The effect of vehicle on skin absorption of Mg2+ and Ca2+ from thermal spring water

Objective Thermal spring waters (TSW) are commonly used as active ingredients in cosmetics. Their biological activities directly depend on the ionic composition of the spring. However, in order to exhibit beneficial properties, the minerals need to reach viable skin layers. The present study addresses the incorporation of marketed TSW in model cosmetic formulations and the impact of the formulation on skin absorption of magnesium and calcium ions that are known to improve skin barrier function. Methods Marketed TSW was introduced into five formulations. Liposomes were prepared using saturated or unsaturated phospholipids mixed with cholesterol by the thin layer evaporation technique. Emulsions water-in-oil (W/O), oil-in-water (O/W) or double: water-in-oil-in-water (W/O/W) were prepared by high-shear mixing. Skin absorption of Mg2+ and Ca2+ from those formulations was studied in vitro using static Franz diffusion cells under infinite dose condition and under occlusion of the apparatus. Results Mg2+ and Ca2+ penetrate skin samples from TSW. Encapsulating TSW into double emulsion (TSW/O/W) increased skin absorption of both cations of interest and kept the Ca2+/Mg2+ ratio equal to that of TSW in each skin layer. The dermal absorption of Mg2+ from the double emulsion departs from both single emulsions. Application of liposome suspension improved the skin absorption of Ca2+ while keeping constant that of Mg2+, leading to unbalanced Ca2+/Mg2+ ratio inside skin. Conclusion The beneficial effects of TSW are not only due to their action on the skin surface. Their active components, especially Ca2+ and Mg2+ cations, reach viable skin layers in a formulation-dependent manner. The distribution of ions inside skin depends on the type of formulation.