Poison ivy, poison oak and poison sumac are all caused by uroshiol, an oil that is found in all three plants. Since the rash doesn’t appear for 12 to 72 hours, at first it can be hard to tell if you have it. If you think you’ve been exposed, immediately use medicated, poison ivy soap or a combination of water and alcohol to decrease or eliminate the oil. Once the rash develops, over the counter medications, including corticosteroid cream, drying agents such as calamine lotion, and antihistamines, can help with itching. The rash will go away on its own in two to three weeks. If the rash becomes too uncomfortable, see your primary care provider or dermatologist. A prescription steroid ointment or an oral steroid can help with itching. If scratching has caused an infection, an antibiotic may be needed. As with any allergies, if you have an extreme reaction to any of these plants, including difficulty breathing or swallowing, go directly to an emergency room.