Water hardness and a possible genetic link with eczema in children

Previous studies have found a possible link between the risk of children developing atopic eczema, and hardness of the water used at home. The harder the water (containing more calcium), the more children seemed to develop eczema. Yet a study in children with eczema using water softeners to reduce water hardness had shown no difference in eczema severity. In this UK study, data was used from 1303 children who had participated in the Enquiring About Tolerance (EAT) study. The aim of that study was to investigate if food allergies can be prevented. The available data of these children was quite comprehensive and included if they developed eczema between 3 months and 36 months of age, and if they had a genetic mutation of their skin ‐ specifically, a mutation of the gene that is responsible for producing the protein filaggrin in the skin. Filaggrin is necessary for a smooth, hydrated and healthy skin. What the researchers did was add to all these data the hardness of the water the children had used at home for bathing and washing, based on their postal code. They then divided these children into two groups: one half had used softer water (257 milligrams or less of calcium carbonate per litre), and the other had used harder water (258 or more milligrams). Overall the researchers found no significant difference between the two groups in parent‐reported atopic eczema by 36 months of age. But when they took the filaggrin mutation into account, they found a big difference. Children who had a mutation of that filaggrin gene and who were exposed to harder water, had about a threefold increased risk of developing eczema than those without the mutation and who were exposed to softer water. The researchers conclude therefore that in children there seems to be a link between having a filaggrin mutation, being exposed to harder water and developing eczema. Linked Article:   Jabbar‐Lopez et al. Br J Dermatol 2020; 183 :285–293.