# Photosensitivity

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> Source: https://en.wikipedia.org/wiki/Photosensitivity
> Source revision: 1328570688
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{{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](/source/photoallergy) and [phototoxicity](/source/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 cell](/source/photosensitive_ganglion_cell)s in the mammalian eye are a separate class of light-detecting cells from the [photoreceptor cell](/source/photoreceptor_cell)s that function in vision.

== Human medicine ==
{{main|Photosensitivity in humans}}
{{see also|Phototoxicity}}

Sensitivity of the [skin](/source/skin) to a light source can take various forms. People with particular skin types are more sensitive to [sunburn](/source/sunburn). Particular medications make the skin more sensitive to sunlight; these include most of the [tetracycline antibiotics](/source/tetracycline_antibiotics), heart drugs [amiodarone](/source/amiodarone), and [sulfonamides](/source/Sulfonamide_(medicine)).
Some dietary supplements, such as [St. John's Wort](/source/St._John's_Wort), include photosensitivity as a possible side effect.

Particular conditions lead to increased light sensitivity. Patients with [systemic lupus erythematosus](/source/systemic_lupus_erythematosus) experience skin symptoms after sunlight exposure; some types of [porphyria](/source/porphyria) are aggravated by sunlight. A rare hereditary condition [xeroderma pigmentosum](/source/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](/source/sheep), [bovine](/source/bovine), and [horse](/source/horse)s. They are classified as primary if an ingested plant contains a photosensitive substance, like [hypericin](/source/hypericin) in [St John's wort](/source/Hypericum_perforatum) 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](/source/buckwheat) (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](/source/phylloerythrin), a normal end-product of [chlorophyll](/source/chlorophyll) metabolism.&nbsp;<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](/source/Digital_camera_ISO)
* [Bergaptene](/source/Bergaptene)
* [Heliotropism](/source/Heliotropism)
* [Photophobia](/source/Photophobia)
* [Solar urticaria](/source/Solar_urticaria)
* [Snow blindness](/source/Snow_blindness)
* [Photosensitizer](/source/Photosensitizer)

==Notes==
{{reflist}}

==External links==
{{Wiktionary}}
* [http://www.lmscope.com/produkt22/Digital_Camera_Sensitivity_ISO_en.shtml Sensor sensitivity (ISO) in digital cameras]

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Category:Skin physiology
Category:Clinical pharmacology

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Adapted from the Wikipedia article [Photosensitivity](https://en.wikipedia.org/wiki/Photosensitivity) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Photosensitivity?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.