
Toxicodendron Radicans distribution map
Poison ivy (toxicodendron radicans) is the most common of the urushiol producing plants in the eastern U.S. Contact with urushiol oil is the substance that causes an allergic rash in 90% of the population.
Even a tiny amount (1 nanogram, a billionth of a gram) of sticky, resin-like urushiol oil will case a skin reaction. 1/4 ounce of the potent oil would be enough to cause a rash on the entire population of the earth!
