Poison oak skin rashes can be identified by contact dermatitis, an itchy, red rash, according to WebMD. It is caused by urushiol, the sticky oil contained in poison oak.
When someone brushes up against poison oak leaves, flowers, stems, roots or berries, the urushiol oil causes an allergic reaction. This can also happen if someone touches anything that has come into contact with poison oak. The resulting rash is characterized by symptoms such as redness or red streaks, itching, raised areas or small bumps, and blisters which may ooze fluid. Some people may experience more severe symptoms such as large, oozing blisters, swelling and breathing trouble. In this case, medical attention should be sought right away, according to WebMD.