There is evidence that environmental factors are important for the development of eczema. Different mechanisms have been discussed in the literature, the best known of which is the hygiene hypothesis. However, epidemiological data give reason for questioning this hypothesis with regard to childhood eczema. We present results from two German birth cohort studies (LISAplus and GINIplus) concerning regional prevalence patterns of eczema and the association of eczema with day care center attendance and older siblings. Our findings are not in line with the hygiene hypothesis and question its validity with regard to eczema. It seems reasonable to assume that the effect of environmental factors is somehow disease-specific.