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Urushiol is an oily mixture of
organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s with
allergenic An allergen is a type of antigen that produces an abnormally vigorous immune response in which the immune system fights off a perceived threat that would otherwise be harmless to the body. Such reactions are called Allergy, allergies. In technic ...
properties found in
plants Plants are predominantly photosynthetic Photosynthesis is a process used by plants and other organisms to Energy transformation, convert light energy into chemical energy that, through cellular respiration, can later be released to fuel t ...

plants
of the
family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same Politic ...
Anacardiaceae The Anacardiaceae, commonly known as the cashew family or sumac family, are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social gro ...
, especially ''
Toxicodendron ''Toxicodendron'' is a genus of flowering plants in the sumac family, Anacardiaceae. It contains trees, shrubs and woody plant, woody vines, including Toxicodendron radicans, poison ivy, poison oak, and the lacquer tree. All members of the genus ...
'' ''spp.'' (e.g.,
poison oakPoison oak refers to two plant species in the genus ''Toxicodendron,'' both of which can cause skin irritation: *''Toxicodendron diversilobum'' or Western poison oak, found in western North America *''Toxicodendron pubescens'' or Atlantic poison oak ...
, Chinese lacquer tree,
poison ivy
poison ivy
,
poison sumac
poison sumac
) and also in parts of the
mango A mango is an edible stone fruit ), showing both fruit In botany, a fruit is the seed-bearing structure in flowering plants (also known as angiosperms) formed from the ovary after flowering. Fruits are the means by which angiosper ...

mango
tree. In most individuals, urushiol causes an allergic
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 cuticle, animal coverings, such as the arthropod exoskeleton, have differ ...

skin
rash on contact, known as
urushiol-induced contact dermatitis Urushiol-induced contact dermatitis (also called Toxicodendron dermatitis or Rhus dermatitis) is a type of allergic contact dermatitis caused by the oil urushiol found in various plants, most notably species of the genus ''Toxicodendron'': poison i ...
. The name urushiol is derived from the
Japanese Japanese may refer to: * Something from or related to Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white rectangle , image_coat = Imperial Seal of J ...

Japanese
word for the lacquer tree, . The
oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

oxidation
and polymerization of urushiol in the tree's sap in the presence of moisture allows it to form a hard
lacquer Lacquer is a type of hard and potentially shiny coating A coating is a covering that is applied to the surface of an object, usually referred to as the substrate Substrate may refer to: Physical layers *Substrate (biology), the natural e ...

lacquer
, which is used to produce traditional Chinese, Korean and Japanese
lacquerware Lacquerware are objects decoratively covered with lacquer. Lacquerware includes small or large containers, tableware, a variety of small objects carried by people, and larger objects such as furniture and even coffins painted with lacquer. Befor ...

lacquerware
.


History

Although urushiol-containing
lacquer Lacquer is a type of hard and potentially shiny coating A coating is a covering that is applied to the surface of an object, usually referred to as the substrate Substrate may refer to: Physical layers *Substrate (biology), the natural e ...

lacquer
s and their skin-irritating properties were well known in East Asia for several millennia, its first recorded western texts were in 1624 by John Smith and he initially likened the plant to
English Ivy ''Hedera helix'', the common ivy, English ivy, European ivy, or just ivy, is a species of flowering plant of the Hedera, ivy genus in the family (biology), family Araliaceae, native plant, native to most of Europe and western Asia. A rampant, cli ...

English Ivy
. He did not classify it as a poison at first due to the speed with which its rash disappeared and Smith hypothesized that there may actually be medicinal uses for the plant. In the 18th and 19th centuries, many experiments were done in this area to determine whether or not this theory was true. Because that era's medicinal culture was dominated by plant-based treatments, physicians were hopeful that the strong effect this chemical produced on the body could be effective in some way. André-Ignace-Joseph Dufresnoy was one of the first to come up with a medicinal use for this chemical in 1780 when he boiled poison ivy to produce an infusion for internal use. This led to a distilled extract of poison ivy which he prescribed to many people suffering from skin problems and even paralysis. He claimed this treatment to have yielded several positive results. For many years, poison ivy was thought to fall into the '
Rhus Sumac ( or ), also spelled sumach, is any of about 35 species of flowering plants in the genus ''Rhus'' and related genera in the cashew family (Anacardiaceae). Sumacs grow in Subtropics, subtropical and temperate regions throughout the world, in ...
' genus; however, in the 1900s, it was reclassified into a more appropriate genus, '
Toxicodendron ''Toxicodendron'' is a genus of flowering plants in the sumac family, Anacardiaceae. It contains trees, shrubs and woody plant, woody vines, including Toxicodendron radicans, poison ivy, poison oak, and the lacquer tree. All members of the genus ...
,' meaning ''poison tree''. There were many documented cases of irritations and allergic reactions from the plant, and its propensity for medicinal use quickly dwindled. After this new categorization, scientists began attempts to determine what it was that rendered plants of this genus noxious, starting with a hypothesis of a volatile oil present in the plants. While this proved incorrect, Rikou Majima from Japan was able to determine that the chemical urushiol was the irritant. Further, he determined that the substance was a type of alkyl catechol, and due to its structure it was able to penetrate the skin and survive on surfaces for months to years. Urushiol's ability to polymerise into a hard glossy coating is the chemical basis for traditional lacquerware in many Asian countries. After urushiol comes in contact with oxygen, under certain conditions it become a black lacquer and has been named Urushi lacquer.


Characteristics

Urushiol in its pure form is a pale-yellow
liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned with the motions of physical objects, ...

liquid
with a
specific gravity Relative density, or specific gravity, is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemon ...
of 0.968 and a
boiling point The boiling point of a substance is the temperature at which the vapor pressure 280px, The ''pistol test tube'' experiment. The tube contains alcohol and is closed with a piece of cork. By heating the alcohol, the vapors fill in the space, inc ...
of . It is soluble in
diethyl ether Diethyl ether, or simply ether, is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

diethyl ether
,
acetone Acetone, or propanone, is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, ...

acetone
,
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), ...

ethanol
,
carbon tetrachloride Carbon tetrachloride, also known by many other names (such as tetrachloromethane, also recognised by the IUPAC, carbon tet in the cleaning industry Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and ...

carbon tetrachloride
, and
benzene Benzene is an organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come from a once-living organi ...

benzene
. Urushiol is a mixture of several closely related
organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
s. Each consists of a
catechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is a toxic organic compound with the molecular formula C6H4(OH)2. It is the ''ortho'' isomer In chemistry Chemistry is the scientific discipline involved with Chemical e ...

catechol
substituted in the 3 position with a
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
chain that has 15 or 17 carbon atoms. The hydrocarbon group may be saturated or unsaturated. The exact composition of the mixture varies, depending on the plant source. Whereas
western poison oak ''Toxicodendron diversilobum'' (syn. ''Rhus diversiloba''), commonly named Pacific poison oak or western poison oak, is a woody vine or shrub in the sumac family, Anacardiaceae. It is widely distributed in western North America, inhabiting conife ...
urushiol contains chiefly catechols with C17 side-chains, poison ivy and poison sumac contain mostly catechols with C15 sidechains. The likelihood and severity of allergic reaction to urushiol is dependent on the degree of unsaturation of the
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
chain. Less than half of the general population experience a reaction with the saturated urushiol alone, but over 90% do so with urushiol that contains at least two degrees of unsaturation (double bonds). Longer side chains tend to produce a stronger reaction. Urushiol is an
oleoresinOleoresins are semi-solid extracts composed of resin In polymer chemistry and materials science The interdisciplinary field of materials science, also commonly termed materials science and engineering, covers the design and discovery of ne ...

oleoresin
contained within the sap of and related plants, and after injury to the plant, or late in the fall, the sap leaks to the surface of the plant, where under certain temperature and humidity conditions the urushiol becomes a blackish
lacquer Lacquer is a type of hard and potentially shiny coating A coating is a covering that is applied to the surface of an object, usually referred to as the substrate Substrate may refer to: Physical layers *Substrate (biology), the natural e ...

lacquer
after being in contact with
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
. Urushi lacquer is very stable. It is able to withstand disturbances from alkali, acid, and alcohol, while also being able to resist temperatures of over 300 °C. However, the lacquer can be degraded by UV rays from the sun and other sources. Within the United States, urushiol-containing plants are distributed throughout. Poison ivy can be found in all states except California, Alaska, and Hawaii. Poison Oak can be found on the west coast or some states in the southeast, while poison sumac can be found only in the eastern half of the country. These plants all have distinguishing features that will help in identification. Poison ivy always grows with three shiny, pointy leaves. Poison oak has a similar look, but with larger and more rounded leaves that are hairy and grow in groups of 3, 5, or 7. Poison sumac grows in groups of 7 to 13 leaves, but always in an odd number. The leaves are feather-shaped and shiny.


Allergic response and treatment

Before the urushiol has been absorbed by the skin, it can be removed with soap and water. Substantial amounts of urushiol may be absorbed within minutes. Once urushiol has penetrated the skin, attempting to remove it with water is ineffective. After being absorbed by the skin, it is recognized by the
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as Tumor immunology, cancer cells and objects such ...
's
dendritic cell Dendritic cells (DCs) are antigen-presenting cells (also known as ''accessory cells'') of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), an ...

dendritic cell
s, otherwise called
Langerhans cell Langerhans cells (LC) are tissue-resident macrophages Macrophages (abbreviated as MPhi, φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune ...
s. These cells then migrate to the
lymph nodes A lymph node, or lymph gland, is a kidney-shaped Organ (anatomy), organ of the lymphatic system, and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocy ...
, where they present the urushiol to
T-lymphocytes A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system, and play a central role in the adaptive immune response. T cells can be easily distinguished from other lymphocytes by the presence of a T- ...
and thus recruit them to the skin, and the T-lymphocytes cause pathology through the production of
cytokine Cytokines are a broad and loose category of small protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and ...

cytokine
s and
cytotoxic Cytotoxicity is the quality of being toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''o ...
damage to the skin. This causes the painful rash, blisters, and itching. Once this response starts, only a few treatments, such as
cortisone Cortisone is a pregnane (21-carbon) steroid hormone. Cortisone is a naturally-occurring corticosteroid metabolite that is also used as a pharmaceutical prodrug; it is not synthesized in the adrenal glands. Cortisol is converted by the action of ...

cortisone
or
prednisone Prednisone is a glucocorticoid medication mostly used to immunosuppressive drug, suppress the immune system and decrease inflammation in conditions such as asthma, COPD, and rheumatologic diseases. It is also used to treat high blood calcium du ...

prednisone
, are effective. Medications that can reduce the irritation include
antihistamine Antihistamines are drugs Uncoated tablets, consisting of about 90% acetylsalicylic acid, along with a minor amount of inert fillers and binders. Aspirin is a pharmaceutical drug often used to treat pain, fever, and inflammation. A drug i ...

antihistamine
s (
diphenhydramine Diphenhydramine is an antihistamine Antihistamines are drugs which treat allergic rhinitis and other allergies. Typically people take antihistamines as an inexpensive, generic, over-the-counter drug that can provide relief from nasal ...

diphenhydramine
(Benadryl) or
cetirizine Cetirizine, sold under the brand name Zyrtec among others, is a second-generation antihistamine used to treat allergic rhinitis (hay fever), dermatitis Dermatitis (also known as eczema) is inflammation of the skin Skin is the layer of u ...

cetirizine
(Zyrtec)). Other treatments include applying cold water or
calamine lotion Calamine, also known as calamine lotion, is a medication used to treat mild itchiness Itch (also known as pruritus or automatic tickle) is a sensation that causes the desire or reflex In biology Biology is the natural science that stud ...
to soothe the pain and stop the itching.


Mechanism of action

To cause an allergic dermatitis reaction, the urushiol is first oxidized to create two double-bonded oxygens on the chemical. It then reacts with a protein
nucleophile In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a ...

nucleophile
to trigger a reaction within the skin.
Dermatitis Dermatitis is inflammation of the Human skin, skin, typically characterized by itchiness, erythema, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become lichenification, thick ...

Dermatitis
is mediated by an induced immune response. Urushiol is too small a molecule to directly activate an immune response. Instead, it attaches to certain proteins of the skin, where it acts as a
haptenHaptens are small molecules that elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself (in general, only large molecules, infectious agents, ...

hapten
, leading to a type IV hypersensitive reaction.
Hydrocortisone Hydrocortisone is the name for the hormone cortisol when supplied as a medication. Uses include conditions such as adrenocortical insufficiency, adrenogenital syndrome, hypercalcemia, high blood calcium, thyroiditis, rheumatoid arthritis, derma ...
, the active ingredient in cortisone, works to alleviate this condition by stopping the release of chemicals that cause the dermatitis reaction. Hydrocortisone itself does not react with urushiol in any way.


See also

*
Anti-itch drugAntipruritics, also known as anti-itch drugs, are medications that inhibit the itching (Latin: ''pruritus'') often associated with sunburns, allergic reactions, eczema, psoriasis, chickenpox, Fungal infection in animals, fungal infections, insect bit ...
s, for treating the toxin. * Bentoquatam, a
barrier cream A barrier cream is a topical formulation used in industrial applications and as a cosmetic to place a physical barrier between the skin and contaminants that may irritate the skin (contact dermatitis or occupational dermatitis). There are many o ...
applied before exposure. *
Burow's solutionBurow's solution is an aqueous solution An aqueous solution is a solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute and the water ...
which can treat the symptoms of the rash caused by urushiol. * ''
Ginkgo biloba ''Ginkgo biloba'', commonly known as ginkgo or gingko ( ) also known as the maidenhair tree, is a species of tree native to China. It is the last living species in the order Ginkgoales Ginkgoales is a gymnosperm The gymnosperms ( Greek l ...

Ginkgo biloba
'' and
cashew The cashew tree (''Anacardium occidentale'') is a tropical evergreen tree that produces the cashew seed and the cashew apple pseudofruit. The tree can grow as high as , but the dwarf cultivars, growing up to , prove more profitable, with earlie ...

cashew
, plants containing chemicals closely related to urushiol. *
Hapten Haptens are small molecules that immunogenicity, elicit an immune response only when attached to a large carrier such as a protein; the carrier may be one that also does not elicit an immune response by itself (in general, only large molecules, infe ...

Hapten
, small molecules that can elicit an immune response under certain conditions. *
Mango tree ''Mangifera indica'', commonly known as mango, is a species of flowering plant in the sumac and poison ivy family Anacardiaceae. It is native to the Indian subcontinent where it is indigenous. Hundreds of Plant cultivation, cultivated variety (bot ...

Mango tree
s, which may cause cross-reaction allergies with urushiol.


References


Further reading

* * * * * * * *


External links


Poison Oak
at ''Wayne's Word''

* ttp://www.cattail.nu/ivy/ivy_index.html The Poison Ivy Tutorial {{authority control Catechols Resins