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Domestic water hardness and chlorine have been suggested as important risk factors for atopic dermatitis (AD). One recent study by researchers from Kings College London, United Kingdom, explored the potential associations between domestic water calcium carbonate (CaCO3) and chlorine concentrations in home water systems, damage to the skin's natural barrier, and incidences of AD in infancy.
Reviewed by Carsten Flohr, MD, and A Yasmine Kirkorian, MD
Domestic water hardness and chlorine have been suggested as important risk factors for atopic dermatitis (AD). One recent study by researchers from Kings College London, United Kingdom, explored the potential associations between domestic water calcium carbonate (CaCO3) and chlorine concentrations in home water systems, damage to the skin's natural barrier, and incidences of AD in infancy.1
Previous studies conducted in the UK, Japan, and Spain have suggested links between domestic water hardness and the risk of eczema in schoolchildren, but such association has not previously been studied in early infancy, claims the institution.
For this study, researchers recruited 1300 3-month-old infants from families across the UK, gathering information about levels of calcium carbonate and chlorine in their respective household water from local suppliers. The subjects were already participating in a study examining how to prevent food allergies in young children.
Researchers checked the infants for AD and assessed subjects’ skin barrier function by measuring transepidermal water loss (TEWL) on the skin of an unaffected forearm. They also screened for mutations in the filaggrin (FLG) gene, which codes for a key skin barrier protein. According to the National Institutes of Health's US National Library of Medicine, filaggrin plays a critical role in the skin's barrier function, bringing together structural proteins in the outermost skin cells to form tight bundles, and flattening and strengthening the cells to create a strong barrier. In addition, "processing of filaggrin proteins leads to production of molecules that are part of the skin's 'natural moisturizing factor,' which helps maintain hydration of the skin. These molecules also maintain the correct acid level (pH) of the skin, which is another important aspect of the barrier."
The UK study determined that living in an area with hard water was associated with up to an 87% increased risk of eczema at age 3 months, independent of the domestic water’s chlorine content. The risk tended to be higher in children with mutations in the FLG skin barrier gene, however the difference did not reach statistical significance.
Possible study limitations included the lack of information about the study subjects' exposure to swimming pools. Such exposure to water containing a considerably higher level of chlorine than domestic water could have had an added injurious impact on skin barrier function and risk of eczema.
“Our study builds on growing evidence of a link between exposure to hard water and the risk of developing eczema in childhood," states the study’s lead author Carsten Flohr, MD, from St. John’s Institute of Dermatology at King’s College London, United Kingdom, and Guy’s and St. Thomas’ NHS Foundation Trust. "It’s not yet clear whether calcium carbonate has a direct detrimental effect on the skin barrier, or whether other environmental factors directly related to water hardness, such as the water’s pH, may be responsible. Interactions between hardness and chlorine levels, other chemical water constituents, and the skin’s microflora may also play a role, and this warrants further research."
Flohr added, "We are about to launch a feasibility trial to assess whether installing a water softener in the homes of high-risk children around the time of birth may reduce the risk of eczema and whether reducing chlorine levels brings any additional benefits.”
A. Yasmine Kirkorian, MD, assistant professor of dermatology and pediatrics at Children's National Health System, George Washington University School of Medicine and Health Sciences, Washington, DC, finds this to be an interesting and credible study of infants, suggesting there likely is a link between hard water and AD risk.
“Their study had multiple strengths," Kirkorian notes. "First, they evaluated all of the children in person to diagnose and score the severity of their eczema. Other studies have relied on parental surveys which are not as objective or standardized. Second, they tested for mutations in the gene filaggrin, which is a known risk factor for eczema. Third, they evaluated children from all over the UK so they were able to compare areas with high rates of hard water to low rates of hard water,” she continues. “I think their data is intriguing regarding a possible link between hard water and eczema. They postulate that hard water might provoke or unmask eczema due to disruption of the skin barrier or possibly due to an interaction of the calcium in the water with filaggrin.”
Kirkorian also agrees with the study’s authors, however, that it’s probably too early to suggest that families install water softeners.
“As they note in their paper, a previous randomized trial of use of water softeners in the UK failed to show benefit. The authors hypothesized that this was because the Softened Water Eczema Trial used ion-exchange water softeners which removed the hard water, but didn't remove chlorine. The role of chlorine in exacerbation of eczema is unclear, but is interesting,” Kirkorian observes. “For now, I think it's too soon to recommend water softeners. However, if families have the ability and desire to purchase a water softener, I think we can cautiously support that intervention as an additional step beyond the critical dry skin care instructions we already provide. It remains to be seen whether we'll be recommending water softeners and chlorine filters one day.”
1. Perkin MR, Craven J, Logan K, et al; Enquiring About Tolerance Study Team. Association between domestic water hardness, chlorine, and atopic dermatitis risk in early life: a population-based cross-sectional study. J Allergy Clin Immunol. 2016;138(2):509-516.
Ms Hilton is a medical writer who has covered health and medicine for 25 years. She resides in Boca Raton, Florida. She has nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article.