What does "triangle" mean?

Danger triangle is an isosceles triangle area on human face, with the root of nasal bone as the vertex and the connecting line of two angles as the bottom. It includes the upper and lower lips, the nose and the main front organs on both sides of the alar.

The danger triangle is dangerous because the blood supply in this area is particularly rich. The arterial blood supplied to the face becomes venous blood after metabolism. The venous blood of the face is injected into the internal jugular vein and flows back to the heart through the anterior facial vein, posterior facial vein, maxillary vein and ophthalmic vein. These veins have branches on the face, forming a dense vascular network and communicating with each other. The anterior facial vein communicates with the ophthalmic vein in the inner canthus, and the posterior facial vein communicates with the anterior facial vein in the depth of the lateral pterygoid muscle through the pterygoid plexus at the beginning of the maxillary vein. The ophthalmic vein and pterygoid plexus directly communicate with cavernous sinus, which is a reticular structure composed of intracranial capillary network. Secondly, compared with venous vessels in other parts of the body, facial venous vessels lack a device to prevent blood from flowing back-venous valve.

Once the dangerous triangle is infected, it is easy to cause inflammation to spread to the whole face. If blood with bacteria flows back to the brain, it will cause intracranial infection and endanger life.