Background: The increasing prevalence of eczema suggests the role of environmental factors triggering a genetic predisposition.
Objective: To analyze the effect of environmental exposures in early life and genetic predisposition on the development of eczema before age 3 years.
Methods: The Copenhagen Study on Asthma in Childhood is a prospective clinical study of a birth cohort of 411 children born of mothers with asthma. Eczema was diagnosed, treated, and monitored at the clinical research unit, and complete follow-up for the first 3 years of life was available for 356 children. Risk assessments included filaggrin loss-of-function mutation; parent's atopic disease; sex; social status; previous deliveries; third trimester complications and exposures; anthropometrics at birth; month of birth; duration solely breast-fed; introduction of egg, cow's milk, and fish; time spent in day care; cat and dog at home; feather pillow; nicotine in infant's hair; and temperature and humidity in bedroom.
Results: Eczema developed in 43.5% of the infants. Filaggrin mutation (odds ratio [OR], 3.20; 95% CI, 1.46-7.02; P = .004), mother's eczema (OR, 2.80; 95% CI, 1.70-4.63; P < .0001), and father's allergic rhinitis (OR, 1.91; 95% CI, 1.09-3.33; P = .02) were directly associated with risk of eczema. Risk of eczema was significantly reduced by birth length (OR per cm increase, 0.87; 95% CI, 0.78-0.97; P = .02), increased bedroom temperature (probably inverse causality; OR, 0.80; 95% CI, 0.66-0.97; P = .02), and dog living in the home (OR, 0.44; 95% CI, 0.23-0.87; P = .02).
Conclusions: Dog exposure reduced the risk of eczema, whereas short length at birth, filaggrin mutation, and parental atopy increased the risk of eczema by age 3 years.