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.