" If you spend time in the outdoors, you are susceptible to poison ivy, oak, and sumac. The oil found in these plants causes an itchy, blistering rash to form on the skin 12 to 72 hours after you come in contact with it. The rash is not contagious and may appear to spread but this is actually just a delayed reaction. Without treatment, the rash will typically go away in a few weeks. The skin ...