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 ( /ʊˈruːʃi.ɒl/) is an oily organic allergen found in plants of the family Anacardiaceae, especially Toxicodendron spp. (e.g., poison oak, poison ivy, poison sumac). It causes an allergic skin rash on contact,[1] known as urushiol-induced contact dermatitis. The name comes from the Japanese word Kiurushi[2] which denotes a lacquer produced in East Asia from the sap of Toxicodendron vernicifluum (the Lacquer Tree). 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 and Japanese lacquerwares.
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Urushiol is a pale-yellow liquid with density of 0.968 and a boiling point of 200–210 °C. It is Soluble in alcohol, ether, and benzene.[3] 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; urushiol oil is a mixture of saturated and unsaturated molecules. The mixture varies with the vegetative species. Whereas western poison oak urushiol contains chiefly catechols with C17 side-chains,[4] poison ivy and poison sumac yield mostly catechols with C15 side-chains. The allergic reaction is dependent on the degree of unsaturation of the alkyl chain. Less than half of the general population reacts with the saturated urushiol alone, but over 90% react with urushiol containing at least two degrees of unsaturation (double bonds). Moreover longer side chains tend to produce stronger sensitizers. [5] This suggests that the allergic contact dermatitis is caused by Van der Waals' forces.[6] Before Urushiol has been absorbed by the skin it can be removed with water. However, time is of great importance as 50% of urushiol is absorbed in 10min. Once Urushiol has penetrated into the skin, attempting to remove with water is inefficient. [7] Once urushiol has been absorbed by the skin it is recognized by dendritic cells called langerhans cells that are part of the immune system, these cells then migrate to 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 by producing cytokines and cytotoxic damage to the skin. [8]
The urushiol liquid is an oleoresin contained within the sap of poison ivy and related plants, and after injury to the plant or during late fall, the sap leaks to the surface of the plant, where the urushiol becomes a blackish lacquer after contact with oxygen.[9][10][11]