Noise exposure, diseases, certain medications and aging can destroy parts of the inner ear and cause permanent hearing loss. Once damaged, the inner ear cannot be repaired. With sensorineural hearing loss, the entire cochlea is seldom damaged. If a sound is loud enough, a person with inner ear damage may hear something. The undamaged parts of the cochlea transmit sound to the auditory nerve and on to the brain, however the sound may be distorted.
Distortion occurs when the cochlea changes the sound in some way.
Sensorineural hearing loss is also characterized by a lower tolerance to loud sounds. Sensorineural hearing loss usually affects the high frequencies the most, which impairs a persons ability to differentiate consonant sounds. When a person has both a conductive hearing loss and a sensorineural hearing loss, it is called a mixed hearing loss. For example, if a child who has a permanent sensorineural hearing loss gets a middle ear infection, the effects of the two types of hearing loss combine to create a greater hearing loss. When a person has a sensorineural hearing loss, particularly a unilateral hearing loss, the problem may be beyond the inner ear, somewhere in the brainstem.