Human skin, nature stratum corneum

In terms of the mechanisms of action, the pyrrolidones partition well into human horny layer. They may act by altering the solvent nature of the membrane and pyrrolidones have been used to generate reservoirs within skin membranes. Such a reservoir effect offers potential for sustained release of a permeant from the stratum corneum over extended time periods. However, as with many other potential enhancers, clinical use of pyrrolidones is problematic due to adverse reactions. An in vivo vasoconstrictor bioavailability study demonstrated that pyrrolidones caused erythema in some volunteers, although this effect was relatively short-lived. Also, a toxic hygroscopic contact reaction to NMP has been reported recently [21]. 

A natural concentration gradient across human skin exists the inner dermal layer is essentially fully hydrated whereas the outer stratum corneum water content depends on external factors such as relative humidity and temperature typically, stratum corneum water content is around 20-30% of the tissue dry weight. Of this, approximately 25-35% is associated with some structural component of the tissue (i.e. bound ) with the remainder free (Walkley, 1972). Increasing the water content of the barrier stratum corneum is well known to... 

Testing Using Animal Skin. Human skin is unique in the thickness of its stratum corneum, density of hair follicles, and the nature of its sweat glands [77]. Pieces of skin from animals such as pigs are frequently used in testing the activity of topicals against bacteria [78], but only limited published information is available on the application of this model to viruses [26]. 

---