Poison ivy secretes an oil called urushiol that reacts to proteins in the human body. Contact of the oil with skin will cause inflammation, which can be painful and itchy. All parts of the plant but its pollen contain urushiol. Urushiol can persist for a long time -- sometimes for more than a year -- after it is brushed onto something, like clothes, soil or animals. It can even be carried by smoke from burning plants. The plant is of value to some animals. Birds eat the berries and insects found among the vines. Small mammals and deer eat the foliage, twigs and berries. Poison ivy is found throughout North America.