Poison ivy dermatitis is one of the most common forms of acute contact dermatitis seen in the dermatology office. A streaky, itching, blistering rash occuring during the summer is often caused by poison ivy, poison oak, or poison sumac. The oil in the sap, called urushiol, causes the rash. A person may become allergic to the oil at any time. Typically, an allergic reaction develops 1 to 3 days after contacting any part of the plant, an exposed pet, or clothing/gardening tools that have contacted the oil. The rash is not contagious, but different areas of the body may break out for weeks as areas that have received smaller amounts of exposure react more slowly to the urushiol oil. Over the counter hydrocortisone creams and lotions may relieve mild outbreaks of poison ivy. More severe outbreaks are treated with prescription medications such as strong topical or oral steroids. Ivy Block® lotion, which prevents the binding of the urushiol oil to the skin may help to prevent the rash of poison ivy in persons likely to be exposed to the plant. It is available without a prescription at most pharmacies.