Keratinocytes account for most of the cells in the epidermis of the human skin. The epidermis is situated directly above the dermis, separated by the basement membrane. Dermal keratinocytes build up the stratifying epithelial tissue although other cell types like melanocytes are additionally found in this area. Here, they build four macroscopically discriminable layers from which they differentiate. Proliferation proceeds upwards from the basal layer (stratum basale) via stratum spinosum and stratum granulosum to the stratum corneum where these keratinocytes assemble a constant barrier of the skin. In this proliferating process, the dermal keratinocytes terminally differentiate whereby their nuclei and organelles collapse [65]. To ensure the constant proliferation and the integrity of our skin, multipotent stem cells can rebuild the dermal keratinocytes [66]. Beside dermal occurrence, keratinocytes are also present in hair follicles. Hair follicles are embedded in the dermis and are not visible on the surface of the skin. Figure 2 shows the structure of a normal human hair. The invisible part of the human hair is enclosed by two root sheaths, the inner (IRS) and outer (ORS) root
