Hearing loss can be categorized by which part of the auditory system is damaged. There are three basic types of hearing loss: conductive hearing loss, sensorineural hearing loss, and mixed hearing loss.
Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear. Conductive hearing loss usually involves a reduction in sound level or the ability to hear faint sounds. This type of hearing loss can often be corrected medically or surgically.
Some possible causes of conductive hearing loss:
- Fluid in the middle ear
- Ear infection (otitis media)
- Perforated eardrum
- Benign tumors
- Impacted earwax (cerumen)
- Infection in the ear canal (external otitis or swimmer’s ear)
- Presence of a foreign body
- Absence or malformation of the outer ear, ear canal, or middle ear
Sensorineural hearing loss occurs when there is damage to the inner ear (cochlea), or to the nerve pathways from the inner ear to the brain. Most of the time, sensorineural hearing loss cannot be medically or surgically corrected. This is the most common type of permanent hearing loss.
SNHL reduces the ability to hear faint sounds. Even when speech is made loud enough to hear, it may still be perceived as unclear or muffled.
Some possible causes of SNHL:
- Drugs that are toxic to hearing
- Hearing loss that runs in the family (genetic or hereditary)
- Head trauma
- Malformation of the inner ear
- Exposure to loud noise without the use of hearing protection
Sometimes a conductive hearing loss occurs in combination with a sensorineural hearing loss. In other words, there may be damage in the outer or middle ear and in the inner ear or auditory nerve. When this occurs, the hearing loss is referred to as a mixed hearing loss.