Editing Skin condition (section)

=== Epidermis ===
{{Main|Epidermis (skin)}}

The epidermis is the most superficial layer of skin, a [[epithelium|squamous epithelium]] with several [[stratum|strata]]: the [[stratum corneum]], [[stratum lucidum]], [[stratum granulosum]], [[stratum spinosum]], and [[stratum germinativum|stratum basale]].<ref name="Fitz" /> Nourishment is provided to these layers via [[diffusion]] from the dermis, since the epidermis is without direct blood supply.<ref>{{cite web | vauthors = Amirlak B, Shahabi L | veditors = Talavera F, Stadelmann WK, Caputy GG |title=Skin Anatomy|url=http://emedicine.medscape.com/article/1294744-overview|publisher=Medscape|access-date=3 June 2013}}</ref> The epidermis contains four cell types: [[keratinocyte]]s, [[melanocyte]]s, [[Langerhans cell]]s, and [[Merkel cell]]s. Of these, keratinocytes are the major component, constituting roughly 95% of the epidermis.<ref name="RooksCD" /> This stratified squamous epithelium is maintained by cell division within the stratum basale, in which differentiating cells slowly displace outwards through the stratum spinosum to the stratum corneum, where cells are continually shed from the surface.<ref name="RooksCD" /> In normal skin, the rate of production equals the rate of loss; about two weeks are needed for a cell to migrate from the basal cell layer to the top of the granular cell layer, and an additional two weeks to cross the stratum corneum.<ref name="bolognia">{{cite book | vauthors = Bolognia JL, Jorizzo JL, Rapini RP |title=Dermatology |publisher=Mosby |location=St. Louis |year=2007 |isbn=978-1-4160-2999-1 }}</ref>