Poison ivy (Toxicodendron radicans) likes open disturbed areas but can be found in many habitats. Deer, cattle, goats, and other herbivores browse the nutritious foliage and birds eat the fruit. People fair poorly though as there are at least 10 million cases of allergic contact dermatitis in the United States each year from poison ivy, oak, and sumac
Urushiol and Sensitive People
While not a poison, these plants all contain clear, gummy oil called urushiol that causes an allergic reaction in most people; although, about 25% of us are essentially immune. Within minutes of contact, the urushiol begins chemically binding itself to skin cells. In sensitive people the body reacts by sending white blood cells that fill up the contact area and release cell-destroying toxins, thus producing blisters and sores.
Breathing and being in smoke from burning poison ivy can be especially bad because of contact with the lungs and large areas. An undamaged plant has no urushiol on its surface as the urushiol is in canals inside the leaves, stems and roots; however, the leaves are easily bruised and broken releasing the urushiol. Tools and clothes that contact the urushiol can transmit it months later because it is so persistent and does not dissolve in water.