Sublingual bruises are usually caused by physiological factors, poor blood flow in the sublingual veins or pathologic factors such as varicose veins. As the mucous membrane under the tongue is relatively thin, and there are many blood vessels and nerves under the tongue, so the blood vessels of the sublingual veins can show a blue color through the mucous membrane, which is a normal phenomenon, when the blood vessels are deeper the sublingual veins are not obvious, and when the blood vessels are shallower the sublingual veins are more obvious. Pathologic factors of sublingual veins include poor blood flow in the sublingual veins, varicose veins, etc., and varicose veins of the sublingual veins have the risk of forming blood clots. If it is caused by physiologic factors, it may not need to be treated. If it is caused by pathological reasons, early medical treatment should be sought.