Photosensitivity is the amount to which an object reacts upon receiving
photons, especially visible light.
Interpretation in medicine
Sensitivity of the
skinto 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 antibioticsand the heart drug amiodarone. Particular conditions lead to increased light sensitivity. Patients with systemic lupus erythematosusexperience skin symptoms after sunlight exposure; some types of porphyriaare aggravated by sunlight. All types of skin cancerare linked to excessive sunlight exposure, and the rare hereditary condition xeroderma pigmentosum(a defect in DNA repair) accelerates this risk manifold.
While the term "photoallergy" or "sunlight allergy" is commonly employed in many of the conditions mentioned, there is in fact no actual
allergyin the technical sense of the word if the reaction is a purely photoirritant type. Skin photoallergies occur when light is required to trigger the interaction between a chemical material in the skin and host tissues with the resultant formation of an antigen that is recognized by the host immune system. Typically, these types of reaction are similar to a hapten-carrier reaction in contact sensitization reactions with the exception that light is needed to trigger the binding of the hapten to the host carrier molecule.
Interpretation in electronic engineering
Certain electronic devices, such as
photodiodesand charge-coupled devices, 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 currentflowing through or electrical chargestored in the device will increase or decrease in proportion to the intensity and wavelengthof the light. This trait allows the device to perform regulating and sensing functions of many kinds. For example, a photoresistorcircuit may sense ambient light to turn on a street lamp at dusk. Digital camerasuse 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 filewhich can be stored and later viewed on a computer screen or other medium.
Interpretation in chemistry
Chemicals that are photosensitive may undergo
chemical reactions when exposed to light. These chemicals, such as hydrogen peroxideand many prescription drugs, are stored in tinted or opaque containers until they are needed to prevent photodegradation. Devices that are photosensitive include the human retinaand photographic film; their photosensitive materials undergo a chemical reaction when struck by light.
Typical substances that are photosensitive are
alkali saltsand silver halides.
Photosensitivity in animals
* [http://www.fda.gov/fdac/features/496_sun.html FDA article] - Chemical Photosensitivity: Another Reason to Be Careful in the Sun
* [http://candleandsoap.about.com/od/fragrancesandaromatherapy/a/toxicEO.htm Toxic, Phototoxic and Sensitizing Essential Oils]
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