Eczema and indoor environment: lessons from the International Study of Asthma and Allergies in Childhood (ISAAC) Phase 2

Numerous studies have reported a positive association between damp housing conditions and asthma, but little is known about indoor environmental exposures in relation to childhood eczema. We aimed to specifically investigate the effect of indoor mould and dampness on eczema risk in the International Study of Asthma and Allergies in Childhood (ISAAC).ISAAC Phase 2 is a cross-sectional study of 46 051 children aged 8-12 years from 20 countries. Information on demographics, eczema symptoms, and dampness was gathered with parental questionnaires. Children were examined for eczema and underwent skin prick testing. In a stratified subgroup, dust samples were collected to measure house dust mite exposure. Sex, maternal education, parental allergy, pet ownership, maternal smoking, having an older sibling, bedroom sharing, and cooking with fuels were explored as potential confounders or effect modifiers in logistic regression analysis.Current residential exposure to dampness and mould was significantly associated with flexural eczema in the previous year, with a stronger association seen in non-affluent than in affluent countries (adjusted odds ratio [OR] 1·96, 95% CI 1·62-2·37, vs 1·34, 1·18-1·51). Dampness and mould in the first year of life was also significantly associated with parent-reported eczema ever (1·94, 1·40-2·68, vs 1·43, 1·28-1·60). However, the association with flexural eczema on examination was not significant (0·93, 0·76-1·13). Risk estimates were similar in children positive and negative on skin prick testing, and were not appreciably altered by the effect modifiers, apart from parental allergic disease (parental allergies OR 1·35, 95% CI 1·18-1·54, vs no parental allergies 1·61, 1·37-1·90).These data suggest an association between damp housing conditions and childhood eczema symptoms, which may be causal. Further work is needed to elucidate possible mechanisms. Modification to home environment to reduce dampness and mould could be harnessed to improve or even prevent this common and debilitating condition.None.