Poison ivy, poison oak, and poison sumac are plants that cause a rash in those allergic to them. This rash is caused by a chemical in the sap. About 50%-70% of people are sensitized to this chemical and are, therefore, allergic. Virtually everyone will eventually become sensitized if repeatedly exposed.

Poison Ivy Rash
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The allergic reactions to poison ivy, oak, and sumac occur when sensitized people come in contact with urushiol oil. This oil is found in the roots, stems, leaves, and fruit of the plant. This oil is released if the plant is damaged or bruised.

If not washed, oil from these plants may stay potent for years on clothing, tools, toys, and other items, especially in dry conditions.