Editing Cholesterol (section)

====Epidermis====
The stratum corneum is the outermost layer of the epidermis.<ref name="Elias-2006">{{cite book | vauthors = Elias PM, Feingold KR | chapter = Stratum Corneum Barrier Function: Definitions and Broad Concepts | veditors = Elias PM |title=Skin barrier |date=2006 |publisher=Taylor & Francis |location=New York |isbn=978-0824758158}}</ref><ref name="Merleev et al-2022" /> It is composed of terminally differentiated and enucleated [[corneocyte]]s that reside within a lipid matrix, like "bricks and mortar."<ref name="Elias-2006" /><ref name="Merleev et al-2022">{{cite journal | vauthors = Merleev AA, Le ST, Alexanian C, Toussi A, Xie Y, Marusina AI, Watkins SM, Patel F, Billi AC, Wiedemann J, Izumiya Y, Kumar A, Uppala R, Kahlenberg JM, Liu FT, Adamopoulos IE, Wang EA, Ma C, Cheng MY, Xiong H, Kirane A, Luxardi G, Andersen B, Tsoi LC, Lebrilla CB, Gudjonsson JE, Maverakis E | title = Biogeographic and disease-specific alterations in epidermal lipid composition and single-cell analysis of acral keratinocytes | journal = JCI Insight | volume = 7 | issue = 16 | date = August 2022 | pmid = 35900871 | pmc = 9462509 | doi = 10.1172/jci.insight.159762 }}</ref> Together with [[ceramide]]s and free fatty acids, cholesterol forms the lipid mortar, a water-impermeable barrier that prevents evaporative water loss. As a rule of thumb, the epidermal lipid matrix is composed of an equimolar mixture of ceramides (≈50% by weight), cholesterol (≈25% by weight), and free fatty acids (≈15% by weight), with smaller quantities of other lipids also being present.<ref name="Elias-2006" /><ref name="Merleev et al-2022" /> Cholesterol sulfate reaches its highest concentration in the granular layer of the epidermis. Steroid sulfate sulfatase then decreases its concentration in the stratum corneum, the outermost layer of the epidermis.<ref>{{cite journal | vauthors = Elias PM, Williams ML, Maloney ME, Bonifas JA, Brown BE, Grayson S, Epstein EH | title = Stratum corneum lipids in disorders of cornification. Steroid sulfatase and cholesterol sulfate in normal desquamation and the pathogenesis of recessive X-linked ichthyosis | journal = The Journal of Clinical Investigation | volume = 74 | issue = 4 | pages = 1414–1421 | date = October 1984 | pmid = 6592175 | pmc = 425309 | doi = 10.1172/JCI111552 }}</ref> The relative abundance of cholesterol sulfate in the epidermis varies across different body sites with the heel of the foot having the lowest concentration.<ref name="Merleev et al-2022" />