The stratum corneum, the outermost layer of the skin, acts as a barrier between the skin and the outside world, preventing evaporation of water from underlying tissues while impeding the diffusion of foreign molecules into the body (1 ,2 ). Densely packed layers of flattened, dead, keratinized cells (2 ,3 ) are incorporated into a lipid lamellae matrix consisting primarily of ceramides, cholesterol, and fatty acids (2 ,4 ), forming an impermeable, hydrophobic partition. The stratum corneum represents the main obstacle to efficient transdermal drug delivery (1 ,2 ). If the stratum corneum is disrupted, the barrier to molecular transport is greatly reduced.
