Photosensitivity is the amount to which an object reacts upon receiving
, especially
visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished,
photoallergy and
phototoxicity.
The photosensitive ganglion cells in the mammalian eye are a separate class of light-detecting cells from the photoreceptor cells that function in vision.
Skin reactions
Human medicine
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
Photosensitivity occurs in multiple species including
sheep,
bovine, and
. 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)
[Jane C. Quinn; Yuchi Chen; Belinda Hackney; Muhammad Shoaib Tufail; Leslie A. Weston; Panayiotis Loukopoulos (2018), "Acute-onset high-morbidity primary photosensitisation in sheep associated with consumption of the Casbah and Mauro cultivars of the pasture legume biserrula", BMC Veterinary Research, doi:10.1186/s12917-017-1318-7] in sheep, or
buckwheat (green or dried) in horses.
[ buckwheat. Understanding Horse Nutrition.com]
In hepatogenous photosensitization, the photosensitzing substance is phylloerythrin, a normal end-product of chlorophyll metabolism.
See also
Notes
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