Pain at the junction of the ear and face when opening the mouth may be caused by temporomandibular joint disorder syndrome, mumps, glossopharyngeal neuralgia and other diseases. 1. Temporomandibular joint disorder syndrome: the cause of this disease has not been elucidated, and studies have shown that it may be related to poor occlusion, trauma, stress, overload of the temporomandibular joint, inflammation, osteoarthropathy and other causes. The main symptom is the pain of the affected muscles when opening the mouth too wide, which can be manifested as pain at the junction of the ear and face when opening the mouth. 2. Mumps: This disease is caused by mumps virus infection, which can be transmitted through the respiratory tract, indirect contact, mother and child. Since the parotid gland is located at the junction of the ear and face, patients will have the symptom of pain at the junction of the ear and face when they open their mouths, and a few patients will also have symptoms such as headache and lack of appetite. 3. Hypoglossal neuralgia: the cause of this disease is still unclear, it may be caused by tumors around the pharyngeal nerve, inflammation and infection, or the lack of myelin sheath of the nerve root, which causes compression on blood vessels. Its typical symptom is pain in the distribution area of the glossopharyngeal nerve, which can spread from the back of the tongue, throat, etc. to the ears and the area behind the chin, so some patients will have pain at the junction of the ears and face when they open their mouths. There are many causes of pain at the junction of the mouth, ear and face, and it is necessary to go to the hospital to determine the specific cause.