Farm environment in childhood prevents the development of allergies

Background A protective effect of infections in early life might explain the firmly reported finding of an inverse association between atopic disorders and large sibships. Objective To study the effect of childhood farm, rural non‐farm and urban environment, as well as family size and other factors on the occurrence of asthma, wheezing and atopic disorders up to young adulthood. Methods Data on lifetime prevalence of physician‐diagnosed asthma, allergic rhinitis and/or allergic conjunctivitis, atopic dermatitis, as well as self‐reported episodic wheezing from 10 667 Finnish first‐year university students aged 18–24 years were collected by a postal questionnaire. Associations of lifetime prevalence of the diseases with living on a farm, in a rural non‐farm and urban environment during childhood were estimated by logistic regression analysis. Adjustment was made for potential confounding by gender, parental atopy, parental education, number of older siblings, day care outside the home and passive smoking. Results The childhood farm environment independently reduced the risk for physician‐diagnosed allergic rhinitis and/or allergic conjunctivitis (adjusted odds ratio 0.63, 95% CI 0.50–0.79, P