Photosensitivity
Encyclopedia
Photosensitivity is the amount to which an object reacts upon receiving photon
s, especially visible light.
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. 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.
Photosensitivity is a well-known condition in different animals species including sheep, bovine, horse
. Its economic importance derives from the numerous animals involved in the same time.
Photosensitizations are classified as primary if an ingested plant contains a photosensitive substance, like hypericin
in St John's wort
poisoning 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.
s, are designed to be sensitive to light. They are constructed to take advantage of the photoelectric effect
, the emission of electrons from matter upon the absorption of electromagnetic radiation
. When light (one form of electromagnetic radiation) impinges on the active surface of such a device, electrical current flowing through or electrical charge stored in the device will increase or decrease in proportion to the intensity and wavelength
of 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, a photoresistor
circuit
may sense ambient light to turn on a street lamp at dusk. Digital cameras use charge-coupled devices 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 a binary file
which can be stored and later viewed on a computer screen or other medium.
s when exposed to light. These chemicals, such as hydrogen peroxide
and many prescription drugs, are stored in tinted or opaque containers until they are needed to prevent photodegradation. Devices that are photosensitive include the human retina
and photographic film
; their photosensitive materials undergo a chemical reaction when struck by light.
Typical substances that are photosensitive are alkali
salts and silver halide
s.
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s, especially visible light.
Human medicine
Sensitivity of the skinSkin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...
to a light source can take various forms. People with particular skin types are more sensitive to sunburn
Sunburn
A sunburn is a burn to living tissue, such as skin, which is produced by overexposure to ultraviolet radiation, commonly from the sun's rays. Usual mild symptoms in humans and other animals include red or reddish skin that is hot to the touch, general fatigue, and mild dizziness. An excess of UV...
. Particular medications make the skin more sensitive to sunlight; these include most of the tetracycline antibiotics
Tetracycline antibiotics
Tetracyclines are a group of broad-spectrum antibiotics whose general usefulness has been reduced with the onset of bacterial resistance. Despite this, they remain the treatment of choice for some specific indications....
, heart drugs amiodarone
Amiodarone
Amiodarone is an antiarrhythmic agent used for various types of tachyarrhythmias , both ventricular and supraventricular arrhythmias. Discovered in 1961, it was not approved for use in the United States until 1985...
, and sulfonamides. Particular conditions lead to increased light sensitivity. Patients with systemic lupus erythematosus
Systemic lupus erythematosus
Systemic lupus erythematosus , often abbreviated to SLE or lupus, is a systemic autoimmune disease that can affect any part of the body. As occurs in other autoimmune diseases, the immune system attacks the body's cells and tissue, resulting in inflammation and tissue damage...
experience skin symptoms after sunlight exposure; some types of porphyria
Porphyria
Porphyrias are a group of inherited or acquired disorders of certain enzymes in the heme bio-synthetic pathway . They are broadly classified as acute porphyrias and cutaneous porphyrias, based on the site of the overproduction and accumulation of the porphyrins...
are aggravated by sunlight. A rare hereditary condition xeroderma pigmentosum
Xeroderma pigmentosum
Xeroderma pigmentosum, or XP, is an autosomal recessive genetic disorder of DNA repair in which the ability to repair damage caused by ultraviolet light is deficient. In extreme cases, all exposure to sunlight must be forbidden, no matter how small. Multiple basal cell carcinomas and other skin...
(a defect in DNA repair) is thought to increase the risk of UV-light-exposure-related cancer by increasing photosensitivity.
Veterinary medicine
- See Photosensitivity in animalsPhotosensitivity in animalsPhotosensitivity is an abnormal skin reaction to direct sunlight exposure. It is unrelated to a sunburn. These reactions are due to photosensitization, the accumulation of photosensitive compounds beneath the skin. In some cases, the photodynamic substances come from ingested plants or drugs, after...
Photosensitivity is a well-known condition in different animals species including sheep, bovine, horse
Horse
The horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
. Its economic importance derives from the numerous animals involved in the same time.
Photosensitizations are classified as primary if an ingested plant contains a photosensitive substance, like hypericin
Hypericin
Hypericin is a naphthodianthrone, a red-colored anthraquinone-derivative, which, together with hyperforin, is one of the principal active constituents of Hypericum . Hypericin is believed to act as an antibiotic and non-specific kinase inhibitor...
in St John's wort
St John's wort
St John's wort is the plant species Hypericum perforatum, and is also known as Tipton's Weed, Chase-devil, or Klamath weed....
poisoning in sheep, or buckwheat plants
Buckwheat
Buckwheat refers to a variety of plants in the dicot family Polygonaceae: the Eurasian genus Fagopyrum, the North American genus Eriogonum, and the Northern Hemisphere genus Fallopia. Either of the latter two may be referred to as "wild buckwheat"...
(green or dried) in horses.
In hepatogenous photosensitization, the photosensitzing substance is phylloerythrin, a normal end-product of chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
metabolism. It accumulates in the body because of liver damage.
Interpretation in electronic engineering
Certain electronic devices, such as photodiodes and charge-coupled deviceCharge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
s, are designed to be sensitive to light. They are constructed to take advantage of the photoelectric effect
Photoelectric effect
In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...
, the emission of electrons from matter upon the absorption of electromagnetic radiation
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
. When light (one form of electromagnetic radiation) impinges on the active surface of such a device, electrical current flowing through or electrical charge stored in the device will increase or decrease in proportion to the intensity and wavelength
Wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of 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, a photoresistor
Photoresistor
A photoresistor or light dependent resistor is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor or CdS device, from "cadmium sulfide," which is the material from which the device is made and that actually exhibits the...
circuit
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...
may sense ambient light to turn on a street lamp at dusk. Digital cameras use charge-coupled devices 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 a binary file
Binary file
A binary file is a computer file which may contain any type of data, encoded in binary form for computer storage and processing purposes; for example, computer document files containing formatted text...
which can be stored and later viewed on a computer screen or other medium.
Interpretation in chemistry
Chemicals that are photosensitive may undergo chemical reactionChemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s when exposed to light. These chemicals, such as hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
and many prescription drugs, are stored in tinted or opaque containers until they are needed to prevent photodegradation. Devices that are photosensitive include the human retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
and photographic film
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
; their photosensitive materials undergo a chemical reaction when struck by light.
Typical substances that are photosensitive are alkali
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
salts and silver halide
Silver halide
A silver halide is one of the compounds formed between silver and one of the halogens — silver bromide , chloride , iodide , and three forms of silver fluorides. As a group, they are often referred to as the silver halides, and are often given the pseudo-chemical notation AgX...
s.
See also
- HeliotropismHeliotropismHeliotropism is the diurnal motion of plant parts in response to the direction of the sun.It is found in some members of family Malvacea e.g Malva or Lavetara...
- PhotophobiaPhotophobiaPhotophobia is a symptom of abnormal intolerance to visual perception of light. As a medical symptom photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical photosensitivity of the eyes, though the term...
- Photosensitivity in animalsPhotosensitivity in animalsPhotosensitivity is an abnormal skin reaction to direct sunlight exposure. It is unrelated to a sunburn. These reactions are due to photosensitization, the accumulation of photosensitive compounds beneath the skin. In some cases, the photodynamic substances come from ingested plants or drugs, after...
- Solar urticariaSolar urticariaSolar urticaria is a rare condition in which exposure to ultraviolet or UV radiation, or sometimes even visible light, induces a case of urticaria or hives that can appear in both covered and uncovered areas of the skin. It is classified as a type of physical urticaria. The classification of...
- Snow blindnessSnow blindnessPhotokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet rays from either natural or artificial sources. Photokeratitis is akin to a sunburn of the cornea and conjunctiva, and is not usually noticed until several...
External links
- FDA article - Chemical Photosensitivity: Another Reason to Be Careful in the Sun
- Toxic, Phototoxic and Sensitizing Essential Oils