In most cases, a mild poison oak rash lasts for five to 12 days, according to WebMD. However, if the rash is severe, it can last up to 30 days.
Individuals experiencing a poison oak rash cannot cure it, but they can take measures to alleviate the symptoms. For example, taking cool showers and applying calamine lotion to the area can help. If the rash occurs in an area where mucus membranes are present - such as the groin - it is necessary to receive a steroid injection. This usually means prednisone. Approximately 75 percent of the American population has an allergic reaction to poison oak. It is one of the leading causes of plant related rashes in North America.