Atopic eczema and domestic water hardness

Background The environment plays an important part in the aetiology of atopic eczema, but specific causes are unknown. Exposure to hard water is thought to be a risk factor for eczema. We undertook an ecological study of the relation between domestic water hardness and the prevalence of eczema among Nottinghamshire schoolchildren. Methods Questionnaire details of 1-year period and lifetime prevalence of eczema were obtained from parents of 4141 randomly selected primary-school children and 3499 secondary-school children in southern Nottinghamshire. Geographical information systems (GIS) were used to link the geographical distribution of eczema prevalence with domestic water-hardness data (four categories). Adjustment was made for potential confounding by sex, age, socioeconomic status, and access to health care. Findings Among the primary-school children there was a significant direct relation between both 1-year period and lifetime prevalence of eczema and water hardness, both before and after adjustment for confounders. The 1-year period prevalence was 17·3% (261/1509) in the highest water-hardness category and 12·0% (94/786) in the lowest (adjusted odds ratio 1·54 [95% CI 1·19–1·99] p for trend <0·001). The corresponding values for lifetime prevalence were 25·4% (384/1509) and 21·2% (167/786; adjusted odds ratio 1·28 [1·04–1·58], p for trend=0·02). Eczema prevalence trends in the secondary-school population were not significant (adjusted odds ratio for highest compared with lowest hardness category for 1-year prevalence 1·03 [0·79–1·33], p for trend=0·46; for lifetime prevalence 0·99 [0·83–1·23], p for trend=0·93). Eczema prevalence in primary-school children increased in relation to chlorine content of water, but the trend across four chlorine-content categories was not independently significant after adjustment for confounders. Interpretation Exposure to hard water in the home may increase the risk of eczema in children of primary-school age.