Photosensitivity

Not to be confused withphotosensitive epilepsyorphotophobia.Photosensitivityis the amount to which an object reacts upon receivingphotons, especiallyvisible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished,photoallergyandphototoxicity.[1][2]Thephotosensitive ganglion cellsin the mammalian eye are a separate class of light-detecting cells from thephotoreceptor cellsthat function in vision.Contents[hide] 1Skin reactions 1.1Human medicine 1.2Veterinary medicine 2Electronics 3Interpretation in chemistry 4See also 5External links 6NotesSkin reactions[edit]Human medicine[edit]Main article:Photosensitivity in humansSee also:phototoxicitySensitivity of theskinto a light source can take various forms. People with particular skin types are more sensitive tosunburn. Particular medications make the skin more sensitive to sunlight; these include most of thetetracycline antibiotics, heart drugsamiodarone, andsulfonamides. Particular conditions lead to increased light sensitivity. Patients withsystemic lupus erythematosusexperience skin symptoms after sunlight exposure; some types ofporphyriaare aggravated by sunlight. A rare hereditary conditionxeroderma pigmentosum(a defect in DNA repair) is thought to increase the risk of UV-light-exposure-related cancer by increasing photosensitivity.Veterinary medicine[edit]Main article:Photosensitivity in animalsPhotosensitivity occurs in multiple species includingsheep,bovine, andhorses.Photosensitizations are classified as primary if an ingested plant contains a photosensitive substance, likehypericininSt John's wortpoisoning in sheep, orbuckwheat plants(green or dried) in horses.[3]Inhepatogenous photosensitization, the photosensitzing substance isphylloerythrin, a normal end-product ofchlorophyllmetabolism.[4]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.Electronics[edit]Main article:PhotodetectorCertain electronic devices, such asphotodiodesandcharge-coupled devices, are designed to be sensitive to light. They are constructed to take advantage of thephotoelectric effect, the emission of electrons from matter upon the absorption ofelectromagnetic radiation. When light (one form of electromagnetic radiation) impinges on the active surface of such a device,electric currentflowing through orelectrical chargestored in the device will increase or decrease in proportion to the intensity andwavelengthof the light, although there is an upper limit to the amount of electrons released vs the increased intensity of the light, this comes out of quantum mechanics. This trait allows the device to perform regulating and sensing functions of many kinds. For example, aphotoresistorcircuitmay sense ambient light to turn on a street lamp at dusk.Digital camerasuse an array of photodiodes whose extreme sensitivity to light allows them to convert incoming photons into varying electrical charges with great accuracy. The varying charges are then encoded in abinary filewhich can be stored and later viewed on a computer screen or other medium.Interpretation in chemistry[edit]Chemicals that are photosensitive may undergochemical reactionswhen exposed to light. These chemicals, such ashydrogen peroxideand many prescription drugs, are stored in tinted or opaque containers until they are needed to prevent photodegradation. Devices that are photosensitive include the humanretinaandphotographic film(seefilm speedandsensitometry); their photosensitive materials undergo a chemical reaction when struck by light.Typical substances that are photosensitive arealkalisaltsandsilver halides.See also[edit] Heliotropism Photophobia Solar urticaria Snow blindnessExternal links[edit] FDA article- Chemical Photosensitivity: Another Reason to Be Careful in the Sun Toxic, Phototoxic and Sensitizing Essential Oils Sensor sensitivity (ISO) in digital cameras How to avoid overxposure to sunlight for the photosensitiveNotes[edit]1. Jump up^Anderson, D.M.; Keith, J.; Novac, P.; Elliott, M.A., ed. (1994).Dorland's Illustrated Medical Dictionary, 28th Edition. translated by. W. B. Saunders Company.ISBN0721655777.2. Jump up^JH Epstein (1999). "Phototoxicity and photoallergy".Seminars in cutaneous medicine and surgery18(4): 274284.PMID10604793.3. Jump up^Understanding Horse Nutrition.Com on buckwheat4. Jump up^D.C. Blood, J.A. Henderson, O.M. Radostits (1979).Veterinary Medicine(5th ed.). London: Baillire Tindall. pp.841847 (Lactation Tetany).ISBN0-7020-0718-8.