Poison ivy is a common wild plant that causes an extremely irritating allergic reaction when you touch it or brush against it. Exposure to it may result in what doctors call contact dermatitis – a blistering rash that spreads over the skin in the area touched by the plant. In severe cases, this rash can develop into extremely painful, swollen areas of skin filled with fluid.
The rash usually appears within 2 days after exposure, but may take longer to appear with the first exposure. The rash peaks after 5 days, and begins to fade after a week or 10 days. While some people can become exposed and suffer little or no effect, being totally immune to poison ivy is unlikely. People who seem immune at one time and place may have an intense reaction the next time they encounter the plant. Poison ivy has 2 similarly nasty relatives: poison oak and poison sumac.