Hearing Loss Types & Hearing Loss Causes

How Hearing Works

The ear has three main parts or sections - the outer ear, middle ear and inner ear. Each section has a specific function that allows sound waves that enter the ear to be transformed into electrical impulses that the brain can understand. The outer ear collects sound waves and directs them to the middle ear. The middle ear then amplifies the sound and transmits it to the inner ear. The inner ear converts the sound vibrations into electrical impulses that travel along the auditory nerve to the brain.

The outer ear catches sound waves and directs them into the ear canal.
The ear canal carries the sound waves to the eardrum (tympanic membrane).
Sound waves cause the eardrum (tympanic membrane) to vibrate.
The bones in the middle ear (malleus, incus and stapes) pick up these vibrations.
Vibrations pass through the oval window to the cochlea, setting the fluid inside in motion. This causes special nerve cells to turn the sound waves into electrical impulses.
The auditory nerve sends these electrical impulses to the brain where they are heard as sound.

Types of Hearing Loss

When any part of the hearing system is unable to function, the result is hearing loss. There are several types of hearing loss:

Conductive hearing loss is caused by damage to the outer or middle ear. With a conductive loss, sound waves are blocked as they move through the outer or middle ear. Since the sound cannot be conducted efficiently, the sound energy that reaches the inner ear is weaker or softer. A conductive loss can result from infection, excessive earwax buildup, fluid in the middle ear, damage to the middle ear bones, a perforation of the eardrum or a foreign body in the ear canal.

Signs/symptoms may include:

Perceiving speech and other sounds as faint or muffled
Ear pain or discharge from the ear
Redness or swelling of the outer ear
Pressure or fullness in the ear

Sensorineural hearing loss is caused by damage to the inner ear. Sound waves travel normally through the outer and middle ear, however, the inner ear is unable to pick up the vibrations or is unable to send the vibrations to the brain. Also called "nerve deafness", it usually occurs in both ears. A sensorineural loss can result from infection, disease, certain drugs, excessive noise, birth defects and aging.

Signs/symptoms may include:

Perceiving speech and other sounds as distorted or unclear
Difficulty hearing certain pitches (usually high pitches)
Hearing a ringing or buzzing sound that is constant or periodic
Difficulty understanding speech in the presence of background noise

Mixed hearing loss is caused by damage to the outer/middle ear and the inner ear. Typically, sound waves are not conducted efficiently to the inner ear, and once they reach the inner ear the vibrations cannot be picked up or sent to the brain. Therefore, a mixed hearing loss is the combination of a conductive and sensorineural hearing loss.

Signs/symptoms may include:

See "Signs/Symptoms" under Conductive hearing loss & Sensorineural hearing loss.

Central hearing loss is caused by damage to the auditory nerve or hearing centers. Sound waves are transmitted normally through all three parts of the ear, however, the auditory nerve may not be able to send the electrical impluses to the brain or the hearing centers of the brain may not receive the signals correctly. A Central loss can result from head injuries, disease or tumors.

Signs/symptoms may include:

Detecting sound but not being able to understand or process it