The ear is made up of the outer, middle, and inner ear. The type of hearing loss you may have depends on what part (or parts) of your ear are damaged. Hearing tests by an audiologist can tell you which type you have and what the best treatment is for your type of hearing loss. There are three main types of hearing loss: sensorineural, conductive, and mixed. Auditory neuropathy spectrum disorder is a fourth type of hearing but is likely less common.
Sensorineural hearing loss
The inner ear helps with both hearing and balance. It contains fluid and thousands of tiny hair cells inside. We “hear” sound when these hair cells move, transforming the vibrations into electrical signals your brain interprets as sound. Different hair cells move with different sounds. When these hair cells or the hearing nerve itself are damaged, sensorineural hearing loss occurs. This is the most common form of hearing loss.
Sensorineural hearing loss is permanent because there is no way to repair the damaged hairs. It generally affects both ears, though not necessarily equally. Hearing aids are usually beneficial to patients with this type of hearing loss.
There are many causes of sensorineural hearing loss; however, aging and chronic exposure to noise are the biggest culprits. Most common causes include:
- Noise exposure, particularly loud noises
- Genetic predisposition (hereditary hearing loss)
- Head injury
- Structural malformation of the ear(s)
- Ototoxic drugs (drugs that are toxic to the ears)
Presbycusis is the most common cause of sensorineural hearing loss. It is caused by the natural aging process, occurs gradually, and initially affects the ability to hear high pitched sounds. Presbycusis is progressive, and is estimated to affect 30 to 40 percent of people over age 65. Noise-induced hearing loss can compound the effect of presbycusis. Hearing aids may be beneficial.
Sudden onset sensorineural hearing loss occurs either very suddenly or over the course of a few days. The type of hearing loss requires immediate medical attention by an otologist (doctor specializing in diseases of the ear). Any delay may decrease the chances of effective treatment.
Conductive hearing loss
The middle ear starts at your eardrum at the end of the ear canal. The eardrum moves with sound, and different pitches (high or low sounds) make the eardrum move less or more. The eardrum also makes the bones (ossicles) within it move, which sends a signal to the inner ear.
Conductive hearing loss occurs when sound cannot travel through the outer and middle ear, making soft sounds hard to hear and loud sounds seem muffled. It can affect one or both ears. Conductive hearing loss is usually not permanent and medicine or surgery can often repair it.
This type of hearing loss has many different causes, including:
- Otitis media (middle ear infection)
- Hole in the eardrum, such as a rupture
- Benign tumors
- Fluid in the middle ear from allergies, cold or flu viruses
- Earwax (cerumen) buildup
- A foreign object stuck in the outer ear
- Eustachian tube dysfunction
- Structural malformation of the ear(s)
Mixed hearing loss
This type is just what it sounds like – a mix of both sensorineural and conductive hearing loss. There may be damage in the outer or middle ear and the inner ear at the same time. Having both sensorineural and conductive hearing loss can make hearing loss worse than with only one of these types.
Causes include the same most common causes for both sensorineural and conductive hearing loss. An example of how this type of hearing loss occurs would be a ruptured eardrum from an ear infection and working around loud noises for a long time. Hearing aids may be beneficial for mixed hearing loss.
Auditory neuropathy spectrum disorder
Auditory neuropathy occurs when damage to the inner ear or the hearing nerve causes normal sound entering the ear to be organized in a way the brain cannot understand. The inner hear successfully detects sound, but cannot successfully transmit it to the brain.
This type of hearing disorder can affect people of any age. According to the National Institute on Deafness and Other Communication Disorders, it is unknown how many people this condition affects, but researchers believe “auditory neuropathies play a substantial role” in hearing loss.
Degrees of hearing loss
Regardless of type, hearing loss is categorized in degrees ranging from mild to profound.
- Mild hearing loss results in soft sounds being hard to hear, though most speech sounds can be heard.
- Moderate hearing loss may result in no speech being discernable when someone is talking at a normal sound level.
- Severe hearing loss is defined by no speech being heard at a normal level and only some loud noises.
- Someone experiencing profound hearing loss will be unable to hear any speech and only very loud sounds.
Other hearing loss definitions
Hearing loss has many other clinical descriptions used for further classification, such as the following:
- Unilateral: hearing loss in one ear
- Bilateral: hearing loss in both ears
- Pre-lingual: happened before a person learned to talk
- Post-lingual: happened after a person learned to talk
- Symmetrical: loss is same in both ears
- Asymmetrical: loss is different in each ear
- Progressive: occurs over time
- Sudden: happens quickly
- Fluctuating: gets better or worse over time
- Stable: stays the same over time
- Congenital: present at birth
- Acquired or delayed onset: appears later in life