||Ovaere P, Lippens S, Vandenabeele P, Declercq W. The emerging roles of serine protease cascades in the epidermis. Trends Biochem Sci. 2009 Sep34(9):453-63. doi: 10.1016/j.tibs.2009.08.001. p.453 left column bottom paragraphPubMed ID19726197
||E. Candi, et al. The cornified envelope: a model of cell death in the skin Nat. Rev. Mol. Cell Biol., 6 (2005), pp. 328–340PubMed ID15803139
||p.453 left column bottom paragraph:"We are persistently exposed to environmental hazards. The first protective barrier is provided by the skin, our largest organ. It serves as the interface between the organism and the outside world and it serves many functions, such as the retention of body fluids, maintenance of body temperature, and protection against UV-light, chemical influxes, wounds, and the invasion of micro-organisms. The protective barrier function is performed by the keratinocytes of the epidermis, which are continuously produced by proliferating stem cells of the basal layer or stratum basale and differentiate during a 14 day journey towards the surface [primary source]."