There are purple marks at the root of the thigh, and this is most likely a swelling stripe. The purple streaks may appear after a longer period of time, and when they first form, they are usually a red streak. These streaks are formed mainly because the body grows too fast, or suddenly the body weight increases in a short period of time, which causes the skin to grow too fast, but the subcutaneous tissue does not grow effectively in time, especially the collagen fibers and elastic fibers can not keep up in time, so it may cause the degeneration of collagen fibers and elastic fibers, and eventually appear to break. On the surface, a red crack-like appearance is seen, which is what we usually call swelling lines, also known as atrophy lines.