Hard water, skin and hair: what the evidence says

Updated 20 Oct 2026

Hard water is not considered a health hazard, and the research on skin and hair is mixed. A pooled analysis of seven studies links hard water with somewhat higher odds of eczema in children, but its authors rate that evidence "very low" certainty. Trials of water softeners in children who already had eczema found no difference in severity compared with usual care. Small lab studies on hair strength disagree with each other.

What agencies say

"Hard water does not pose a health hazard," says the Maryland Geological Survey. Hardness is mostly dissolved calcium and magnesium; it stops soap from lathering and leaves white scale when water is heated (Maryland Geological Survey). EPA has no primary or secondary drinking water standard for hardness (Nebraska Extension).

Skin: the eczema studies

Most of the research is about atopic eczema (atopic dermatitis) in children.

Pooled observational data. A 2021 systematic review combined seven studies with 385,901 participants. Children exposed to harder water had higher odds of eczema (odds ratio 1.28), but the authors rated the certainty of that evidence "very low" (Jabbar-Lopez 2021).
Single cohorts disagree. In Denmark, among 52,950 children, eczema in the first 18 months was 5% more common for each 5-degree step up in water hardness on the German scale (Engebretsen 2017). A Spanish birth cohort of 1,638 children found no association at ages 1 and 4 (Font-Ribera 2015).
A possible mechanism. In a study of 80 people, skin washed with a detergent (sodium lauryl sulfate) in hard water kept more of it on the skin. This increased water loss through the skin and irritation, most of all in eczema patients carrying filaggrin (FLG) gene mutations. Ion-exchange softening reduced the effect. The authors said an intervention study was needed to test whether softening prevents eczema (Danby 2018).

What the softener trials found

Trial	Who	Result
SWET, UK, 2011	336 children aged 6 months to 16 years with moderate or severe eczema, in areas with at least 200 mg/L hardness	After 12 weeks, eczema improved 20% with a softener and 22% with usual care alone; the authors found no additional benefit from the softener (Thomas 2011)
SOFTER pilot, London, 2022	78 families in areas above 250 mg/L, given a softener or not before the baby was born	Visible eczema at 6 months in 33% with a softener and 48% without, but this pilot tested feasibility and ran no statistical tests (Jabbar-Lopez 2022)

In SWET, parents reported some improvements, but the researchers said these were likely response bias, because families knew whether they had a softener (Thomas 2011). The 2021 review pooled the two treatment trials and found no evidence that domestic softeners improve objective severity in established eczema, with "moderate" certainty (Jabbar-Lopez 2021). The SOFTER team concluded only that a full trial of softeners to prevent eczema is feasible (Jabbar-Lopez 2022), so whether softening from birth prevents it is not yet known.

Hair

The hair studies are small and measure strength in a lab:

15 volunteers' hair was soaked in hard water (212.5 ppm as calcium carbonate) or distilled water for 10 minutes every other day for 30 days. Tensile strength and elasticity did not differ (Srinivasan 2013).
Hair from 76 men, treated the same way for 3 months with much harder water (486.7 mg/L), lost significant tensile strength compared with deionized water (Luqman 2016). A follow-up with 70 men found the same (Luqman 2018).
Hair absorbs calcium and magnesium from tap water, chemically damaged hair the most. The minerals stiffened fibers, made combing easier, helped untreated hair hold a style and slightly reduced style hold in bleached hair (Evans 2011).

No study here looked at hair loss; the 2016 study describes its subject as weakening of hair, not hair loss (Luqman 2016).

Reading these results

Every softener in these studies was an ion-exchange (salt) softener. None tested a salt-free conditioner, which leaves the calcium and magnesium in the water; see salt vs salt-free softeners.
The hardness levels studied were high: SWET families lived in areas with at least 200 mg/L, about 12 grains per gallon, and the 2016 hair study used 486.7 mg/L, about 28 grains per gallon. Your water quality report gives your level; see how to read your water quality report.
If you do soften, size the unit for your hardness with what size water softener do I need.