N. Otberg, H. Richter, U. Jacobi, U. Blume-Peytavi, H. Schaefer, W. Sterry, J. Lademann

Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology and Allergology, Charité - Universitätsmedizin, Berlin, Germany

The knowledge of permeation and penetration processes is the prerequisite for the development and optimisation of drugs and cosmetics. In the past, percutaneous absorption was described as diffusion through the lipid domains of the stratum corneum. It was presumed that skin appendages, which mean hair follicles and sweat glands, play a subordinate role in absorption processes. The amount of appendages of the total skin surface was estimated to be less than 0.1%. But previous studies show higher absorption rates in skin areas with a high follicle density. However, follicle size and density have never been correlated with the amount of the absorbed drug. In the present study, characteristics of follicle sizes and potential follicular reservoir were determined in cyanoacrylate skin surface biopsies, removed from 7 different skin areas (lateral forehead, back, thorax, upper arm, forearm, thigh and sural region). The highest hair follicle density, percentage of follicular orifices on the skin surface and infundibular surface, were found on the forehead, the highest average size of the follicular orifices was measured in the sural region. The highest infundibular volume and therefore a potential follicular reservoir were calculated for the forehead and for the sural region, although the sural region showed the lowest hair follicle density. The calculated follicular reservoir volume of these two skin areas was as high as the estimated reservoir of the stratum corneum. The lowest values for every other parameter were found on the forearm. The statement that the amount of appendages of the total skin surface is less than 0.1% can be refuted by the present study. Every body region has its own hair follicle characteristics, which should lead to a differential evaluation of skin penetration experiments.