How Hard and Soft Water Affects the Skin and Hair

Key Points

• Water contains varying levels of minerals which help to define its hardness
• Calcium and magnesium ions in water can react with the skin barrier and hair shaft causing irritation and damage
• Excess exposure to hard water may exacerbate dermatologic conditions such as xerosis and atopic dermatitis, and can weaken the hair shaft

Introduction

Skin and hair conditions can be caused by genetic, behavioral, and environmental factors. One environmental cause is the type of water we use for washing our skin and hair. The amount of minerals in water determines its hardness; our skin and hair can become irritated from interactions with these minerals. In this article, we will explore how water hardness can contribute to atopic dermatitis (AD), xerosis, and hair shaft damage.

What Makes Water “Hard” or “Soft”?

Have you ever wondered why your dishes have white markings after being washed in the dishwasher? Or why there are white deposits in your coffee maker? Both are a result of calcium residues from water.¹ Depending on where you live, water can have varying levels of dissolved minerals. As water moves through soil and rocks, it collects ions, including calcium and magnesium. While water consists of other minerals, these two divalent ions help to define a water’s “hardness”; the higher the calcium and magnesium levels, the harder the water.¹

The United States Geological Survey (USGS) sets standards for grading water hardness levels (Table 1).¹ When water is devoid of, or limited in, calcium carbonate (CaCO₃), it is considered “soft” (0-60 mg/L CaCO₃). Ultra-Pure Soft Water (UPSW) typically has <1 mg/L of CaCO₃ whereas Very Hard water contains more than 180 mg/L of CaCO₃.¹ While increased water hardness is not associated with significant health concerns, it can lead to skin and hair problems.

Our skin is in contact with water daily from hand washing to showering and may be vulnerable to the mineral contents in it. Water high in minerals can react with soaps to leave a film or residue on your skin.² This “soap scum” develops when divalent ions in tap water form an insoluble precipitate with fatty acids present in soap.² Researchers found that even after 180 seconds of washing with tap water, over 80% of fatty acids from soap remained in the stratum corneum of the skin compared to 90 seconds of washing with UPSW.² Thus, you may feel the need to use more soap to clean your hands or over-scrub your scalp when using hard water. Using hard water and excess soap may also reduce the natural oils on skin, leading to increased dryness and irritation.

How Does Water Hardness Impact Xerosis?

As we grow older, our skin becomes more susceptible to dryness. Keratinization— the process responsible for producing the protein keratin—is reduced.^3,4 Keratinocytes move from the stratum basale (bottom layer of the epidermis) to the stratum corneum (top layer of the epidermis) to become corneocytes, where they act in conjunction with lipids as a protective barrier for the skin. In aged skin, the lipid-protein membranes, intercellular junctions, and natural moisturizing factors (NMF) become diminished, leading to increased scaling, cracking, and wrinkling in the skin.⁴

A team of researchers from Japan conducted a study to assess the effects of UPSW on an elderly population.⁵ For twelve weeks, each of the study participants took a bath twice a day using either UPSW or tap water; the tap water contained a higher mineral content than the UPSW. Fifteen individuals were included in the final analysis and outcomes of interest included skin water content, trans-epidermal water loss (TEWL), and skin dryness. Participants’ skin in the UPSW group was more hydrated than those who bathed in tap water, although there was no difference in TEWL and skin dryness between the groups.⁵

A Danish retrospective cohort study also sought to determine if xerosis was increased in hard water areas among a group of blood donors. A pre-screen question included in a study survey assessed xerosis and water hardness data based on each participant’s municipality was obtained from the Geology Survey for Denmark and Greenland. The authors found that donors living in areas with medium to hard water levels (12-24 degrees of water hardness) had a higher probability of xerosis. This association was significant after excluding individuals with dermatitis, suggesting that water hardness and xerosis are associated independently from underlying dermatitis.⁶

Relationship Between Hard Water Use and Atopic Dermatitis?

A central feature of AD is disruption of the skin barrier. Both genetic and environmental factors contribute to AD development and exacerbation of the disease.

Some people with AD have a loss of function mutation in the filaggrin gene (FLG) contributing to skin barrier disruption. Filaggrin is a protein embedded in the stratum corneum layer that provides structural integrity along with keratin.⁷ When deficient, keratin filaments become disorganized, and epidermal homeostasis is disturbed.⁷ The presence of an FLG mutation had an additive effect on the sensitivity to hard water among those with AD.⁸ In a study of surfactant deposition following hard water exposure, hard water use resulted in significant surfactant deposition, specifically of the known irritant sodium lauryl sulfate (SLS). Those with AD and the FLG gene mutation were affected by SLS deposits to a greater extent than those with AD without a FLG mutation or those with healthy skin. TEWL was also found to be increased more in people with AD carrying the FLG mutation after washing with SLS in hard water, those with AD and the FLG mutation had increased TEWL, suggesting diminished skin barrier function as compared to people with AD without an FLG mutation.⁸ Therefore, using soft water may reduce water loss from the epidermis in those with a dysfunctional skin barrier due to AD associated with FLG mutations.

Additional studies demonstrated an association between AD and water hardness. One group conducted surveys that assessed lifetime occurrence and 1-year-period prevalence of eczema and obtained water supply information for water hardness readings based on household zones.⁹ The authors found an increased prevalence of eczema among primary-school aged children living in zones with higher total water hardness.⁹ This was attributable to calcium rather than magnesium content with an adjusted odds ratio of 1.29 for 1-year period prevalence of eczema in the highest versus lowest calcium categories (p=0.01, [1.00-1.66]).⁹

A randomized, double-blinded, placebo-controlled, crossover study comparing UPSW versus tap water baths in children with AD found a statistically significant improvement of out-in skin transparency (OIST).^10,11 OIST defines how easily substances and stimuli move across the stratum corneum; OIST is increased in those with AD and may exacerbate itching and dermatitis.¹¹ The authors also found that UPSW treatment improved pruritus and was associated with satisfaction with therapy.¹⁰

One pilot study evaluated the use of water filters in homes to reduce minerals that can be abrasive to skin. Pregnant women with a family history of atopy living in hard-water areas were given a domestic ion-exchange water softener to use at home, and the authors demonstrated feasibility of this approach.¹³ If future prevention studies show a reduced risk of AD in infants with this intervention, additional efforts at softening water may be justified.

How Does Hard Water Affect Our Hair?

Studies of hair structure suggest water hardness affects the hair shaft.

One group found that very hard water caused more abrasive texture, higher mineral deposits, and decreased thickness in women’s hair shafts when evaluated under a scanning electron microscope (SEM).¹⁴ Another study using the same protocol showed no difference in tensile strength or elasticity when comparing exposures.¹⁵ A study exposing hair to water according to real-life usage, however, found a statistically significant difference in magnesium deposition between hair treated with hard water versus bottled water but no significant differences in calcium deposition or hair damage as evaluated by SEM.¹⁶

More recently, a study comparing changes in baseline strength of hair samples after exposure to either deionized water or hard water did observe a statistically significant difference in reduced hair strength among men’s hair samples when treated with hard water versus deionized water.¹⁷ In fact, there was increased breakage following exposure to hard water. Another study comparing female hair samples washed with either hard water or distilled water found higher mineral deposition and decreased thickness in hair surface in the former group. However, this was not statistically significant.¹⁷ These two findings may be different because of varying methods used in the study.

Summary

Hard water may exacerbate xerosis, AD, and hair shaft problems. While more research is needed to better understand the effects of water hardness on the skin, investing in a water softener may promote hydrated and soap scum-free skin. Boiling water or using an ion-exchange water softener can deionize water and soften it, which may help those with xerosis and AD. 

Key Takeaways and Practical Tips

• Hard water consists of calcium and magnesium ions that may interact negatively with the skin barrier and weaken the hair shaft
• Bathing with soft water may help improve skin water content and reduce skin disruption and damage from reactions between minerals and lipid-proteins in the skin membrane
• Hair structure might be improved with use of deionized water or reducing how often one is exposed to hard water