Is poison ivy really poisonous?

A popular summer-camp rhyme is “Leaves of three, let it be.” Poison ivy, the three-leaved plant that grows wild in all regions of the United States, is aggravating to the skin, though not lethal if swallowed unless you are very allergic. After brushing up against the Poison ivy plant, a red rash usually develops. Rubbing the rash will not spread poison ivy to other parts of the body (or to another person) unless urushiol oilthe sticky, resin-like substance that causes the rashhas been left on your hands. Other plants that usually irritate the skin upon contact include cowhage, poison oak, poison sumac, rengas tree, and trumpet vine.

“Leaves of three, let it be,” is an easy rhyme to remember to identify poison ivy.