The association between domestic hard water and eczema in adults from the UK Biobank cohort study.

concentrations, were associated with an increased prevalence of eczema in adults but not increased incidence. Ongoing efforts to reduce hard water exposure may have a beneficial effect in reducing the burden of eczema in adults. Further research is needed to explore area-level factors that may lead to eczema. What is already known about this topic? Hard water is formed when minerals are dissolved in water from filtration through sedimentary rocks. Several studies have reported a higher prevalence of eczema in areas with hard water. However, all studies on this topic have assessed this in infants and school-aged children, while this association has not been explored in adults. What does this study add? Our findings suggest that exposure to higher concentrations of domestic hard water is associated with an increase in eczema prevalence in adults aged 40-69 years. Ongoing efforts to reduce hard water exposure may have a beneficial effect in reducing eczema prevalence in adults.