Spoiler Poison ivy, poison oak, and poison sumac and other similar plants release an oil, urushiol, when the leaf or other plant parts are bruised, damaged, or burned. When the oil gets on the skin an allergic reaction, referred to as contact dermatitis, occurs in most exposed people as an itchy red rash with bumps or blisters. When exposed to 50 micrograms of urushiol, an amount that is less than one grain of table salt, 80 to 90 percent of adults will develop a rash.
Spoiler I am allergic to this stuff and whenever I see these members of the Anacardiaceae family it gets ripped out and destroyed. Poison ivy is plantis nongratus in our yard. As for poison oak and poison sumac, they do not exist in my yard but would be equally unwelcome. Jerry
Poison ivy, Poison Oak, Poison Sumac all produce a skin irritant called urushiol. Touching these plants will cause an allergic reaction, usually in the form of an itchy rash on the skin.