The effect of genetic and environmental factors on the prevalence of allergic disorders at the age of two years.

The effect of genetic and environmental factors on the prevalence of allergic disorders in early childhood was determined in a prospective follow-up study. Information was available on 1174 children at the age of 2 years. Two-hundred and seventy-five were considered to have an allergic disorder. The prevalence varied from 3.2% for rhinitis to 10.9% for asthma. At 2 years 60 children reacted positively on skin-prick test (SPT). Multivariate logistic regression analysis was used to obtain adjusted odds ratios (95% confidence interval) for each factor. For asthma, positive family history, male sex, low birth-weight, maternal smoking and season of birth were significant risk factors. For eczema, positive family history was the only significant risk factor. For rhinitis, lower socio-economic group and autumn birth were significant. Male sex and low birth-weight were significant for skin test positivity. Positive family history and low birth-weight were significant risk factors for any allergy. Low birth-weight was also a significant risk for skin test reactivity to house dust mite. Genetic and environmental factors have a profound effect on the development of allergic disorders in the first two years of life.