Photosensitivity is the amount to which an object reacts upon receiving

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...

s, especially

visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...

. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and

phototoxicity Phototoxicity, also called photoirritation, is a chemically induced skin irritation, requiring light, that does not involve the immune system. It is a type of photosensitivity. The skin response resembles an exaggerated sunburn. The involved chemi ...

. The

photosensitive ganglion cell Intrinsically photosensitive retinal ganglion cells (ipRGCs), also called photosensitive retinal ganglion cells (pRGC), or melanopsin-containing retinal ganglion cells (mRGCs), are a type of neuron in the retina of the mammalian eye. The presence ...

s 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 Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different de ...

to a light source can take various forms. People with particular skin types are more sensitive to

sunburn Sunburn is a form of radiation burn that affects living tissue, such as skin, that results from an overexposure to ultraviolet (UV) radiation, usually from the Sun. Common symptoms in humans and animals include: red or reddish skin that is h ...

. Particular medications make the skin more sensitive to sunlight; these include most of the

tetracycline antibiotics Tetracyclines are a group of broad-spectrum antibiotic compounds that have a common basic structure and are either isolated directly from several species of ''Streptomyces'' bacteria or produced semi-synthetically from those isolated compounds. T ...

, heart drugs

amiodarone Amiodarone is an antiarrhythmic medication used to treat and prevent a number of types of cardiac dysrhythmias. This includes ventricular tachycardia (VT), ventricular fibrillation (VF), and wide complex tachycardia, as well as atrial fibril ...

, and sulfonamides. Some dietary supplements, such as

St. John's Wort ''Hypericum perforatum'', known as St. John's wort, is a flowering plant in the family Hypericaceae and the type species of the genus ''Hypericum''. Possibly a hybrid between ''Hypericum maculatum, H. maculatum'' and ''Hypericum attenuatum, H. ...

, 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 Porphyria is a group of liver disorders in which substances called porphyrins build up in the body, negatively affecting the skin or nervous system. The types that affect the nervous system are also known as acute porphyria, as symptoms are ...

are aggravated by sunlight. A rare hereditary condition

xeroderma pigmentosum Xeroderma pigmentosum (XP) is a genetic disorder in which there is a decreased ability to repair DNA damage such as that caused by ultraviolet (UV) light. Symptoms may include a severe sunburn after only a few minutes in the sun, freckling in su ...

(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 Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus '' Ovis'', in everyday usage it almost always refers to domesticated ...

bovine Bovines (subfamily Bovinae) comprise a diverse group of 10 genera of medium to large-sized ungulates, including cattle, bison, African buffalo, water buffalos, and the four-horned and spiral-horned antelopes. The evolutionary relationship betwe ...

, and

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...

s. They are classified as primary if an ingested plant contains a photosensitive substance, like

hypericin Hypericin is a naphthodianthrone, an anthraquinone derivative which, together with hyperforin, is one of the principal active constituents of '' Hypericum'' ( Saint John's wort). Hypericin is believed to act as an antibiotic, antiviral and non- ...

St John's wort ''Hypericum perforatum'', known as St. John's wort, is a flowering plant in the family Hypericaceae and the type species of the genus '' Hypericum''. Possibly a hybrid between '' H. maculatum'' and '' H. attenuatum'', the species can be found ...

poisoning and ingestion of biserrula (''Biserrula pelecinus'') in sheep, or buckwheat plants (green or dried) in horses. In hepatogenous photosensitization, the photosensitzing substance is phylloerythrin, a normal end-product of chlorophyll metabolism. 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.

Notes

External links

Sensor sensitivity (ISO) in digital cameras
{{Authority control Skin physiology Clinical pharmacology

Skin reactions

Human medicine

Veterinary medicine

See also

Notes

External links