Hard water softening effect of a baby cleanser

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 (Ca(2+)) in a simulated hard water baby bath. For these studies, an in vitro determination of free Ca(2+) in a simulated hard water baby bath, and an in vivo exploratory study of free Ca(2+) absorption into skin from hard water were performed. METHODS: Free Ca(2+) was measured with an ion-sensitive electrode in vitro in hard water (100–500 ppm, Ca(2+)) before and after addition of the cleanser and/or its components. In an exploratory study, absorption of Ca(2+) 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 Ca(2+) from ~500 ppm to <200 ppm; a 10% in-use dilution bound virtually all free Ca(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 Ca(2+) from simulated hard water over 10 minutes. CONCLUSION: Baby cleansers can bind free Ca(2+) and reduce the effective water hardness of bath water. Reducing the amount of free Ca(2+) in the water will reduce the availability of the ion for binding to the skin. Altering or reducing free Ca(2+) concentrations in bath water may be an important parameter in creating the ideal baby bath.