The causes of atopic dermatitis in childhood include dry skin and a disruption of the protective skin barrier. This can occur due to genetic predisposition. Environmental factors such as hard water and chlorine can also damage the protective skin barrier.

British and America researchers wanted to determine the degree to which hard water causes children to develop atopic dermatitis. They conducted a search in medical databases for all the studies available on the subject.

What was the study about?

The team, led by London-based researcher Zarif Jabbar-Lopez, investigated three questions:
What effect does high water hardness – i.e. a high level of calcium in the water – have

1. on the risk of developing atopic dermatitis (eczema)?
2. on the treatment of people who already have atopic dermatitis?
3. on the natural protective barrier of the skin?

How did the researchers conduct their study?

The researchers found over 5,000 studies and selected the best ones according to predefined quality criteria. Sixteen studies from 1996 to 2018 met these criteria and were further analysed. Jabbar-Lopez and his team summarised these studies in a meta-analysis.

What’s new?

Children growing up in areas with hard water are slightly more likely to develop atopic dermatitis than children in areas with soft water. This applies to children up to the end of primary school age. The results are based on seven studies with over 385,901 participants. In the studies, hard water was defined as water in the regions that contained more than 350 mg of calcium carbonate (CaCO³) per litre.

However, calcium is not the only problem. Laboratory tests indicate that the interaction with magnesium plays an important role. Magnesium supports the protective skin barrier. As long as water contains more magnesium than calcium, the calcium may even increase this positive effect. The ratio of calcium to magnesium should be less than 1.

Example: Dead Sea

Jabbar-Lopez gives an example of Dead Sea water, which has beneficial properties for the skin. It contains a lot of calcium (17,600 mg/l), but still significantly more magnesium (45,900 mg/l).

Water softeners

This could also explain why the use of water softeners (ion exchangers or filters) has little effect on the symptoms of atopic dermatitis, as data from two studies suggest. It is because the softeners remove not only calcium from the water but also magnesium.
Changes in symptoms were measured using different methods. The EASI score (Eczema Area and Severity Index) evaluates the size of atopic dermatitis lesions in four skin regions (head/neck, torso, arms, legs). They found that, before and after using the softened water, the size of the atopic dermatitis lesion did not change.
In the studies, however, the parents of children with atopic dermatitis were asked whether their symptoms had changed after the water was softened. The parents reported a slight reduction in symptoms. The POEM (Patient-oriented eczema measure) questionnaire was used for this assessment. Unlike EASI, it collects subjective data about symptoms, such as itching, sleep difficulties or dryness and scaling of the children’s skin.

Why is this important?

Jabbar-Lopez’s study is one of the biggest studies on water hardness and atopic dermatitis so far. It again provides evidence that there is an association between high water hardness and atopic dermatitis, especially in young children. However, even in this very large study analysis, the research team was not able to figure out exactly how hard water damages the skin barrier. Additional long-term studies are planned to investigate this.

Is my water hard?

In Germany, there are clear definitions of hard water: A new version of the Act on environmental compatibility of detergents and cleaning products  came into force on 5 May 2007. Section 9 of the law requires water supply companies to provide information on the hardness of the drinking water at least once a year.

• Hardness level – soft: less than 1.5 millimole of calcium carbonate per litre
• Hardness level – medium: 1.5 to 2.5 millimole of calcium carbonate per litre
• Hardness level – hard: more than 2.5 millimole of calcium carbonate per litre

Jabbar-Lopez’s study used milligrams instead of millimole per litre. But the conversion is simple: 1 mmol of calcium carbonate per litre of water weighs 100 mg.
Therefore 350 mg is equal to 3.5 mmol of calcium carbonate per litre.

Source

Jabbar-Lopez ZK et al. The effect of water hardness on atopic eczema, skin barrier function: A systematic review, meta-analysis. Clin Exp Allergy 2021;51(3):430-51.

Perkin MA et al. Association between domestic water hardness, chlorine, and atopic dermatitis risk in early life: A population-based cross-sectional study. J Allergy Clin lmmunol 2016;138(2):509-16

POEM. Patient-Oriented Eczema Measure as a tool for monitoring atopic eczema severity. University of Nottingham, UK