R = (CH2)14CH3 or
R = (CH2)7CH=CH(CH2)5CH3 or
R = (CH2)7CH=CHCH2CH=CH(CH2)2CH3 or
R = (CH2)7CH=CHCH2CH=CHCH=CHCH3 or
R = (CH2)7CH=CHCH2CH=CHCH2CH=CH2 and others
Urushiol // is an oily organic allergen found in plants of the family Anacardiaceae, especially Toxicodendron spp. (e.g., poison oak, Lacquer Tree, poison ivy, poison sumac) and also in mangos.
The name urushiol is derived from the Japanese word for the lacquer tree, Toxicodendron vernicifluum (漆 urushi?). The oxidation and polymerization of urushiol in the tree's sap in the presence of moisture allows it to form a hard lacquer, which is used to produce traditional Chinese, Korean and Japanese lacquerware.
Urushiol is a pale-yellow liquid with a specific gravity of 0.968 and a boiling point of 200 °C (392 °F). It is soluble in alcohol, ether, and benzene. Urushiol is a mixture of several closely related organic compounds. Each consists of a catechol substituted with an alkyl chain that has 15 or 17 carbon atoms. The alkyl group may be saturated or unsaturated. The exact composition of the mixture varies, depending on the plant source. Whereas western poison oak urushiol contains chiefly catechols with C17 side-chains, poison ivy and poison sumac contain mostly catechols with C15 side-chains. The likelihood and severity of allergic reaction to urushiol is dependent on the degree of unsaturation of the alkyl 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. This suggests that the allergic contact dermatitis is caused by Van der Waals forces.
Before the urushiol has been absorbed by the skin, it can be removed with soap and water. However, time is of the essence, as 50% of the urushiol can be absorbed within 10 minutes. Once urushiol has penetrated into the skin, attempting to remove it with water is ineffective. Once absorbed by the skin it is recognized by the immune system's dendritic cells, otherwise called Langerhans cells. These cells then migrate to the lymph nodes, where they present the urushiol to T-lymphocytes and thus recruit them to the skin. Once in the skin, the T-lymphocytes cause pathology through the production of cytokines and cytotoxic damage to the skin.
Urushiol is an oleoresin contained within the sap of poison ivy 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 after being in contact with oxygen.
Mechanism of action
- Anti-itch drugs, for treating the toxin.
- Bentoquatam, a barrier creme applied before exposure.
- Burow's solution which can treat the symptoms of the rash caused by urushiol.
- Ginkgo biloba and cashew, plants containing chemicals closely related to urushiol.
- Hapten, the name of a wider class of allergens including urushiol.
- Mango trees, which may cause cross reaction allergies with urushiol.
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