The Danger Triangle is dangerous first and foremost because this area has a particularly rich blood supply. The arterial blood that supplies the face is metabolized into venous blood. The venous blood of the face flows back to the heart mainly through the anterior facial vein, the posterior facial vein, the maxillary vein, the ophthalmic vein and the internal jugular vein. These veins branch off from each other in the face to form a dense network of blood vessels that communicate with each other. The anterior facial vein communicates with the ophthalmic vein at the medial canthus of the eye, and the posterior facial vein communicates with the anterior facial vein through the pterygoid plexus at the beginning of the maxillary vein at the depth of the external pterygoid muscle. The ophthalmic vein and the pterygoid plexus, in turn, communicate directly with the cavernous sinus, a meshwork of intracranial capillary networks. Secondly the facial veins lack a device to prevent backflow of blood - a venous valve - compared to those in other parts of the body.
An infection in the danger triangle can easily cause inflammation to spread throughout the face, and if the infected blood backs up and is injected into the skull, an intracranial infection can occur, which can be life-threatening.