Facial muscles are innervated by the facial nerve, so the appearance of facial stiffness and numbness is considered to be caused by facial neuritis or facial nerve injury. For example, stimulation of the face by cold or prolonged exertion, resulting in low body immune function, can induce facial neuritis and facial stiffness, as well as symptoms such as crookedness of the mouth and incomplete eye closure. If there has been a head injury, resulting in a skull base fracture, which causes damage to the facial nerve, it can also lead to the above symptoms. Intracranial tumors, especially auditory neuroma and meningioma of the pontocerebellar horn region, also often cause the above symptoms. Acute cerebrovascular diseases, such as cerebral infarction and cerebral hemorrhage, also tend to leave sequelae of the above symptoms.