Hello, I'm Dr. Roy Benorach. I'm a pediatrician in private practice in Roswell, Ga. near Atlanta. My practice is named Pediatric Physicians, PC. And we're here on About.com to talk about identifying rashes caused by poison oak.Poison oak causes a rash called a contact dermatitis, which is essentially an allergic reaction in the skin. It looks like little blisters and bubbles, often in streaks and lines where a plant bushed against the skin. You'll see it most on skin that isn't covered by clothes, and also around the face and neck where skin is thinnest. Exposures on the skin of the hands don't usually trigger a rash, because the skin there is thick, but often people touch around their eyes and face, so they end up with more of a rash there on the thinner skin. The rash is very itchy, and usually becomes noticeable several hours or a day after the exposure -- it isn't immediate.The same rash can occur after exposure to poison oak, poison ivy, and poison sumac, and sometimes after exposures to mango trees or Ginkgo Biloba. Which plant is a more common trigger depends on where you live. Poison ivy is found thoughout the USA, poison oak is mostly found along the Pacific coast, and poison sumac is found in wet, swampy areas in the Eastern USA.