Pain on one side of the ear and no pain on the other side may be caused by trauma, acute otitis externa and otitis media on one side of the ear. 1. Trauma: If the patient has recently bruised one ear or fallen and hit one ear, it may lead to pain on one side of the ear and no pain on the other side of the ear, which may be accompanied by swelling, bruising and other symptoms. 2. Acute otitis externa: Usually, otitis externa is related to decreased resistance of the skin of the external auditory canal and pathogen infection. If one side of the patient suffers from acute otitis externa, it can cause one side of the ear pain phenomenon. 3. Otitis media: mainly caused by pathogen infection, Eustachian tube dysfunction and other causes of middle ear infection. When the patient suffers from otitis media on one side of the ear, it can be manifested as pain on one side of the ear, accompanied by hearing loss, discharge of purulent secretion from the ear canal and other symptoms. When the patient has pain in one ear and no pain in the other, it is recommended that the patient consult a doctor in time for diagnosis and treatment.