A lump in the left jaw may be caused by enlarged lymph nodes, enlarged salivary glands under the jaw, and trauma. 1. Enlarged lymph nodes: when patients have enlarged lymph nodes, they may have lumps in the left jaw. Patients with enlarged lymph nodes are usually accompanied by symptoms such as skin redness, swelling, pressure and pain, and even breakout. 2. Enlarged submandibular salivary glands: If the patient has enlarged submandibular salivary glands, the salivary gland ducts will be easily blocked, which may cause a lump in the left jaw. Usually such patients are also accompanied by periapical abscess, tongue pain and tongue numbness and other symptoms. 3. Trauma: If the left jaw is hit or violent, it will easily lead to subcutaneous bruising, resulting in soft tissue injury, and the symptoms of lumps in the left jaw may occur, accompanied by pain. Patients with lumps in the left jaw should go to the hospital in time, improve the examination to clarify the cause of the disease, and then follow the doctor’s instructions for treatment.