Poison ivy, poison oak and poison sumac are plants that grow in wooded areas all over North America. While they have the name poison, the plants aren’t actually poisonous. Instead, they all contain a sticky oil called urushiol that causes an itchy rash once it brushes up against your skin. The rash caused by these plants usually appears 24-72 hours after contact and lasts for about a week. Each rash is slightly different, depending on the plant. Once the oil is thoroughly washed off affected skin and clothing, the rash itself cannot spread on its own. However, because of the time delay between exposure and rash, it can appear as if the rash is spreading, when this effect is actually due to the exposure from 24-72 hours prior. If you believe you have a rash due to contact with one of these plants, it is best to get an evaluation and treatment to help relieve some of the uncomfortable symptoms.