How to Identify Poison Ivy, Oak, and Sumac

Poison ivy, oak, and sumac facts

  • Many people are susceptible to the rashes of poison ivy, oak, and sumac.
  • The sap oil, called urushiol, causes the skin rash.
  • Poison ivy is not contagious.
  • Washing the oily sap from the skin with water and soap immediately can help prevent the rash.
  • Avoiding direct contact with the plants can prevent the rash.

What causes the rash? How do I identify poison ivy, oak, and sumac?

Poison ivy is a common cause of contact dermatitis, an allergic reaction to something that comes in direct contact with the skin. Allergic contact dermatitis as a response to plants is sometimes referred to as allergic phytodermatitis. This condition can be quite unpleasant but does not typically pose serious health risks. Prevention of the condition is best.

Poison ivy, oak and sumac are among the plants that produce a resin called an urushiol that can cause an allergic rash. These plants belong to the plant genus known as Toxicodendron. The plants are found in different geographical distributions and are present throughout the U.S. except for desert areas, higher elevations (above 4,000 feet), Alaska, and Hawaii. (Poison ivy is most common in the eastern U.S. and poison oak and sumac in the Southeast.) The signs and symptoms produced by each of these plants cannot be distinguished from one another by their appearance. In addition, the same urushiols are also found in the mango, cashew, and ginkgo 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, oak, or sumac

Both poison ivy and poison oak have three leaflets, while poison sumac more commonly displays leaflets of five, seven, or more that angle upward toward the top of the stem. Although it is often recommended that people learn to recognize the poison ivy plant ("Leaves of three, leave them be"), in practice, this can be difficult, since poison ivy and its relatives are often mixed in with other vegetation and not noticed until after the rash has begun. The leaves are shiny on their surface.

More than half the population can react to the poison ivy resin if they are exposed to it. Keeping the skin covered in situations in which exposure is hard to avoid is the best way to prevent the problem.

What are risk factors for poison ivy, oak, and sumac dermatitis?

Risk factors include being in outdoor areas where the plants may be present. These plants are present throughout the U.S., except for desert areas, higher elevations (above 4,000 feet), Alaska, and Hawaii. It has been estimated that most people have some degree of sensitivity to urushiol, but the degree of sensitivity varies among individuals.

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Medically reviewed by Avrom Simon, MD; Board Certified Preventative Medicine with Subspecialty in Occupational Medicine


Stephanides, Steven L., and Chris Moore. "Plant Poisoning, Toxicodendron." Aug. 18, 2009. <>.