Blisters can form as part of your body's natural reaction to the resin (urushiol) from poison ivy and oak plants. A rash can last anywhere from 1-2 weeks, or up to 30+ days in more severe cases. It is best not to pop the blisters to avoid a potential infection, and let them run their course naturally. If you've had an active rash for 2 weeks with little to no success with over-the-counter treatments, we recommend contacting your physician.