M. Ossadnik*, S. Koch*, N. Otberg**, H. Richter**, U. Jacobi**, W. Sterry**, J. Lademann**

*Humaine Klinikum, Ost-Brandenburgisches Tumorzentrum, D-15526 Bad Saarow, Germany, **Center of Experimental and Applied Cutaneous Physiology, Department of Dermatology and Allergology, Charité - Universitätsmedizin, Berlin, Germany

A method was developed to determine selectively the amount of topically applied substances penetrating into the orifices of hair follicles. After topical application of formulations, the upper part of the stratum corneum, containing the highest concentration of topically applied substances, was removed by tape stripping. After this procedure, the formulation was only located in the follicle orifices. These follicle contents were removed by cyanoacrylate surface biopsy.

As a first step, this method was tested on porcine ear skin to demonstrate that the amount of topically applied substances stored in the reservoir of the stratum corneum could be completely removed by tape stripping. These investigations were carried out with a formulation containing the dye Patent blue V. After removal of 20 tapes strips the dye was completely removed. It remained in the follicle orifices only.

As a next step, cyanoacrylate surface biopsies were removed from skin, which was stripped. Punch biopsies were taken from this skin area after removal of the cyanoacrylate surface biopsies. The histological sections demonstrate that the follicle content was removed completely by this procedure.

Based on these results, a standard protocol for this differential tape stripping (combination of tape stripping with cyanoacrylate surface biopsy) has been developed. This protocol was used in in vivo experiments on human skin to investigate how efficiently a topically applied antimycotic agent penetrates into the follicle orifices.

Therefore, the cyanoacrylate surface biopsies removed after tape stripping from the treated and untreated skin was brought in contact with a mycotic culture. In the case of the follicle content being removed from the skin treated with the antimycotic agent, the growth of the fungus cells was inhibited. The method of differential tape stripping could be used for the investigation of penetration and action of topically applied substances in the hair follicles.