difference centers around the increased prominence and number of hair follicles. Probably diffusion across the transfollicular shunt is greatly enhanced, to the point where it becomes the principal pathway. The horny layer of the epidermis is also affected by the formation of a thick coat of hair. Since the hairy mat restricts insensible perspiration, the stratum corneum associated with furry skin need not be as impermeable to water, and it is typically thinner and less well formed than when the surface is hairless. Thus, structural and compositional changes in the horny layer also provide a basis for explaining the differing hydration sensitivities. It is likely that both factors are important.
This study provides further evidence of intra-and interspecies complexities of animal skins as mass transport regulators. To a degree it demonstrates that skins covered with thick coats of hair do not behave diffusionally as hairless skins, whether of mouse or humans. Previous work (1-8) indicates a high degree of parallelism in the chemical barrier properties of hairless mouse and human skins. This study adds support for the use of hairless animals for research on percutaneous absorption, primary irritancy, topical drug delivery, etc., when it is not possible or practicable to use human subjects.