The Effects of Hard Water on Human Hair: A Systematic Review and Meta-analysis
Chingshubam Bikash, Rashmi Sarkar, Shanthosh Priyan SundaramABSTRACT
Background:
The accumulation of hard water metals in human hair has been observed. Its effects on hair health become pertinent as it is often implicated in poor hair quality. We aimed to review the relevant literature systematically and analyze the effects of hard water on (i) the deposition of hard water metals and (ii) the objective and subjective hair health.
Methods:
Pre-registration with PROSPERO was done. We searched PubMed, Cochrane CENTRAL, DOAJ, and EBSCOhost from inception till December 31, 2024. Human observational and experimental studies were included and meta-analyzed using a random effects model. Risk of bias was assessed using the Risk of Bias in Non-randomized Studies of Interventions I tool and the National Institute of Health quality assessment tool. The evidence was ascertained using the GRADE tool.
Results:
Nine studies were included. The calcium and magnesium deposition were higher by 2.07 standard deviation (SD) and 1.88 SD with hard water than with soft water. The tensile strength decreased by 0.282 SD when treated with hard water. The break stress, elastic modulus, shear modulus, combing forces, style retention, and surface irregularities increased with hard water treatment. There seems to be a positive correlation between ion deposition and the hardness of water, pH, and hair treatments. The subjective hair health is negatively impacted by hard water.
Conclusion:
The certainty of evidence was moderate for the decrease in tensile strength, whereas it was very low for the rest of the estimates. Hard water probably increases hair breakage due to significant deposition of calcium and magnesium ions, but more robust, real-world studies can provide a greater validation.