BACKGROUND Hard domestic water has been reported to worsen atopic eczema (AE) and may contribute to its development in early life. OBJECTIVE To review the literature on the relationship between the effect of water hardness (high calcium carbonate; CaCO3 ) on a) the risk of developing AE, b) the treatment of existing AE, and c) skin barrier function in human and animal studies. DESIGN, DATA SOURCES AND ELIGIBILITY CRITERIA We systematically searched databases (MEDLINE, Embase, Cochrane CENTRAL, GREAT and Web of Science) from inception until 30/6/2020. Human and animal observational and experimental studies were included. The primary outcomes were risk of AE and skin barrier function. Studies were meta-analysed using a random-effects model. Evidence certainty was evaluated using the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) approach. RESULTS Sixteen studies were included. Pooled observational data from 7 studies on 385,901 participants identified increased odds of AE in children exposed to harder versus softer water (odds ratio 1.28, 95% CI 1.09, 1.50; GRADE certainty: very low). Two mechanistic studies in humans reported higher deposition of the detergent sodium lauryl sulphate in those exposed to harder versus softer water. Two randomized controlled trials comparing water softeners with standard care did not show a significant difference in objective AE severity with softened water (standardised mean difference 0.06 standard deviations higher, 95% CI 0.16 lower to 0.27 higher; GRADE certainty: moderate). CONCLUSIONS & CLINICAL RELEVANCE There was a positive association between living in a hard-water (range: 76 to >350 mg/L CaCO3 ) area and AE in children. There is no evidence that domestic water softeners improve objective disease severity in established AE. There may be a role of water hardness in the initiation of skin inflammation in early life, but there is a need for further longitudinal and interventional studies.

中文翻译：

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水硬度对特应性湿疹和皮肤屏障功能的影响：系统评价和荟萃分析

背景据报道，硬生活用水会使特应性湿疹 (AE) 恶化，并且可能有助于其在生命早期的发展。目的 回顾有关水硬度（高碳酸钙；CaCO3）对 a) 发生 AE 的风险、b) 现有 AE 的治疗和 c) 人类和动物研究中皮肤屏障功能的影响之间关系的文献。设计、数据来源和资格标准 我们系统地检索了数据库（MEDLINE、Embase、Cochrane CENTRAL、GREAT 和 Web of Science），从开始到 2020 年 6 月 30 日。包括人类和动物观察和实验研究。主要结果是 AE 风险和皮肤屏障功能。使用随机效应模型对研究进行荟萃分析。使用推荐分级、评估、开发和评估 (GRADE) 方法。结果 纳入了 16 项研究。来自 385,901 名参与者的 7 项研究的汇总观察数据确定，暴露于较硬水与较软水的儿童发生 AE 的几率增加（几率比 1.28，95% CI 1.09，1.50；等级确定性：非常低）。两项针对人体的机械研究报告称，与较软的水相比，接触较硬水的人中十二烷基硫酸钠的洗涤剂沉积量更高。两项比较软水器与标准护理的随机对照试验并未显示软化水的客观 AE 严重程度存在显着差异（标准化平均差高 0.06 标准偏差，95% CI 0.16 低至 0.27；等级确定性：中等）。结论和临床相关性 生活在硬水中（范围：76 到 > 350 mg/L CaCO3 ) 面积和儿童 AE。没有证据表明家用软水器可以改善已确定 AE 的客观疾病严重程度。水硬度可能在生命早期引发皮肤炎症中起作用，但需要进一步的纵向和干预研究。