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Is Water Hardness Correlated With Atopic Dermatitis?

There is an interaction between water hardness and filaggrin (FLG) gene mutations in the development of infantile atopic dermatitis (AD), a new study found. Researchers performed a longitudinal analysis of data from infants in the Enquiring About Tolerance (EAT) study, who were enrolled at 3 months and followed up until 36 months of age. They examined whether water hardness is associated with an increased risk of AD and skin barrier dysfunction in infants and to assess effect modification by FLG loss-of-function variants. Among the findings:

  • Of 1,303 infants enrolled in the study, 91.3% attending the final clinic visit, and 94.0% of participants’ families completed the 36-month questionnaire.
  • 58.1% of infants developed AD by 36 months.
  • There was no overall association between exposure to harder vs softer water.
  • There was an increased incidence of AD in infants with FLG mutations exposed to hard water.


Jabbar-Lopez ZK, et al. Longitudinal analysis of the effect of water hardness on atopic eczema: evidence for gene-environment interaction. [Published online ahead of print October 10, 2019]. Br J Dermatol. doi: 10.1111/bjd.18597.


It seems that almost every patient wonders if their water quality is contributing to AD. Is the water too hard or too soft? Would a change help? The usual recommendation has been that there's no good evidence that water quality in general makes any difference nor that installing a water softener will help. This study reinforces the understanding that in general water hardness isn't important with one exception. Infants with filaggrin mutations did have a higher likelihood of developing AD if exposed to hard water. — Joseph Fowler, Jr., MD, Clinical Professor of Dermatology, University of Louisville, KY