Poison ivy produces an oily sap called urushiol throughout the plant. Exposure to that oil causes an allergic reaction in about 85% of people. Urushiol is extremely durable and can remain on clothing, fur, or tools for long periods after initial exposure. If you’re exposed to it, wash thoroughly with cool water and a degreasing soap, then use rubbing alcohol and scrub under the fingernails with a brush, and wash all the exposed clothing. Poison ivy can also be extremely toxic if inhaled, so the plant should never be burned.