It is very common for people to ask, "How long does a poison ivy last?", especially if they are new to having a breakout.  Unfortunately, there isn't a one-size-fits-all answer to this question. Typically, mild cases of poison ivy or poison oak rash can last 5-12 days. This will depend on how your individual body reacts to the urushiol from the plants. Some people are less sensitive, resulting in a mild rash which may clear up quickly. Hypersensitive people may have a severe rash that forms quickly and should see a doctor for proper treatment. In severe cases, poison ivy rash may last 30 days or longer.