A Childhood Farm Environment Protects from Allergic Sensitization until Middle Age but Not from New-Onset Sensitization in Adulthood: A 15 Year Longitudinal Study.

Data are insufficient on the protective effect of a farm environment in childhood regarding sensitization in middle age and new-onset sensitization in adulthood. A skin prick test (SPT) and questionnaire data from the Northern Finland Birth Cohort 1966 study (NFBC66) were used to investigate sensitization at age 46 years related to childhood living environment. A subpopulation of 3409 participants was analyzed to study factors related to new-onset sensitization between ages of 31 and 46 years. Data on complete SPTs were available for 5373 cohort members at age 46. Professional farming by parents (odds ratio (OR) 0.54; 95% confidence interval (CI) 0.43-0.68) and keeping of farm animals (OR 0.53; 95% CI 0.43-0.66) in infancy were associated with a lower risk of sensitization at age 46. Sensitization (OR 0.58; 95% CI 0.47-0.72) and polysensitization (OR 0.43; 95% CI 0.32-0.57) were less common in those who lived in a rural area in infancy compared to a city area. The childhood living environment had no effect on new-onset sensitization between ages 31 and 46. We conclude that living on a farm or in a rural environment in childhood had a protective effect on sensitization even in middle age, but these factors did not protect from new-onset sensitization in adults.