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Striving for hard facts about water softening in atopic dermatitis


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By Warren R. Heymann, MD, FAAD
Aug. 18, 2021
Vol. 3, No. 33

With the success of dupilumab in managing atopic dermatitis (AD), and new agents on the horizon (IL-13 inhibitors lebrikizumab and tralokinumab; the IL-31 inhibitor nemolizumab; targeted anti IL-17, IL-22, and TSLP inhibitors; JAK inhibitors; and the PDE4 inhibitor rofumilast), it is easy to forget that simple maneuvers may help patients with AD even with advanced therapies.

When it comes to bathing, my guiding principles mirror those of Saini and Pensare: “1. Bathing is suggested for both treatment and maintenance; 2. No standard for frequency and duration is established; 3. Regular once-daily bathing with warm (not hot) water of short duration (5–10 minutes); 4. Limited use of nonsoap cleansers that are neutral to low pH, hypoallergenic, and fragrance free; 5. Generous and frequent application of moisturizers, applied soon after bathing, to improve skin hydration; 6. Soak and seal: soak skin in warm water for 15 minutes, light pat dry, and seal in moisturizer for severe AD.” (1)

One of the controversies over the past few decades is how hard water affects patients with AD. Does it aggravate the condition? Should water be softened for patients with AD? Will softening water halt the atopic march? This commentary addresses some recent literature on the topic.

Illustration for DWII on atopic dermatitis and water hardness
Illustration for DWII on atopic dermatitis and water hardness
Image from JAAD 2015; 73: 395-399.

AD is thought to be the first disease in the atopic march in development of other atopic manifestations, including food allergy, asthma, allergic rhinitis, and eosinophilic esophagitis. Strategies in halting the march have included emollients, breastfeeding, vitamin D, ultraviolet light, microbial exposures, probiotics, immunotherapy, and water hardness. (2)

Discussing water hardness makes me smile, because as a child I did not understand the concept when I heard the term. My pillow was soft, rocks were hard, and water was wet. What were people talking about? Hard water is defined as water containing divalent cations, notably calcium and magnesium at concentrations > 120 ppm. Water hardness varies by geography and mineral content of the water supply. According to the U.S. Geological Survey website, “You may have felt the effects of hard water, literally, the last time you washed your hands. Depending on the hardness of your water, after using soap to wash you may have felt like there was a film of residue left on your hands. In hard water, soap reacts with the calcium (which is relatively high in hard water) to form ‘soap scum.’ When using hard water, more soap or detergent is needed to get things clean, be it your hands, hair, or your laundry.” (3)

Since the 1990s, several studies have demonstrated an association between hard water and the incidence of AD. In the United Kingdom, this has been observed more so in primary school-aged children, but not those in secondary school. Similar findings were observed in Japanese and Spanish children in areas of hard water exposure. (4) Font-Ribara et al, however, in a cohort study found no correlation of water hardness and the incidence of eczema in children at 14 months to 4 years of age. (5)

These discrepancies could be explained by the study by Jabbar-Lopez et al in which 1,303 infants were assessed to determine whether water hardness is associated with AD and if these findings are associated with filaggrin (FLG) loss-of-function variants. In total, 761 (58·4%) developed AD by 36 months. There was no overall association between exposure to harder (> 257 mg L-1 CaCO3 ) vs. softer (≤ 257 mg L-1 CaCO3 ) water: adjusted hazard ratio (HR) 1.07. There was an increased incidence of AD in infants with FLG mutations exposed to hard water (adjusted HR 2.72), and statistically significant interactions between hard water plus FLG and both risk of AE and transepidermal water loss. This study demonstrated that although there was no association of AD to harder versus softer water, for infants with at least one FLG loss-of-function mutation exposure to harder water demonstrated a threefold increased risk of developing AD up to age 36 months, compared with infants with wild-type FLG exposed to softer water. (6) In an ongoing study, Jabber-Lopez et al will attempt to determine if use of an ion-exchange water softener can prevent AD in neonates. (7)

According to Walters et al, increased exposure to calcium may interfere with the normal epidermal calcium gradient, which is necessary for terminal differentiation of the stratum corneum and its barrier function. The authors demonstrated that baby cleansers can bind free calcium, thereby reducing the hardness effect of bathwater. (8)

It is intriguing to envision the day when a genetic profile can predict if water softening can prevent atopic dermatitis. For now, hard questions need to be addressed.

Point to Remember: There is conflicting literature about the role of hard water in atopic dermatitis — there may be a genetic influence. There is at least a theoretical benefit in trying water softeners in atopic patients. An ongoing trial will help determine if water softening can prevent atopic dermatitis and the subsequent atopic march.

Our expert’s viewpoint

Andrew C. Krakowski, MD, FAAD
Network Chair of Dermatology
Program Director for the Residency in Dermatology
St. Luke’s University Health Network
Easton, Pennsylvania

“Hard water, soft science?”

I tend to have a dry sense of humor, so I guess that is why Dr. Heymann asked me to dive right into this commentary. I do not want to dampen anyone’s spirits, but this current wave of focusing on hard water as an underlying cause of atopic dermatitis has left me all wet.

Submerging myself in the literature, I immediately got the feeling that the science behind this discussion is, at best, watered down and is, at worst, circling the drain. One example that should have landed someone in hot water is a 2017 article on the subject, published in the Journal of Investigative Dermatology, that was funded by Harvey Water Softeners, the makers of the very ion-exchange water softener being studied. This fact was noted by the authors as both a “Conflict of Interest” as well as an “Acknowledgment.” I felt so dirty after reading that at the end of the article that I had to take a bleach bath.

More recently, we have the report by Jabbar-Lopez et al that Dr. Heymann references above. The study seems well designed overall. However, as someone who treats atopic dermatitis on a daily basis, I feel some clarifications are necessary. For example, the authors use “≥5 baths a week” as a data point, but they fail to correlate specific frequency of bathing with clinical eczema severity. That is a confounding factor that could really muddy the water. There is a big difference, say, between two baths a day versus one bath a week. Were clinically severe subjects bathing excessively and stripping their skin of protective oils or were they “bath avoidant” and setting themselves up for colonization with Staph aureus? To me, the images from JAAD 2015; 73: 395-399 look a great deal like a kid who is drowning in Staph aureus and scratching himself into oblivion. I would like to know the skin swab status of these subjects going in and coming out of the study as that would likely be more clinically impactful (and treatable) than knowing hard water exposure status.

A similar issue surrounds the “moisturizer use ≥5 times a week” data point. Charles Chiang and Lawrence Eichenfield performed a small pilot study, in 2009, that sought to quantitatively assess the effect of combination bathing and moisturizing regimens on skin hydration in 5 pediatric subjects with atopic dermatitis and 5 subjects with healthy skin. (9) The authors found that bathing without application of moisturizer may actually compromise skin hydration. Somewhat surprisingly, they also discovered that bathing followed by moisturizer application provides modest hydration benefits — though less than that of simply applying moisturizer alone. So, knowing the details behind when and how subjects were applying their moisturizer (better yet, trying to control for this prospectively) could be really important.

Swimming just under the surface of this hard water exposure discussion is the notion that parents who have not yet purchased a water softener may actually be causing their children’s atopic dermatitis or, at least, failing to prevent it. I worry that the rising social media tide around this issue may lead to unnecessary feelings of parental inadequacy, guilt, and even bullying. This slope is certainly slippery when wet, and the financial implications are not inconsequential either. A quick look on Home Depot’s website demonstrates that water softener systems range in price from about $400 to $3,500. (10) Depending on what part you are talking about, the warranties range between 3 and 10 years. I would not want parents to take a bath on the purchase of an ion-exchange water softening system until we are sure it really matters. If we ever elucidate that hard water exposure is a real factor and a patient’s family cannot afford a water softening system, are the caregivers failing their child? Worse yet, what if the family makes the investment in a water softening system at the sacrifice of investing in a “3 times a day” supply of good moisturizer? I will take moisturizer every time based on my personal experience and the clinical data we have right now.

So, in summation, until a more vigorously derived verdict around hard water exposure comes in, let’s not throw the baby out with the bathwater!

  1. Saini S, Pansare M. New insights and treatments in atopic dermatitis. Pediatr Clin North Am 2019;66:1021-1033.

  2. Bawany F, Beck LA, Järvinen KM. Halting the march: Primary prevention of atopic dermatitis and food allergies. J Allergy Clin Immunol Pract 2020;8:860-875.

  3. https://www.usgs.gov/special-topic/water-science-school/science/hardness-water. Accessed August 16, 2020.

  4. Walters RM, Anim-Danso E, Amato SM, et al. Hard water softening effect of a baby cleanser. Clin Cosmet Investig Dermatol 2016;9:339-345.

  5. Font-Ribera L, Gracia-Lavedan E, Esplugues A, et al. Water hardness and eczema at 1 and 4 y of age in the INMA birth cohort. Environ Res 2015;142:579-585.

  6. Jabbar-Lopez ZK, Craven J, Logan K, et al. Longitudinal analysis of the effect of water hardness on atopic eczema: evidence for gene-environment interaction. Br J Dermatol. 2020;183(2):285-293

  7. Jabbar-Lopez ZK, Gurung N, Greenblatt D, et al. Protocol for an outcome assessor-blinded pilot randomised controlled trial of an ion-exchange water softener for the prevention of atopic eczema in neonates, with an embedded mechanistic study: The Softened Water for Eczema Prevention (SOFTER) trial. BMJ Open. 2019;9(8):e027168.

  8. Walters RM, Anim-Danso E, Amato SM, et al. Hard water softening effect of a baby cleanser. Clin Cosmet Investig Dermatol. 2016;9:339-345.

  9. Chiang C, Eichenfield LF. Quantitative assessment of combination bathing and moisturizing regimens on skin hydration in atopic dermatitis. Pediatr Dermatol. 2009 May-Jun;26(3):273-8. doi: 10.1111/j.1525-1470.2009.00911.x. PMID: 19706087; PMCID: PMC2762386.

  10. www.HomeDepot.com.



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