Which Skin Model Is the Most Appropriate for the Investigation of Topically Applied Substances into the Hair Follicles?

Abstract

It has recently been demonstrated by the utilization of different techniques, such as differential stripping and laser scanning microscopy, that the hair follicles represent an efficient long-term reservoir for topically applied substances. In the present paper, the different in vivo techniques are compared to those of in vitro analysis. It was found that in vitro measurements on pig ear skin are highly superior for the analysis of follicular penetration, as compared to in vitro investigations on excised human skin, mainly due to the fact that the human skin contracts after removal. Restretching of the skin to its original size mainly stretches the interfollicular fibres, whereas the fibres around the hair follicles remain contracted. In contrast to excised human skin, pig ear tissue does not contract when the cartilage is not removed. Moreover, it has an intact barrier on both sides of the ear. Regardless of the fact that the hair follicles on pig ear skin are larger than those of humans, the porcine ear skin represents a more suitable in vitro model for the analysis of the penetration and storage of topically applied substances in the hair follicles than excised human skin.

Setup for investigating gold nanoparticle penetration through reconstructed skin and comparison to published human skin data

“…Furthermore, it was shown that excised human skin gives different results regarding hair follicle penetration compared to in vivo investigations, due to shrinkage of the hair follicles in vitro on cutting. 40 Fig . 5 Representative overlaid multiphoton/transmission image showing exclusive localization of gold nanoparticles (indicated as white spots) in the Stratum Corneum after 2 h of skin exposure and no penetration into the deeper skin layers.…”

In vitro skin models as a tool in optimization of drug formulation

“…Namely, re-stretching of the skin to its original size mainly stretches the interfollicular fibers, whereas the fibers around the hair follicles remain 23 contracted. In contrast to excised human skin, pig ear tissue does not contract when the cartilage is not removed (Lademann et al, 2010). The pig skin is readily obtained as a waste from animals slaughtered for food.…”

Nanotechnology-Based Cosmetics for Hair Care

“…One such technique utilized by many of the aforementioned experiments is cyanoacrylate skin surface stripping, which has been found to improve follicular penetration of a variety of transcutaneously applied compounds by removing the horny layer as well as contents of the upper follicular orifice [15]. While this model is a valuable tool to assess penetration into the hair follicle, it effectively opens hair follicles and increases the reservoir function of the hair follicle, which may not translate into intact human skin [23]. Furthermore, in vitro investigations on excised human skin demonstrated a significantly higher amount of drug penetration and storage as compared to in vivo conditions [24].…”