Poison ivy is a common plant that grows like weeds across the ground or like vines up a tree. Poison ivy contains urushiol, a type of oil that causes an allergic reaction in most people when it contacts the skin, causing a red, itchy rash. A poison ivy rash usually develops on the skin within one to two days after coming in contact with the plant, and begins as a red, swollen area that eventually develops blisters and starts to itch.
Poison ivy usually goes away on its own within a week, although larger affected areas may take longer to clear up. Patients can help relieve symptoms of poison ivy by using over-the-counter medications such as hydrocortisone cream, calamine lotion, antihistamines and oatmeal baths.