The role of water hardness in atopic dermatitis has received increasing research attention over the past decade. While causality is not definitively established, the evidence for a connection, particularly in infants, is accumulating.
What Is Hard Water?
Water hardness refers to the concentration of dissolved minerals, primarily calcium and magnesium, in tap water. Hard water is common in many parts of the United States and United Kingdom. Softened water has these minerals removed, typically by exchange with sodium or potassium.
The Proposed Mechanisms
Increased pH. Hard water has a higher pH than soft water. Healthy skin is acidic (pH 4.5–5.5), this acidity is critical for barrier function and antimicrobial defense. Repeated exposure to higher-pH water during bathing may disrupt the skin’s acid mantle.
Calcium and magnesium on the skin surface. These minerals deposit on the skin during bathing and interact with soap to form calcium soaps, which are irritating and difficult to rinse off, disrupting the skin barrier over time.
Increased S. aureus adhesion. Some research suggests hard water may increase the adhesion of Staphylococcus aureus, a key eczema aggravator, to skin cells.
What the Research Shows
Epidemiological studies have consistently found associations between water hardness and eczema prevalence, most strongly in infants and young children. A large UK study found a 56% increased risk of eczema in infants in the hardest water areas compared to the softest.
A pilot randomized controlled trial (SWET trial) found that installing water softeners in the homes of eczema patients improved skin scores, though the effect was modest and the study was small.
Practical Guidance
- Consider a water softener or shower filter if you live in a hard water area and have eczema-prone skin
- Rinse thoroughly after bathing to remove mineral deposits
- Use pH-balanced, fragrance-free cleansers rather than traditional soap
- Apply emollient immediately after bathing while skin is still slightly damp
NuLine’s eczema studies may offer treatments for better disease control.