Hard water softening effect of a baby cleanser

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.

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).

At an in-use dilution of 1%, the test cleanser reduced free Ca²⁺ from ~500 ppm to <200 ppm; a 10% in-use dilution bound virtually all free Ca²⁺. 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.

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.