ABSTRACT
Introduction ...................................................................................................................................... 67 Stratum Corneum Hydration by Occlusion ..................................................................................... 68 Stratum Corneum Hydration by Exogenous Chemicals ................................................................. 69 Conclusions ...................................................................................................................................... 70 References......................................................................................................................................... 71
Normal skin is a partially hydrated tissue that maintains a consistent water content of approximately 5 to 15%, regardless of how much the humidity of the environment varies. The superficial epidermal layer, the stratum corneum (SC), plays a dual barrier role by minimizing the transepidermal water loss (TEWL), and by preventing external ingress due to its extremely high impermeability. The hydration state of the skin affects the permeability of the SC, thus percutaneous absorption enhancement may be achieved by simply increasing the water content in the SC. While water, an endogenous constituent of skin, acts as the penetration enhancer, it causes minimal irritancy or toxicity to the skin, and any transient manifestations are reversible in a short time. Skin hydration can be achieved quite simply by applying an occlusive vehicle (e.g., an ointment) to the skin [1, 2], or more elegantly by incorporating specific moisturizing factors into the vehicle or by using polymer patch delivery systems.
