Pain under the left ear can be clinically caused by the following possibilities: First, acute otitis externa, acute tympanitis, or acute otitis media can cause inflammation of the lymph nodes under the ear, resulting in a painful sensation, which is still a common clinical condition. Secondly, some patients have acute mumps, and the inflammation of the parotid gland causes pain and enlargement of the parotid gland, resulting in a painful sensation under the ear. Third, some patients have an acute inflammatory infection of the pharynx, and when the patient swallows, the pain in the pharynx radiates to the lower part of the ear, manifesting as a painful sensation under the ear. Fourth, some patients have neuralgia, which may be caused by fire, staying up late, etc.