The upper lip is in the triangle, the facial danger triangle, which usually refers to the triangle formed by the connection between the two sides of the mouth and the nasal root. Why is it called a dangerous area? This is related to the unique anatomy and physiology of oral and maxillofacial region. The superficial facial veins include facial veins and superficial temporal veins. The valves of facial veins are poorly developed, few in number and fragile, and they are not completely closed. Usually, in the case of muscle contraction, blood can go backwards. When facial inflammation occurs, especially when there is infection in this triangle, it is easy to form thrombus in the anterior vein, which affects the normal venous blood return and returns to the superior ophthalmic vein, causing the cavernous sinus on both sides of the intracranial sella to spread facial inflammation to the skull, resulting in serious complications such as cavernous sinus suppuration and thrombophlebitis. Once complications occur, eyelid edema, congestion in the throat, exophthalmos, abduction limitation, ptosis and even visual impairment usually occur. Inflammation can also spread to the eyes and surrounding tissues, as well as chills, fever, headache and so on. It may happen all over the body. In severe cases, even septicemia and toxemia may occur, which is life-threatening. Remember, don't scratch, squeeze or prick pus in the dangerous triangle of the face, or you will regret it.