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. Patients are encouraged to not scratch the blisters, as bacteria from your fingers may lead to an infection.