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Poison Ivy

Bayou-Diversity (14 June 2020) At the same time President Thomas Jefferson sent Lewis and Clark to explore the Missouri and Columbia Rivers he commissioned William Dunbar to conduct a similar expedition on the Ouachita River from its mouth to the legendary Hot Springs in present day Arkansas. Dunbar’s mandate was similar to Meriwether Lewis’ in that he was required to record and describe native plants and wildlife observed during the journey. One passage in his journal reads, “We have a Vine called the poison vine, from a property it possesses of affecting some persons passing near it, by causing an inflammation of the face resembling an Erysipelas. Other persons may handle this vine with impunity. It is believed perhaps without reason, that some are affected by only looking at it.”

Fortunately you can’t get poison ivy by just looking at it although for some folks it doesn’t seem to take much more than that. Poison ivy is one of three plants in our region that cause a contact dermatitis in many people. It is a vine that grows to fifty feet or more and has characteristic three lobed leaves. It is found in all habitat types. Much less common are poison oak, a small shrub which grows only in dry pineland soils and poison sumac, a small tree with divided leaves containing up to eleven leaflets. All are in the cashew family.

These plants contain a poisonous oil called urushiol. When it comes in contact with the skin the chemicals cause an immune reaction producing redness, itching and blistering. It is important to remember that you don’t have to touch the plant to have a reaction. The oil can be carried on the fur of pets, on garden tools or sports equipment, or on any object that has come in contact with the plant. It can even be transmitted in the smoke of burning poison ivy vines. In spite of what your mother said though, it can’t be spread by scratching the blisters.

Sensitivity to poison ivy is not something we are born with. It develops only after several encounters with the plants. Studies have shown that approximately 85 percent of the population will develop an allergic reaction if exposed to it. Sensitivity varies from person to person. Although they are not sure why, scientists believe that an individual’s sensitivity changes with time and tends to decline with age. Those who were once allergic may lose their sensitivity later in life.

Fruits of these poisonous plants are consumed by many kinds of wildlife without any apparent ill effects. Deer relish poison ivy leaves and concentrate the toxin in their chambered stomachs creating an occupational hazard for careless biologists who sometimes must examine them during herd health checks. This I can vouch for personally.

As usual, prevention is the best cure. Know how to recognize the poisonous plants and avoid them. If you are exposed, wash with cold running water as soon as possible. See a doctor for intense cases. (Adapted from Bayou-Diversity: Nature & People in the Louisiana Bayou Country by Kelby Ouchley; LSU Press)


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