Red streaks on the legs may be caused by swelling lines, artificial urticaria and other reasons. 1. Expansion lines: often occur in the abdomen, thigh area, mostly due to a short period of rapid weight gain, the collagen fibers and elastic fibers below the skin tissue degeneration, fracture, so there is a red crack-like changes, resulting in red stripes on the legs. 2. Artificial urticaria: also called skin scratching sign, such as scratching or scratching the skin of the thigh with a blunt instrument, a few minutes later, stripes can appear along the scratches, may or may not have itching sensation, and most of them will subside after half an hour by themselves. Red streaks appear on the legs recommend timely hospitalization, clear cause of the disease under the guidance of the doctor for symptomatic treatment.