Gua Sha on the back is generally caused by heavy dampness, stagnation of qi and blood stasis (due to blood stasis caused by the lack of qi) or imbalance of yin and yang qi and blood. 1. If the back of the gua sha is red, may be due to scraping gua sha time is longer, or the technique is heavier, so that the skin is stimulated or microcirculation obstacles caused by the skin stasis aggravation, appear back of the gua sha. 2. If the back of the gua sha is dark purple, it may be a long time sitting or by the outside world cold damp stimulation or body dampness is heavy, caused by the phenomenon of blood circulation is not smooth. 3. If the back of the gua sha is dark purple or black purple, may be the body of the evil is heavier, there is stagnation of blood stasis, or internal organs of the yin and yang qi and blood imbalance, in the scraping of gua sha will also appear in the skin with a deep purple or black purple phenomenon. This situation, according to the color of gua sha under the guidance of the doctor for treatment, do not blindly operate on their own.