Fact sheet on the signs of poison ivy poison oak and poison sumac and treatment of each. Employers and employees should take precautions when working in and around wooded areas and in heavy foliage, because they may come in contact with poison ivy, oak, or sumac. Approximately 90 percent of Americans are allergic to these plants that cause a bothersome rash and intense itching. Touching the stems, roots, or leaves of these plants results in direct contact of skin with urushiol (pronounced oo-roo-shee-ohl) oil, which causes the itching. The cause of the rash, blisters, and the infamous itch is from exposure to […]