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Risk Factors and Cause

Exposure to poison ivy, poison oak, and poison sumac can cause an allergic reaction. The characteristic itchy rash develops in response to contact with a substance called urushiol. This substance is present in the leaves, stems, and roots of the plants.

Reactions can occur following direct contact with the plant, through indirect contact (e.g., touching an object that has picked up urushiol from the plant, such as gardening tools and pet fur), and through airborne c...Read the full article