TONY CRADDOCK / SCIENCE PHOTO LIBRARY TONY CRADDOCK / SCIENCE PHOTO LIBRARY
Poison oak. This plant is a climbing vine which, together with poison ivy, is a variant of Toxicodendron radicans. These plants produce a toxic sap which contains the chemical urushiol. If touched, the antibodies of the body's immune system become sensitised to this chemical. The next time contact is made with this otherwise harmless sap, an aggressive immune response is triggered. Histamines are released, resulting in inflammation. While it is best to avoid the vine, antihistamine drugs and corticosteroid drugs will help to relieve the symptoms. Photographed in the USA.
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