SWET Trial

Design and population. The Softened Water Eczema Trial (Thomas et al., PLoS Med 2011) was an observer-blind, pragmatic RCT run from Nottingham with NIHR HTA funding. It randomised 336 children aged 6 months to 16 years with moderate or severe Atopic Dermatitis, all living in Hard Water areas of England (≥200 mg/L calcium carbonate). It was prompted by observational links between hard water and childhood eczema and by many anecdotal reports of skin improving after moving to soft-water areas. SWET Trial [relates] Hard Water

Intervention and primary outcome. The intervention group had an ion-exchange water softener installed in the home (about 12 days after randomisation) and used it for 12 weeks; all incoming water was softened except a drinking tap in the kitchen. Both groups continued usual eczema care. The primary outcome was change in SASSAD (Six Area Six Sign Atopic Dermatitis) severity score at 12 weeks, measured by research nurses blinded to allocation. Night-time movement was measured with wrist accelerometers as an objective marker of scratching and sleep loss. SWET Trial [relates] Atopic Dermatitis

Result. Both groups improved by a similar amount: SASSAD fell by 5.0 (20%) with a softener and 5.7 (22%) with usual care (mean difference 0.66, 95% CI −1.37 to 2.69; p = 0.53). Night-time movement and use of Topical Corticosteroids or Topical Calcineurin Inhibitors did not differ. Parents in the softener group reported small improvements in some secondary outcomes, which the authors attributed to response bias because families knew their allocation. Just over half of softener families chose to buy the unit afterwards. SWET Trial [contradicts] Hard Water

Limitations. A sham softener was not feasible because softened water feels different and makes more suds, so blinding relied on nurse assessors. The 12-week duration was short, although there was no sign of a late divergence between groups. Objective outcomes may miss benefits parents value, such as perceived dryness. SWET tested treatment of established eczema, not whether soft water from birth prevents it; prevention trials remain at pilot stage (Jabbar-Lopez 2021). SWET Trial [relates] Bathing Frequency

What it means for toddlers. Parents in hard-water areas do not need to buy a water softener to treat a toddler’s eczema. Effort is better spent on what goes into the bath: Soap Substitutes instead of soap or bubble bath, good rinsing, and leave-on emollient straight afterwards. Whether hard water helps cause eczema in babies with Filaggrin mutations is a separate, unresolved question (see Hard Water). SWET Trial [supports] Soap Substitutes

Connections

• Hard Water — RCT found softeners no help for established eczema, source: Thomas, PLoS Med 2011
• Bathing Frequency — part of evidence that changing bath water adds little, source: SWET 2011
• Soap Substitutes — practical alternative to softening water, source: SWET discussion
• Filaggrin — gene–environment question SWET did not test, source: Hard Water note
• Topical Corticosteroids — usage did not differ between arms, source: Thomas 2011