The culprit is urushiol, a sap-like oil found in the roots, stems, leaves, flowers and fruits of poison ivy that evolved as a chemical defense mechanism against herbivores and, perhaps, insects. Urishol is the defense mechanism of poison ivy to prevent infections. When urishol reacts with our protein cells, our bodies think they are strange and begin to attack, causing a rash. The plant species to which “poison ivy” belongs produces a defensive toxic vegetable oil called urushiol.
Poison ivy produces this oil to prevent pesky herbivores from feeding on its leaves. And despite being a nuisance to people, poison ivy is an important member of the ecosystem. Its leaves, stems and berries are food for animals, and its vines can provide shelter for small animals such as toads and mice, even helping them climb trees. Climate Change Is Benefiting Poison Ivy, Allowing Larger, More Irritating Plants.
Poison ivy and its relatives are common throughout the United States. The leaves of poison ivy are covered with a mixture of chemicals called urushiol. When people receive urushiol on the skin, it causes allergic contact dermatitis. This is a T-cell-mediated immune response, also called delayed hypersensitivity, in which the body's immune system recognizes as foreign and attacks the complex of urushiol derivatives with skin proteins.
The irony is that urushiol, in the absence of immune attack, would be harmless. The most common treatment for severe contact dermatitis is with corticosteroids, which decrease immune attack and resulting inflammation. A recent recommendation for mild cases is to use manganese sulfate solution to reduce itching. And while there are other native plants with three leaves, they don't show the same amount of variability in shape, says Jelesko.
It may take four hours to 10 days for the rash to appear, depending on how much urushiol comes into contact with your skin, how sensitive you are, and how many times you have been previously exposed to poison ivy. The mature Virginia vine has five leaflets; its stems have tendrils with thick pads at the end, but they lack the reddish roots that often cover poison ivy vines. Pell said: “It clings to the sand and the ground like along the dunes, where you see poison ivy on the way to the beach. Researchers who refer to ancient herbarium specimens in scientific collections have also had reactions to dried and pressed plants.
This innocent-looking plant produces an itch that “lets you appreciate how good your skin was before you touched it. Like its close relatives, poison oak and poison sumac, the plant is distinguished by the powerful skin irritant urushiol. Contact dermatitis induced by poison ivy is still common in North America, affecting about 50 million Americans each year. His fascination throughout his career with poison ivy is not based on a personal immunity to urushiol, the oily resin that is the active compound in all parts of the plant, from seed and leaf to woody vine, even when dormant.
Taxonomists often become emotionally attached to a particular species by maintaining their stature in the systematic hierarchy, even if that species is poison ivy. But the family Anacardiaceae also includes cashew nuts (its common name is the cashew family), as well as pistachios, mangoes and worthy garden subjects such as smoke trees (Cotinus) and Rhus, commonly called sumac (the genus of poison ivy was placed for a long time). If you've ever spent any time outdoors in the woods, working in the yard, even on the edges of a playground, you may have experienced something similar after you've found poison ivy. With so many new gardeners joining the fold this past year of the pandemic, presumably some are also having their first close encounters with poison ivy.