Contact with this annoying oil produces a rash in three out of four people. The rash can begin within a few hours after contact, or it can start three to five days later. These plants are a significant cause of workers' compensation claims in the United States. They are also the source of considerable distress to outdoor recreationists and hobbyists. The rash starts with itchiness and swelling, followed by a reddish inflammation of tiny pimples.
Blisters then form and couple in a chain-like reaction.
A clear fluid oozes from the blisters. This fluid then hardens to a yellowish crust. Avoid further contact with the plant oil if possible. In severe cases, a physician can prescribe antihistamine creams, tablets, or shots. No, the blisters are the body's natural allergic reaction to poison oak and poison ivy plants.