The influence of specific follicle properties, sebum production and hair growth on the follicular penetration of topically applied substances was investigated. The behavior of follicles identified in selected skin areas of volunteers was analyzed by various tape stripping and staining methods in combination with laser scanning microscopy. Furthermore hair growth in the selected skin areas was determined. A correlation between sebum production, hair growth activity and follicular penetration was observed.

The accurate determination of the mass of the horny layer removed by tape stripping is a decisive prerequisite for the application of this technique in penetration studies. A novel method using optical spectroscopy to determine the amount of stratum corneum (SC) is presented. We could show that the absorbance measured in the visible spectral range accurately reflects the mass of the SC fixed on individual tapes. Furthermore, absorbance measurement allows determination of the absolute mass of corneocyte aggregates on the removed tape strips. Topically applied substances do not disturb the spectroscopic measurements in contrast to the conventionally employed weight determination. Identical results were obtained when performing spectroscopic horny layer quantification independently in two separate institutions. Taken together, this new method is rapid, sensitive, reproducible, and accurate. We anticipate a wide application in penetration studies as well as in dermatopharmacokinetics.

Tape-stripping and optical spectroscopy are used as a suitable combined method to determine the horny layer profile. Firstly, typical ultraviolet filter substances are used as active substances which are fixed inside the horny layer. Secondly, clobetasol propionate was applied topically in two formulations, Temovate^® Cream and Temovate Ε Emollient^®. The measured changes in the local distribution of the drug inside stratum corneum reflect the observed differences in the biological response visualized as blanching. The concentration of the drug in deeper parts of the horny layer proposes the existence of a small channel available for the percutaneous absorption. The observed low intensity blanching is correlated to the follicle orifices of the skin. After application of Temovate Ε Emollient^®, a lateral spreading of the drug must be taken into account.

Tape stripping is a well-known method to study the barrier function of the stratum corneum (SC) and penetration processes of topically applied substances into the horny layer. The quantification of the removed corneocytes for each tape strip is the prerequisite for these studies. The pseudo-absorption of the corneocytes was proposed as a measure for the quantification of the removed corneocyte aggregates. In this study, the pseudo-absorption of the corneocytes in the visible range (430 nm) is compared with the protein absorption in the UV range (278 nm) and an absorption at 652 nm obtained after staining of the SC proteins with Trypan blue. Both the protein absorption and the absorption measured after staining correlate well with the pseudo-absorption measured at 430 nm (R² = 0.92 ± 0.04 and R² = 0.95 ± 0.04, respectively).