R = (CH2)14CH3 or
R = (CH2)7CH=CH(CH2)5CH3 or
R = (CH2)7CH=CHCH2CH=CH(CH2)2CH3 or
R = (CH2)7CH=CHCH2CH=CHCH2CH=CH2 and others

Urushiol /ʊˈrʃi.ɒl/ 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 parts of the mango tree .[1][2][3][4][5]

In most individuals, urushiol causes an allergic skin rash on contact,[6] known as urushiol-induced contact dermatitis.

The name urushiol is derived from the Japanese word for the lacquer tree, Toxicodendron vernicifluum ( urushi).[7] 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.[8] 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,[9] 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.[10]

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.[10] After absorption into 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, and the T-lymphocytes cause pathology through the production of cytokines and cytotoxic damage to the skin.[11]

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.[10][12][13]

Mechanism of action

A video describing the mechanism of action for poison ivy and other such plants containing urushiol

Dermatitis is mediated by an induced immune response. Urushiol acts as a hapten, leading to a Type IV hypersensitive reaction.[14]

See also


  1. Julius M. Cruse, MD; Robert E. Lewis (2010). Atlas of Immunology, Second Edition. CRC Preess. pp. 464–. ISBN 978-0-8493-9489-8. Retrieved June 2014. Check date values in: |access-date= (help)
  2. "Can Reaction to Poison Ivy Cause Mango Allergy?". American College of Allergy, Asthma, and Immunology. Retrieved June 2014. Check date values in: |access-date= (help)
  3. "Urushiol: Human Health Effects". NIH. Retrieved June 2014. Check date values in: |access-date= (help)
  4. Alexander A. Fisher (2007). Fisher's Contact Dermatitis. Pmph Usa. pp. 862–. ISBN 978-0-8493-9489-8. Retrieved June 2014. Check date values in: |access-date= (help)
  5. Appleby, Maia (Aug 2013). "Mango & Skin Rashes". Livestrong. Retrieved June 2014. Check date values in: |access-date= (help)
  6. Buck Tilton (2004) Wilderness First Responder: How to Recognize, Treat, and Prevent Emergencies in the Backcountry, Globe Pequot, 320 pages ISBN 0-7627-2801-9
  7. Oxford English Dictionary
  8. Hawley's Condensed Chemical Dictionary, 14th Edition, 2002, John Wiley & Sons, Inc.
  9. C. Michael Hogan (2008) Western poison-oak: Toxicodendron diversilobum, GlobalTwitcher, ed. Nicklas Stromberg
  10. 1 2 3 McGovern Tomas, Barkley Theodore (1998) "Review Botanical Dermatology", International Journal of Dermatology, vol 37, pp 321-334
  11. Gober D. Michael et al. (2008) "Human Natural Killer T Cells infiltrate into the Skin at Elicitation Sites of Allergic Contact Dermatitis" Journal of investigative Dermatology, vol 128, pp1460-1469
  12. Robert L. Rietschel; Joseph F. Fowler; Alexander A. Fisher (2008). Fisher's contact dermatitis. PMPH-USA. pp. 408–. ISBN 978-1-55009-378-0. Retrieved 26 July 2010.
  13. Donald G. Barceloux (2008). Medical Toxicology of Natural Substances: Foods, Fungi, Medicinal Herbs, Plants, and Venomous Animals. John Wiley and Sons. pp. 681–. ISBN 978-0-471-72761-3. Retrieved 26 July 2010.
  14. "Forget "Polytetrafluoroethene", Pentadecacatechol is where it's at". 11 Jul 2012. Retrieved 22 Sep 2014.
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