Atopic dermatitis is a chronic skin
disorder in which the skin becomes dry, itchy and thickened. Even though it is very common in children,
its exact causes are not well-known.
Because water is a known skin irritant and the skin of infants are very
sensitive, it has been thought that hard water, that is water that contains
high calcium carbonate, may be a risk factor.
In this month’s issue of JACI, Engebretsen and colleagues investigate
whether early exposure to hard domestic water is associated with the prevalence
of atopic dermatitis (J Allergy Clin Immunol 2017; 139(5): 1568-1574).
To do this, they looked at the
Danish National Birth Cohort study which collected nearly 100,000 children born
between 1996 and 2002. Out of these, the
mothers of 55,092 children completed an interview at 6 and 18 months to get
more information on atopic dermatitis.
What the authors found was that hard water is associated with a higher
incidence of atopic dermatitis. This
effect was dose-dependent, and they attribute a 2% risk for atopic dermatitis
on hard domestic water. In addition,
they found that children born in autumn and winter had a higher incidence as
well. However, combined evaluation of these
two effects did not cause an even greater incidence on atopic dermatitis.
The reasons for this association
are unclear. The authors suggest that
hard water may change the acidity of skin and thus change the activity of skin
enzymes, or maybe that it requires more irritant soap for lather production
with hard water. It may even be that
hard water changes the growth of bacteria on the skin that may modulate risks
for atopic dermatitis. It also opens a
lot of other questions that have not yet been explored. Can water softening reduce the risk of
developing AD? What role do skin
moisturizers and other emollients have in preventing hard water-induced skin
damage? Does this effect extend to infants outside of Denmark and other Nordic
countries? Although these are all unanswered,
this study opens a new window for research and helps point the way for further
directions.
