The consequences of contact with poison ivy can be severe. Urushiol, the oil from this itch-causing plant, can trigger an allergic reaction and cause an uncomfortable rash. Like its close cousins — poison sumac and poison oak — poison ivy can create some itchy days. Urushiol oil is extremely potent and can last for a long time. As MNN has reported, “Only 1 nanogram ofurushioloil — a billionth of a gram — is needed to cause a reaction. The oil stays active for one to five years on a dead plant.” And if the oil gets on your clothes and is transferred to your skin, you are exposed. Experts at poison-ivy.org urge people to throw away their clothes if they have been exposed to the plant. And if the clothing is too precious to toss, they urge you to wash it twice before wearing.