Back scraping appear bruise purple have two aspects of the reason, one is belong to scraping after the normal phenomenon of gua sha, the second is due to scraping strength is too big or time is too long or the patient coagulation function abnormality lead to subcutaneous small blood vessels bleeding abnormally caused. 1. normal phenomenon: gua sha therapy is to use the edge of the smooth tool, dipped in oil and other media in the skin for repeated scraping operation, local repeated mechanical stimulation will cause subcutaneous small blood vessel bleeding, bruise point, called gua sha point. After scraping the skin appeared gua sha point, play blood circulation, strengthen the role of local blood circulation. In general, it will gradually subside in 3-5 days. 2. when scraping gua sha is too strong or too long: if scraping gua sha is too strong or long time local repeated mechanical stimulation, it will cause subcutaneous small blood vessel damage bleeding or subcutaneous tissue damage, subcutaneous small blood vessel structure damage make blood overflow subcutaneous form bruise purple. 3. coagulation function abnormality: if the patient exists coagulation function abnormality, such as thrombocytopenia, coagulation factor deficiency, or due to take some anticoagulant drugs lead to coagulation function weakening, then gua sha operation is more likely to cause subcutaneous bruises. Scraping operation need professional doctor operation, do not operate by yourself, scraping strength should not be too big, time should not be too long. If the back scratching phenomenon, need to go to the hospital in a timely manner to clarify the cause, by the doctor according to the situation of individualized treatment program, so as not to delay the condition.