Could Softening Your Water Cure Childhood Eczema?
Exploring the groundbreaking SWET trial that investigated whether water softeners could improve eczema symptoms in children living in hard water areas.
For parents of children with moderate to severe eczema, the quest for relief often leads down countless avenues. Among the most persistent suggestions is one that seems to make intuitive sense: install a water softener. The anecdotal evidence appears compelling—families who swear their children's eczema improved dramatically after switching to softened water. Dermatologists noticed that eczema prevalence seemed higher in areas with hard water. But was this connection real or merely coincidence?
In England, particularly the southern regions, most households receive very hard water (>250 mg/L calcium carbonate) through their domestic supply 9 .
The Softened Water Eczema Trial (SWET) emerged as the definitive scientific investigation to answer this pressing question.
In one of the most ambitious eczema studies ever conducted, researchers embarked on a mission to determine once and for all whether ion-exchange water softeners could truly improve eczema symptoms in children. The results would challenge popular beliefs and reshape our understanding of environmental factors in eczema management.
Before examining the SWET trial itself, it's important to understand the theoretical connection between water hardness and eczema. Hard water contains high levels of dissolved minerals, primarily calcium and magnesium carbonate, acquired as water percolates through rock formations.
Several mechanisms have been proposed for how hard water might exacerbate eczema:
Hard water reduces the lathering ability of soaps and detergents, potentially leading to more residue left on skin and clothes after washing. These deposits can irritate sensitive eczematous skin .
Research suggests hard water may raise the skin's surface pH and directly damage the skin barrier, our primary defense against environmental threats 6 .
Calcium ions in hard water might disrupt normal skin cell function and barrier repair processes 9 .
By compromising the skin barrier, hard water could potentially allow easier entry for allergens and irritants 4 .
The SWET trial was a multicentre, randomised controlled trial conducted across England in hard water areas including Nottingham, Leicester, Lincoln, North London, Cambridge, Portsmouth, and the Isle of Wight 3 . The study employed an "observer-blind" design, meaning the research nurses assessing the children's eczema severity didn't know which treatment group each child belonged to—a crucial feature that minimized assessment bias.
336 children aged between 6 months and 16 years
Diagnosed with moderate to severe eczema
Lived in homes with water hardness ≥200 mg/L calcium carbonate 1
Participants were randomly assigned to one of two groups:
Received installation of an ion-exchange water softener plus usual eczema care for 12 weeks
Continued with usual eczema care alone for 12 weeks
Followed by a 4-week observational period where the water softeners were switched off/removed from Group A homes and installed in Group B homes 1 .
The ion-exchange water softeners were installed to soften all water in the home except for one kitchen tap that supplied mains drinking water . This ensured participants were exposed to softened water for bathing and clothes washing while continuing to drink regular mains water.
The researchers employed multiple assessment methods to capture different dimensions of eczema severity:
Change in eczema severity as measured by the Six Area, Six Sign Atopic Dermatitis (SASSAD) score at 12 weeks compared to baseline. This objective scale was completed by blinded research nurses who examined six specific body areas for six signs of eczema 1 .
When the results were analyzed, the findings challenged popular belief. The mean change in SASSAD score at 12 weeks was virtually identical between both groups: -5.0 (20% improvement) for the water softener group versus -5.7 (22% improvement) for the usual care group 4 .
| Group | Mean Change in SASSAD Score | Percentage Improvement | Statistical Significance |
|---|---|---|---|
| Water Softener + Usual Care | -5.0 | 20% | Not significant (p=0.53) |
| Usual Care Alone | -5.7 | 22% | Reference group |
This clear result from the blinded assessment indicated that water softeners provided no additional clinical benefit beyond usual eczema care alone 3 .
The objective secondary measures supported the primary findings:
However, an interesting discrepancy emerged from participant-reported outcomes. Parents in the water softener group reported small but statistically significant improvements in some measures, including the Patient-Oriented Eczema Measure (POEM), well-controlled weeks, and the Dermatitis Family Impact questionnaire 1 .
| Assessment Type | Blinded Outcomes (Research Nurses) | Participant-Reported Outcomes |
|---|---|---|
| Eczema Severity | No significant difference | Small but significant improvements |
| Medication Use | No significant difference | Not assessed |
| Night-time Scratching | No significant difference | Not assessed |
| Quality of Life | Not assessed | Significant improvement in family impact |
The economic analysis concluded that ion-exchange water softeners were unlikely to be cost-effective from a healthcare system perspective, given their substantial cost without demonstrated clinical benefit 1 .
Intervention being tested. Supplied by industry consortium; installed to soften all household water except one drinking tap.
Primary outcome measure. Objective severity scale completed by blinded research nurses assessing six body areas.
Objective measure of sleep disturbance. Worn like a wristwatch to capture night-time movement as surrogate for itching.
Patient-reported outcome. Validated tool capturing symptoms important to patients.
| Component | Function in the Study | Specifics/Details |
|---|---|---|
| Ion-Exchange Water Softener | Intervention being tested | Supplied by industry consortium; installed to soften all household water except one drinking tap |
| SASSAD Score | Primary outcome measure | Objective severity scale completed by blinded research nurses assessing six body areas |
| Actiwatch™ Accelerometer | Objective measure of sleep disturbance | Worn like a wristwatch to capture night-time movement as surrogate for itching |
| Patient-Oriented Eczema Measure (POEM) | Patient-reported outcome | Validated tool capturing symptoms important to patients |
| Water Hardness Testing | Eligibility and compliance measure | Ensured participants lived in hard water areas (>200 mg/L calcium carbonate) |
While SWET answered the treatment question definitively, it left open the possibility that water softeners might still play a role in preventing eczema from developing in the first place. The factors that drive eczema development may differ from those that influence flare-ups in established disease.
This reasoning led to the SOFTER trial (Softened Water for Eczema Prevention), a pilot study published in 2022 that investigated whether installing water softeners before birth could reduce eczema risk in high-risk infants 2 .
This trial recruited 80 pregnant women living in hard water areas who had a family history of atopy.
The SOFTER pilot found promising preliminary results—at 6 months of age, 33% of infants in the water softener group had developed visible eczema compared to 48% in the control group 2 .
While these findings are preliminary and based on a small sample, they suggest that water softeners might potentially help prevent eczema development in high-risk infants, even if they don't help treat existing eczema 6 .
The SWET trial delivered a clear message to families struggling with childhood eczema: while the idea that water softeners might help seems logical, robust scientific evidence does not support their use for treating established moderate to severe eczema.
The study demonstrated that eczema severity improved similarly in both groups, indicating that the investment in a water softener is unlikely to provide additional clinical benefit.
The discrepancy between objective measurements and parent reports offers an important lesson about the power of belief in perceived treatment effects. As the researchers noted, parental reports of improvement were "likely the result of response bias," since families knew whether they had received a water softener 1 .
For families considering water softeners specifically for eczema treatment, the evidence suggests redirecting resources toward proven eczema management strategies: consistent emollient use, appropriate topical medications when needed, and identification of personal triggers.
However, for those at the prevention stage—particularly families with a strong history of eczema expecting a new baby—the question remains open, with the SOFTER trial paving the way for future definitive research.
The SWET story exemplifies how rigorous scientific investigation can transform popular belief into evidence-based practice, ensuring families make decisions grounded in science rather than anecdote alone. As one research team eloquently stated, "Water softeners provided no additional benefit to usual care in this study population" 4 —a conclusion that continues to guide dermatological practice today.