According to the American Speech-Language-Hearing Association, there are three basic types of hearing loss:
Conductive Hearing Loss—hearing loss that occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and bones of the middle ear. This type of hearing loss can often be corrected medically or surgically.
Possible causes of conductive hearing loss include:
- Fluid in the middle ear
- Ear infections
- Perforated eardrum
- Impacted earwax
Sensorineural Hearing Loss—hearing loss that occurs when the inner ear is damaged. This is the most common type of permanent hearing loss, and usually cannot be corrected medically or surgically. Even when speech is loud enough to hear, it may still be unclear or sound muffled.
Some possible causes of sensorineural hearing loss:
- Certain illnesses
- Ototoxic medications
- Genetic or hereditary earing loss
- Head trauma
- Exposure to loud noise
Mixed Hearing Loss—hearing loss that occurs when both conductive and a sensorineural hearing loss take place together. This may indicate damage in the outer or middle ear and in the inner ear (cochlea) or auditory nerve.
Degrees of Hearing Loss
Degree of hearing loss refers to the severity of the loss. The table below shows one of the more commonly used classification systems. The numbers are representative of the patient’s hearing loss range in decibels (dB HL).
|Degree of hearing loss||Hearing loss range (dB HL)|
|Normal||–10 to 15|
|Slight||16 to 25|
|Mild||26 to 40|
|Moderate||41 to 55|
|Moderately severe||56 to 70|
|Severe||71 to 90|
|Source: Clark, J. G. (1981). Uses and abuses of hearing loss classification. Asha, 23, 493–500.|