Solubility of Foreign Molecules in Stratum Corneum Brick and Mortar Structure

The study developed a novel methodology to measure the solubility of chemicals in the stratum corneum (SC), using techniques like NMR and WAXS, without altering SC properties. It focused on the solubility of caffeine and 2-methyl resorcinol (2-MR) at different humidity levels, finding that 2-MR had a higher saturation concentration than caffeine. The solubility decreased with lower humidity. The study also examined minoxidil, used for hair growth, which showed low solubility in SC. The research highlighted that solubility in SC could not be solely explained by traditional factors and that hydration levels significantly impacted SC permeability and chemical safety assessments. This methodology provided insights into the solubility behavior of various compounds and could be applied to other systems with low water content.