List of skin conditions

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Young child with a red rash covering face, chest, shoulders, and arms
Rash due to measles

Many skin conditions affect the human integumentary system—the organ system covering the entire surface of the body and composed of skin, hair, nails, and related muscle and glands.[1] The major function of this system is as a barrier against the external environment.[2] The skin weighs an average of four kilograms, covers an area of two square metres, and is made of three distinct layers: the epidermis, dermis, and subcutaneous tissue.[1] The two main types of human skin are: glabrous skin, the hairless skin on the palms and soles (also referred to as the "palmoplantar" surfaces), and hair-bearing skin.[3] Within the latter type, the hairs occur in structures called pilosebaceous units, each with hair follicle, sebaceous gland, and associated arrector pili muscle.[4] In the embryo, the epidermis, hair, and glands form from the ectoderm, which is chemically influenced by the underlying mesoderm that forms the dermis and subcutaneous tissues.[5][6][7]

The epidermis is the most superficial layer of skin, a squamous epithelium with several strata: the stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale.[8] Nourishment is provided to these layers by diffusion from the dermis since the epidermis is without direct blood supply. The epidermis contains four cell types: keratinocytes, melanocytes, Langerhans cells, and Merkel cells. Of these, keratinocytes are the major component, constituting roughly 95 percent of the epidermis.[3] 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.[3] 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.[9]

The dermis is the layer of skin between the epidermis and subcutaneous tissue, and comprises two sections, the papillary dermis and the reticular dermis.[10] The superficial papillary dermis interdigitates with the overlying rete ridges of the epidermis, between which the two layers interact through the basement membrane zone.[10] Structural components of the dermis are collagen, elastic fibers, and ground substance.[10] Within these components are the pilosebaceous units, arrector pili muscles, and the eccrine and apocrine glands.[8] The dermis contains two vascular networks that run parallel to the skin surface—one superficial and one deep plexus—which are connected by vertical communicating vessels.[8][11] The function of blood vessels within the dermis is fourfold: to supply nutrition, to regulate temperature, to modulate inflammation, and to participate in wound healing.[12][13]

The subcutaneous tissue is a layer of fat between the dermis and underlying fascia.[14] This tissue may be further divided into two components, the actual fatty layer, or panniculus adiposus, and a deeper vestigial layer of muscle, the panniculus carnosus.[3] The main cellular component of this tissue is the adipocyte, or fat cell.[14] The structure of this tissue is composed of septal (i.e. linear strands) and lobular compartments, which differ in microscopic appearance.[8] Functionally, the subcutaneous fat insulates the body, absorbs trauma, and serves as a reserve energy source.[14]

Conditions of the human integumentary system constitute a broad spectrum of diseases, also known as dermatoses, as well as many nonpathologic states (like, in certain circumstances, melanonychia and racquet nails).[15][16] While only a small number of skin diseases account for most visits to the physician, thousands of skin conditions have been described.[14] Classification of these conditions often presents many nosological challenges, since underlying etiologies and pathogenetics are often not known.[17][18] Therefore, most current textbooks present a classification based on location (for example, conditions of the mucous membrane), morphology (chronic blistering conditions), etiology (skin conditions resulting from physical factors), and so on.[19][20] Clinically, the diagnosis of any particular skin condition is made by gathering pertinent information regarding the presenting skin lesion(s), including the location (such as arms, head, legs), symptoms (pruritus, pain), duration (acute or chronic), arrangement (solitary, generalized, annular, linear), morphology (macules, papules, vesicles), and color (red, blue, brown, black, white, yellow).[21] Diagnosis of many conditions often also requires a skin biopsy which yields histologic information[22][23] that can be correlated with the clinical presentation and any laboratory data.[24][25][26]

  1. ^ a b Cite error: The named reference Lookingbill was invoked but never defined (see the help page).
  2. ^ Lippens S, Hoste E, Vandenabeele P, Agostinis P, Declercq W (April 2009). "Cell death in the skin". Apoptosis. 14 (4): 549–69. doi:10.1007/s10495-009-0324-z. PMID 19221876. S2CID 13058619.
  3. ^ a b c d Burns, Tony; et al. (2006) Rook's Textbook of Dermatology CD-ROM. Wiley-Blackwell. ISBN 1-4051-3130-6.
  4. ^ Paus R, Cotsarelis G (1999). "The biology of hair follicles". N Engl J Med. 341 (7): 491–7. doi:10.1056/NEJM199908123410706. PMID 10441606. S2CID 35532108.
  5. ^ Goldsmith, Lowell A. (1983). Biochemistry and physiology of the skin. Oxford University Press. ISBN 978-0-19-261253-3.
  6. ^ Fuchs E (February 2007). "Scratching the surface of skin development". Nature. 445 (7130): 834–42. Bibcode:2007Natur.445..834F. doi:10.1038/nature05659. PMC 2405926. PMID 17314969.
  7. ^ Fuchs E, Horsley V (April 2008). "More than one way to skin". Genes Dev. 22 (8): 976–85. doi:10.1101/gad.1645908. PMC 2732395. PMID 18413712.
  8. ^ a b c d Cite error: The named reference Fitz was invoked but never defined (see the help page).
  9. ^ Bolognia, Jean L; et al. (2007). Dermatology. St. Louis: Mosby. ISBN 978-1-4160-2999-1.
  10. ^ a b c Rapini, Ronald P (2005). Practical dermatopathology. Elsevier Mosby. ISBN 978-0-323-01198-3.
  11. ^ Grant-Kels JM (2007). Color Atlas of Dermatopathology (Dermatology: Clinical & Basic Science). Informa Healthcare. pp. 163. ISBN 978-0-8493-3794-9.
  12. ^ Ryan, T (1991). "Cutaneous Circulation". In Goldsmith, Lowell A (ed.). Physiology, biochemistry, and molecular biology of the skin (2nd ed.). New York: Oxford University Press. p. 1019. ISBN 978-0-19-505612-9.
  13. ^ Swerlick RA, Lawley TJ (January 1993). "Role of microvascular endothelial cells in inflammation". J. Invest. Dermatol. 100 (1): 111S–115S. doi:10.1038/jid.1993.33. PMID 8423379.
  14. ^ a b c d Lynch, Peter J (1994). Dermatology. Williams & Wilkins. ISBN 978-0-683-05252-7.
  15. ^ King, LS (1954). "What Is Disease?". Philosophy of Science. 21 (3): 193–203. doi:10.1086/287343. S2CID 120875348.
  16. ^ Bluefarb, Samuel M (1984). Dermatology. Upjohn Co. ISBN 978-0-89501-004-9.
  17. ^ Tilles G, Wallach D (1989). "[The history of nosology in dermatology]". Ann Dermatol Venereol (in French). 116 (1): 9–26. PMID 2653160.
  18. ^ Lambert WC, Everett MA (October 1981). "The nosology of parapsoriasis". J. Am. Acad. Dermatol. 5 (4): 373–95. doi:10.1016/S0190-9622(81)70100-2. PMID 7026622.
  19. ^ Jackson R (1977). "Historical outline of attempts to classify skin diseases". Can Med Assoc J. 116 (10): 1165–68. PMC 1879511. PMID 324589.
  20. ^ Copeman PW (February 1995). "The creation of global dermatology". J R Soc Med. 88 (2): 78–84. PMC 1295100. PMID 7769599.
  21. ^ Fitzpatrick, Thomas B; Klauss Wolff; Wolff, Klaus Dieter; Johnson, Richard R.; Suurmond, Dick; Richard Suurmond (2005). Fitzpatrick's color atlas and synopsis of clinical dermatology. McGraw-Hill Medical Pub. Division. ISBN 978-0-07-144019-6.
  22. ^ Werner B (August 2009). "[Skin biopsy and its histopathologic analysis: Why? What for? How? Part I]". An Bras Dermatol (in Portuguese). 84 (4): 391–5. doi:10.1590/S0365-05962009000400010. PMID 19851671.
  23. ^ Werner B (October 2009). "[Skin biopsy with histopathologic analysis: why? what for? how? part II]". An Bras Dermatol (in Portuguese). 84 (5): 507–13. doi:10.1590/S0365-05962009000500010. PMID 20098854.
  24. ^ Xiaowei Xu; Elder, David A; Rosalie Elenitsas; Johnson, Bernett L; Murphy, George E (2008). Lever's Histopathology of the Skin. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN 978-0-7817-7363-8.
  25. ^ Weedon's Skin Pathology, 2-Volume Set: Expert Consult - Online and Print. Edinburgh: Churchill Livingstone. 2009. ISBN 978-0-7020-3941-6.
  26. ^ David J DiCaudo; Dirk Elston MD; Dirk M Elston; Tammie Ferringer; Christine J Ko; Christine Ko MD; Steven Peckham; Whitney A High (2009). Dermatopathology. Philadelphia: Saunders. ISBN 978-0-7020-3023-9.