Urushiol

Urushiol
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 mixture of organic compounds with allergenic properties found in plants of the family Anacardiaceae, especially Toxicodendron spp. (e.g., poison oak, Chinese 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 (漆, 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.

Characteristics

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 ethanol, diethyl ether, and benzene.[8]

Urushiol is a mixture of several closely related organic compounds. Each consists of a catechol substituted in the 3 position with a hydrocarbon 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 urushiol contains chiefly catechols with C17 side-chains,[9] 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 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. It is important to do this quickly, 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]

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.[14]

Mechanism of action

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 hapten, leading to a type IV hypersensitive reaction.[15]

See also

References

  1. ↑ Cruse, Julius M.; Lewis, Robert E. (2003). Atlas of Immunology, Second Edition. CRC Press. p. 375. ISBN 978-1-4200-3994-8.
  2. ↑ "Can Reaction to Poison Ivy Cause Mango Allergy?". American College of Allergy, Asthma and Immunology. Retrieved 2014-06-02.
  3. ↑ "Urushiol: Human Health Effects". NIH. Retrieved 2014-06-02.
  4. ↑ Rietschel, Robert L.; Fowler, Joseph F.; Fisher, Alexander A. (2008). Fisher's Contact Dermatitis. PMPH-USA. p. 407. ISBN 978-1-55009-378-0.
  5. ↑ Appleby, Maia (Aug 2013). "Mango & Skin Rashes". Livestrong. Retrieved 2014-06-02.
  6. ↑ Tilton, Buck (2004). Wilderness First Responder: How to Recognize, Treat, and Prevent Emergencies in the Backcountry. Globe Pequot. ISBN 0-7627-2801-9.
  7. ↑ Oxford English Dictionary
  8. ↑ Hawley's Condensed Chemical Dictionary (14th ed.). John Wiley & Sons. 2002.
  9. ↑ Hogan, C. Michael (2008). Stromberg, Nicklas, ed. "Western poison-oak: Toxicodendron diversilobum". GlobalTwitcher. Archived from the original on 2009-07-21. Retrieved 2009-07-21.
  10. 1 2 3 McGovern, Thomas; Barkley, Theodore (1998). "Botanical Dermatology". International Journal of Dermatology. 37: 321–334. doi:10.1046/j.1365-4362.1998.00385.x.
  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. 128: 1460–1469. doi:10.1038/sj.jid.5701199.
  12. ↑ Rietschel, Robert L.; Fowler, Joseph F.; Fisher, Alexander A. (2008). Fisher's Contact Dermatitis. PMPH-USA. p. 408. ISBN 978-1-55009-378-0. Retrieved 2010-07-26.
  13. ↑ Barceloux, Donald G. (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 2010-07-26.
  14. ↑ Arney, Kat (13 June 2017). "Urushiol". Education in Chemistry. Vol. 54 no. 4. Royal Society of Chemistry. p. 8. Retrieved 19 June 2018.
  15. ↑ "Forget 'Polytetrafluoroethene', Pentadecacatechol is where it's at". 2012-07-11. Retrieved 2014-09-22.
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