{{Short description|Reaction to incoming photons}} {{other uses|photosensitive epilepsy|photophobia|flicker vertigo}} In medicine, '''photosensitivity''' is an abnormal reaction of the skin to light. There are two types: photoallergy and phototoxicity.<ref>{{cite book|editor1=Anderson, D.M. |editor2=Keith, J. |editor3=Novac, P. |editor4=Elliott, M.A. |year=1994|title=Dorland's Illustrated Medical Dictionary|edition=28th|publisher=W. B. Saunders Company|isbn=0721655777}}</ref><ref>{{cite journal|title=Phototoxicity and photoallergy|author=JH Epstein|year=1999|volume=18|issue=4|pages=274–284|journal=Seminars in Cutaneous Medicine and Surgery|pmid=10604793|doi=10.1016/s1085-5629(99)80026-1}}</ref> The photosensitive ganglion cells in the mammalian eye are a separate class of light-detecting cells from the photoreceptor cells that function in vision.
== Human medicine == {{main|Photosensitivity in humans}} {{see also|Phototoxicity}}
Sensitivity of the skin to a light source can take various forms. People with particular skin types are more sensitive to sunburn. Particular medications make the skin more sensitive to sunlight; these include most of the tetracycline antibiotics, heart drugs amiodarone, and sulfonamides. Some dietary supplements, such as St. John's Wort, include photosensitivity as a possible side effect.
Particular conditions lead to increased light sensitivity. Patients with systemic lupus erythematosus experience skin symptoms after sunlight exposure; some types of porphyria are aggravated by sunlight. A rare hereditary condition xeroderma pigmentosum (a defect in DNA repair) is thought to increase the risk of UV-light-exposure-related cancer by increasing photosensitivity.
== Veterinary medicine == {{main|Photosensitivity in animals}}
Photosensitivity occurs in multiple species including sheep, bovine, and horses. They are classified as primary if an ingested plant contains a photosensitive substance, like hypericin in St John's wort poisoning and ingestion of biserrula (''Biserrula pelecinus'')<ref>{{cite journal | author = Quinn Jane C., Chen Yuchi, Hackney Belinda, Shoaib Tufail Muhammad, Weston Leslie A., Loukopoulos Panayiotis | year = 2018 | title = "Acute-onset high-morbidity primary photosensitisation in sheep associated with consumption of the Casbah and Mauro cultivars of the pasture legume biserrula", ' | url = | journal = BMC Veterinary Research | volume = 14| issue = 1| article-number = 11 | doi = 10.1186/s12917-017-1318-7 | pmid = 29325550 | pmc = 5765607 | doi-access = free }}</ref> in sheep, or buckwheat plants (green or dried) in horses.<ref>{{usurped|1=[https://web.archive.org/web/20090628094941/http://www.understanding-horse-nutrition.com/buckwheat.html buckwheat]}}. Understanding Horse Nutrition.com</ref>
In '''hepatogenous photosensitization''', the photosensitzing substance is phylloerythrin, a normal end-product of chlorophyll metabolism. <ref>{{cite book |author1=D.C. Blood |author2=J.A. Henderson |author3=O.M. Radostits | title = Veterinary Medicine | publisher = Baillière Tindall | location = London | edition = 5th | year = 1979 | isbn = 0-7020-0718-8 | pages = 841–847 (Lactation Tetany)}}</ref> It accumulates in the body because of liver damage, reacts with UV light on the skin, and leads to free radical formation. These free radicals damage the skin, leading to ulceration, necrosis, and sloughing. Non-pigmented skin is most commonly affected.
==See also== * Digital camera ISO * Bergaptene * Heliotropism * Photophobia * Solar urticaria * Snow blindness * Photosensitizer
==Notes== {{reflist}}
==External links== {{Wiktionary}} * [http://www.lmscope.com/produkt22/Digital_Camera_Sensitivity_ISO_en.shtml Sensor sensitivity (ISO) in digital cameras]
{{Medical resources | DiseasesDB = | ICD10 = L56.8 | ICD9 = | ICDO = | OMIM = | MedlinePlus = | eMedicineSubj = | eMedicineTopic = | MeshID = }} {{Authority control}}
Category:Skin physiology Category:Clinical pharmacology