A bulge under the chin can be a locally enlarged lymph node. In many cases, it is caused by infection and should be treated systematically with anti-infection, especially if it occurs in the gums or mouth, and also with mouth rinsing, applying saline or metronidazole. If an abscess is formed, the patient will also have chills and high fever, and there is also a significant local inflammatory reaction, in which case surgery can be chosen for incision and drainage, with regular drug changes. Some patients have a thyroglossal cyst, which is a congenital developmental abnormality, manifesting as a swelling in the middle of the jaw with smooth surface and clear border, moving well with tongue extension movement, in which case surgery should be chosen promptly.