Urushiol is responsible for the agonizing itch caused by poison ivy.
Layman's explanation:Urushiol is a yellow oil comprised of a mixture of organic compounds containing a catechol (1,2-hydroxy benzene) and a pentadecyl or heptadecyl side chain; some side chains may be unsaturated. The earliest use of urushiol was in the art of ancient Asia, where works of art were coated in lacquer finishes derived from the trees Toxicodendron vernicifluum or Rhus verniciflua. In fact, the name urushiol is derived from urushi, the Japanese word for the lacquer prepared from the sap of the Japanese lacquer tree ("kiurushi"). During the lacquering process, the phenols oxidize and polymerize with the help of enzymes to yield a coating that is hard and resistant to mechanical stress. Inhabitants of North America are familiar with the more malevolent side of urushiol-as the active ingredient of poison ivy and poison oak. Most people are highly allergic to urushiol and will develop redness, painful itching, and blistering of the skin if they touch even minute amounts of the oil. Interestingly, one of the most effective remedies for poison ivy comes also from a plant. The Jewelweed plant (Impatiens capensis) found in North American hardwood forests produces a chemical called Lawsone (a naphthoquinone) with antihistamine and anti-inflammatory properties that lessen the effects of urushiol on the skin.
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