Month of birth and prevalence of atopic dermatitis in schoolchildren: Dry skin in early infancy as a possible etiologic factor

Abstract

Background: Month of birth has been shown to affect later development of allergic diseases. Objective: We sought to evaluate the relationship between month of birth and the prevalence of atopic dermatitis (AD) in a large-scale general population of schoolchildren and to elucidate the possible mechanism for this relationship. Methods: Questionnaire data on the prevalence of allergic diseases were obtained for 33,725 schoolchildren aged 7 to 15 years. In a separate study the water-holding capacity of “uninvolved” skin was compared for children with and without AD. Results: We found striking differences in the prevalence of AD according to the month of birth (χ 2 = 34.9, P < .0001). Overall, those born in autumn showed the highest (7.5%), and those born in spring showed the lowest (5.5%), prevalence of AD. There was little or no such tendency for the prevalence of bronchial asthma (χ 2 = 17.2, P = .103) and allergic rhinitis (χ 2 = 24, P = .01). We found no statistical variation across birth month in the ratio of AD with no other allergic disease/total AD, indicating that this deviation was observed whatever the allergic predisposition of the subjects. In a separate study a significantly lower water-holding capacity of uninvolved skin was observed in children with AD even from early infancy. Conclusion: These findings lead us to speculate that the climate in early infancy affects the skin condition and that those born in autumn have dry skin in early infancy, which may ultimately result in a higher prevalence of AD among young schoolchildren. This might be at least one of the “nonallergic” etiologic factors of this complex disease. (J Allergy Clin Immunol 1999;103:1148-52.)