Comparison of two in vitro models for the analysis of follicular penetration and its prevention by barrier emulsions.

The penetration of topically applied substances in and through the human skin is of special interest for the development and optimization of topically applied drugs and cosmetic products. In the present study, the efficacy of barrier emulsions in the prevention of the penetration of pollen allergens into the hair follicles was investigated. Because of the sensitising potential of the used pollen allergens, the study was carried out under in vitro conditions. Therefore, excised human skin and porcine ear skin were used as tissue models. Applying laser-scanning microscopy and fluorescent-labeled grass pollen allergens, we found that the preventive efficacy of the barrier emulsions could be significantly better investigated on porcine ear skin than on excised human skin. This might be due to the contraction of the elastic fibres around the hair follicles in excised human skin after its removal. In contrast to the excised human skin, the porcine ear skin remains on the cartilage during the experiment. Therefore, contraction of the tissue can be avoided. The results give further indication that in vitro studies based on membranes of excised skin are not suitable for the investigation of the follicular penetration pathway of topically applied substances.