The effect of vehicle on skin absorption of Mg 2+ and Ca 2+ 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 Mg ²⁺ and Ca ²⁺ from those formulations was studied in vitro using static Franz diffusion cells under infinite dose condition and under occlusion of the apparatus.
Results: Mg ²⁺ and Ca ²⁺ penetrate skin samples from TSW. Encapsulating TSW into double emulsion (TSW/O/W) increased skin absorption of both cations of interest and kept the Ca ²⁺ /Mg ²⁺ ratio equal to that of TSW in each skin layer. The dermal absorption of Mg ²⁺ from the double emulsion departs from both single emulsions. Application of liposome suspension improved the skin absorption of Ca ²⁺ while keeping constant that of Mg ²⁺ , leading to unbalanced Ca ²⁺ /Mg ²⁺ ratio inside skin.
Conclusion: The beneficial effects of TSW are not only due to their action on the skin surface. Their active components, especially Ca ²⁺ and Mg ²⁺ cations, reach viable skin layers in a formulation-dependent manner. The distribution of ions inside skin depends on the type of formulation.
(© 2020 Society of Cosmetic Scientists and the Société Française de Cosmétologie.)