Poison ivy is a common cause of contact dermatitis, an allergic reaction to something that comes in direct contact with the skin. This condition can be quite unpleasant but does not pose serious health risks. Prevention is better than treatment but can be hard to achieve.
Poison ivy is one of many plants that produce a resin called an urushiol that can cause an allergic rash. Related plants include the familiar poison oak and sumac, which are found in different geographical distributions. (Poison ivy is more common in the eastern U.S. and poison oak in the Southeast.) The rashes that each of these plants produce have a similar appearance. In addition, the same urushiols are also found in the mango, cashew, and gingko trees. In the case of mangos, peeling the fruit prevents dermatitis. People who press the whole fruit, including the rind, against their skin can develop a severe reaction around the mouth. Those downwind from burning vegetation containing one of the offending plants can also develop widespread allergic reactions.
Identifying poison ivy
Although it is often recommended that people learn to recognize the poison ivy plant ("Leaves of three, leave them be"), in practice, this is hard to do, since poison ivy and its relatives are often mixed in with other vegetation and not noticed until after the rash has begun. Keeping the skin covered in situations in which exposure is hard to avoid is the best way to prevent the problem.
More than half the population can react to the poison ivy resin if they are exposed to it.
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