The findings provide evidence that smoking directly or indirectly influences immune function to inhibit allergic sensitisation. However, smoking did not reverse atopic sensitisation that had developed in childhood.