Hardness in water is consisted with mineral salts, including calcium (Ca++) and magnesium (Mg++). The mineral salts react with soap to form an insoluble precipitate known as metallic soap (soap scum). Since metallic soap remains tightly on the skin and is hard to rinse off, it may become one of irritants that exacerbate dermatitis. In this study, we used cation-exchange resin to prepare ultra-pure soft water (UPSW) excluding both Ca++ and Mg++, and investigated effect of UPSW rinsing on skin conditions in subjects with atopic dermatitis. Furthermore, antigenic activity of metallic soap was investigated by in vivo experiments.
Methods:
Stratum corneum was collected from arms of healthy volunteers who rinsed soap in tap water or UPSW, and the quantity of remained soap scum was determined with a gas chromatography. After 4 weeks of bathing in UPSW, the water content of the stratum corneum and transepidermal water loss (TEWL) of volunteers with mild atopic dermatitis were measured. With atopic NC/Tnd mice, a model for atopic dermatitis, we attempted to confirm results obtained from atopic volunteers. Plasma total IgE was measured by an ELISA after immunization of mice with metallic soap.
Results:
On skins rinsed in UPSW, soap was disappeared immediately and remained metallic soap was significantly reduced when compared to that on skins rinsed in tap water. In skins of atopic volunteers who used UPSW for bath, the water content in stratum corneum was increased and TEWL was decreased. Skin dryness and itch scores were reduced in most volunteers. After washed with soap and rinsed in UPSW for 2 weeks, severe dermatitis of NC/Tnd mice were reduced as well as TEWL. On the other hand, dermatitis in NC/Tnd mice rinsed in tap water became worse. Plasma total IgE was increased in mice that were immunized with metallic soap.
Conclusions: UPSW protected skins from residue of metallic soap. Metallic soap has antigenic activity and increased plasma IgE levels. Clinical symptoms and the skin barrier function were improved by the use of soap with UPSW. UPSW is beneficial for the skin of patients with atopic dermatitis.