Pedro Contreiras

Water on the Skin: Intrinsic Water Retention Capacity a new Parameter based on Mathematical Modeling of TEWL and Skin hydration methods



Skin functionality relies on a highly regulated cutaneous water balance that supports barrier integrity and biomechanical properties. Stratum corneum (SC) hydration is mainly ruled by the water gradient between the surface and deeper layers, and is transiently affected by environmental conditions (temperature, humidity) and influenced by topical products such as humectants and emollients. Because instantaneous measurements provide limited insight into these dynamics, an intrinsic descriptor of the skin’s ability to maintain optimal hydration is needed.

PhD Trials developed a new parameter, Intrinsic Water Retention Capacity (IWRC), to detect the system ability to conserve and replenish water across the SC and viable epidermis. This parameter, obtained by disposition–decomposition analysis (DDA) is calculated by simultaneously modelling transepidermal water loss (TEWL) and epidermal “capacitance.” TEWL captures net water evaporation at the surface, while capacitance primarily reflects the behavior of water molecules transiently retained in superficial epidermal structures. Using the plastic occlusion stress test (POST) to induce controlled over-hydration, TEWL and capacitance time profiles are analyzed to separate superficial disposition effects from deeper-layer hydration equilibrium resulting in the new Intrinsic Water Retention Capacity parameter. We also show how different products can affect the parameter contributing to increase the Skin Water Holding Capacity.