The skin exhibits several essential functions, the major one being the containment function. It provides protection from various external insults that include: microorganisms, chemicals, electricity, mechanical pressure and heat. The skin also filters about 70% of UVB radiation and plays a key role in the regulation of body temperature. It contains several subtissues that differ in structure and function.
The stratum corneum (SC) is part o fthe epidermis and is the outermost upper layer of the skin. It provides the rate-limiting barrier for penetration into and through the skin. The dermis lies beneath the epidermis and under it, the subcutaneous tissue. The skin also includes sebaceous glands and hair follicles.
In order to allow a desired interaction between a compound and the skin, a manipulation of this heterogeneous barrier structure is required. When applied to the skin, a compound may partition into the SC, diffuse and possibly penetrate. Its partition and diffusion profiles can vary depending on its interaction with the sub-tissue. The compound’s pathway of removal or clearance from the skin will be highly dependent upon its level of penetration. The amount of the compound remaining on the surface of the skin will eventually be removed with the dead corneocytes during the desquamation process. The amount penetrated to the living epidermis and absorbed through blood vessels will be cleared through the circulation and is prone to metabolism.