MICHAEL P. GADOMSKI / SCIENCE PHOTO LIBRARY MICHAEL P. GADOMSKI / SCIENCE PHOTO LIBRARY
Poison ivy (Toxicodendron radicans). Poison ivy grows as a vine or shrub, and is widespread in North America. It produces sap containing the chemical urushiol. If the plant is touched, the body's immune system can become sensitised to this chemical and the next time contact is made, an aggressive immune response is triggered. The main symptoms of poison ivy exposure are rashes, itching and blisters. Antihistamine and corticosteroid drugs help to relieve the symptoms. Photographed in the Pocono Mountains, Pennsylvania, USA.
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