It’s just scratching the surface to know that poison ivy (Toxicodendron radicans) causes a blistery itch. The sap, or oil, that poison ivy produces is called urushiol which is a mixture of phenolic compounds. Upon contact urushiol is absorbed by the skin within a few minutes where it chemically reacts with cell membranes and binds to them. Washing with soap and water soon after exposure to the poison ivy plant may prevent a skin reaction, but after the antigen is fixed it can neither be washed off nor is it contagious.
Urushiol is not really a poison at all. It does no damage of its own to tissues. The resulting dermatitis from exposure is the result of an allergic reaction which is nothing more than our immune system gone haywire. Once our bodies recognize urushiol as a foreign substance, special immune cells try to destroy it. This army of cells goes a little overboard with its protective reaction by releasing enzymes and protein toxins that disintegrate everything in the area. The result, worse case, is a red, oozing, itchy, painful mess. However, about 15-25% of people are not allergic and will not develop a reaction.
No other animal is sensitive to urushiol since they don’t share the complexity of the human immune system. Deer find poison ivy so delicious and nutritious that it may keep them from eating garden plants. Muskrats, cottontail rabbits and insects also munch the leaves and stems. The whitish-grey berry-like fruits are eaten by raccoons and many species of birds such as robins, catbirds, juncos, white-throated sparrows and pileated woodpeckers. Cardinals and goldfinches use rootlets from the vines to build their nests and the foliage provides shelter for many small animals.
Jewelweed (Impatiens capensis) is a poison ivy antidote which neutralizes urushiol. It often grows in the same areas as poison ivy when there is sufficient soil moisture. Jewelweed stem should be crushed and the liquid dabbed onto the skin at the place of contact and symptoms will not appear or be much less troublesome.
If only other things that irritate us had such a simple solution.