Quantification of the horny layer using tape stripping and microscopic techniques

Abstract

Tape stripping is a method well suited for studying the penetration of topically applied substances into the upper part of the skin, the stratum corneum (SC). The amount of topically applied substances removed by each tape strip can be determined by common analytical methods. These amounts have to be correlated with their location within the horny layer in order to determine penetration profiles. Therefore the amount of SC on each removed strip must be determined. In the study reported, this amount was derived from the covering density of the SC cells, the corneocytes, on tape strips using classic microscopic techniques and laser scanning microscopy. The amount of corneocytes determined by both microscopic methods shows a good correlation (R2 +/- S.D.= 0.95 +/- 0.02) with the pseudoabsorption of the corneocytes, a method usually used to determine the SC amount on the removed strips. These measurements require the application of a special spectrometer, whereas the covering density can easily be determined using widely available microscopic equipment. The penetration of a typical UV filter, butyl methoxydibenzoylmethane, applied at two different formulations, was studied using the microscopic method developed. The calculated penetration profiles show that the applied formulation influences the amount of corneocytes on the removed strips.