Phototoxins are toxins that can cause allergic reactions in particularly susceptible individuals and which can cause dangerous photosensitivity in a much broader range of subjects.
A toxin is a poisonous substance produced within living cells or organisms; synthetic toxicants created by artificial processes are thus excluded. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived from the word toxic.
Photosensitivity is the amount to which an object reacts upon receiving photons, 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.
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Phototoxins are common in:
- a variety of plants (including food plants where they may be a biological defence):
- many citruses contain essential oils that are photosensitizers;
- some herbal remedies (notably St John's wort, though incident rates for this plant are reportedly low);
- the carrot family of Apiaceae; [1] [2]
Herbalism is the study of botany and use of plants intended for medicinal purposes. Plants have been the basis for medical treatments through much of human history, and such traditional medicine is still widely practiced today. Modern medicine makes use of many plant-derived compounds as the basis for evidence-based pharmaceutical drugs. Although herbalism may apply modern standards of effectiveness testing to herbs and medicines derived from natural sources, few high-quality clinical trials and standards for purity or dosage exist. The scope of herbal medicine is sometimes extended to include fungal and bee products, as well as minerals, shells and certain animal parts.
Hypericum perforatum, known as perforate St John's-wort, common Saint John's wort and St John's wort, is a flowering plant in the family Hypericaceae. Although used as a medicinal herb with possible antidepressant activity, high-quality clinical evidence for such effects is limited. The plant is poisonous to livestock.
Apiaceae or Umbelliferae is a family of mostly aromatic flowering plants named after the type genus Apium and commonly known as the celery, carrot or parsley family, or simply as umbellifers. It is the 16th-largest family of flowering plants, with more than 3,700 species in 434 genera including such well-known and economically important plants such as ajwain, angelica, anise, asafoetida, caraway, carrot, celery, chervil, coriander, cumin, dill, fennel, hemlock, lovage, cow parsley, parsley, parsnip and sea holly, as well as silphium, a plant whose identity is unclear and which may be extinct.
- some prescribed medications (such as tetracycline antibiotics); and
- many essential oils, perfumes and cosmetics.
In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the population during that process. Thirdly, it is a phenotypic trait or adaptive trait, with a functional role in each individual organism, that is maintained and has evolved through natural selection.
Citrus is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes.
An essential oil is a concentrated hydrophobic liquid containing volatile chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetherolea, or simply as the oil of the plant from which they were extracted, such as oil of clove. An essential oil is "essential" in the sense that it contains the "essence of" the plant's fragrance—the characteristic fragrance of the plant from which it is derived. The term essential used here does not mean indispensable as with the terms essential amino acid or essential fatty acid which are so called since they are nutritionally required by a given living organism. In contrast to fatty oils, essential oils typically evaporate completely without leaving a stain or residue.
Ingested medications may cause systemic photosensitivity and topically applied medications, cosmetics and essential oils may lead to local (or perhaps systemic) photosensitivity. Para-aminobenzoic acid (PABA), found in some sunscreens, can also cause photosensitivity.
4-Aminobenzoic acid (also known as para-aminobenzoic acid or PABA because the number 4 carbon in the benzene ring is also known as the para position) is an organic compound with the formula H2NC6H4CO2H. PABA is a white solid, although commercial samples can appear gray. It is slightly soluble in water. It consists of a benzene ring substituted with amino and carboxyl groups. The compound occurs naturally.
Upon exposure to light, notably light containing ultraviolet radiation, discolouration of the skin (whether as inflammation, lightening or darkening) or rashes may result. In extreme cases, blistering may also occur.
Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and contributes about 10% of the total light output of the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.
