The left side of the face muscle pain is considered to be related to temporomandibular joint disorder, oral diseases, mumps, shingles and other causes. 1. Temporomandibular joint disorder: such as having been hit by external forces, opening the mouth too wide, often chewing hard food, having the habit of unilateral chewing, excessive wear and tear of the teeth, missing too many grinding teeth and other factors can lead to temporomandibular joint disorder. This can lead to localized soreness and pain, and then popping and movement disorders, which are most obvious when chewing and opening the mouth. 2. Oral diseases: such as gingivitis and pulpitis, which cause facial swelling and facial muscle pain on the affected side. In this case, it is recommended to go to the stomatology department to clarify the cause of the disease and carry out targeted treatment. 3. Mumps: usually caused by bacterial or viral infection. Symptoms such as enlarged lymph nodes in the jaw, enlargement of the parotid gland and fever can occur. At the same time, it can also cause soreness in the facial muscles. 4. Herpes zoster: In most cases, facial swelling as well as pain in the facial muscles occurs after the onset of herpes zoster. However, in a few cases, facial muscle pain or swelling occurs before the occurrence of shingles. There are many reasons for the symptoms, and it is recommended to go to the hospital for examination and treatment in time to avoid delaying the condition. At the same time, you should pay attention to the combination of work and rest, regular work and rest, adequate rest, and avoid staying up late.