Poison Ivy is native throughout the United States and much of southern Canada and can be found in a wide variety of locations including dry or wet woodlands, thickets, valleys, clearings, fence rows, roadsides and waste ground. It can appear as a bushy, erect or trailing shrub in sunny areas or as a woody climbing vine. The climbing vines have aerial rootlets. All parts of the plant contain a toxic oil called urushiol that causes significant and long-lasting skin irritations (allergic dermatitis) in most human beings. Infection can occur from direct contact with the plant, indirect contact (e.g., dog, rake or shoes) or from breathing smoke from a fire of plant material. Some humans seem to be immune.