Background: Hard water is associated with atopic dermatitis (eczema). We wanted to determine if a baby cleanser and its individual components altered free ionized calcium (Ca2+) in?a simulated hard water baby bath. For these studies, an in vitro determination of free Ca2+ in a?simulated hard water baby bath, and an in vivo exploratory study of free Ca2+ absorption into skin from hard water were performed. Methods: Free Ca2+ was measured with an ion-sensitive electrode in vitro in hard water (100–500?ppm, Ca2+) before and after addition of the cleanser and/or its components. In an exploratory study, absorption of Ca2+ into skin from hard water was determined in three female participants (aged 21–29 years). Results: At an in-use dilution of 1%, the test cleanser reduced free Ca2+ from ~500 ppm to 2+. The anionic surfactant component contributed the most to this effect. In the exploratory in vivo study, we measured a reduction of ~15% in free Ca2+ from simulated hard water over 10 minutes. Conclusion: Baby cleansers can bind free Ca2+ and reduce the effective water hardness of bath water. Reducing the amount of free Ca2+ in the water will reduce the availability of the ion for binding to the skin. Altering or reducing free Ca2+ concentrations in bath water may be an important parameter in creating the ideal baby bath.
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