To understand hearing loss requires a basic understanding of how we hear.

Your outer ear acts like a dish that collects sound waves.  These sound waves travel along the ear canal and vibrate against the eardrum.  In the middle ear, three tiny bones (the smallest bones in the human body) transfer the vibrations to the fluid-filled cochlea in the inner ear.  This creates ripples in the fluid, which bend the hair cells in the cochlea.  This movement is converted into electrical impulses that are carried through the auditory nerve to the brain where they are translated into meaningful sounds.

As you can see, hearing is a complex process.  As with any such process, a lot of things can go wrong.  Here are the most common types of hearing loss and their causes:

Sensorineural loss indicates that the nerve endings in the inner ear are not transmitting sound properly.  Sound waves can reach the middle ear without difficulty, but there is some type of damage to the inner ear, usually the hair cells or nerve fibers.  If the hair cells or nerve fibers are not working correctly, the inner ear loses its ability to transmit the necessary signals to the brain for sound recognition. Sensorineural hearing loss can be caused by disease; certain medications, such as some powerful antibiotics; exposure to loud noise; lightning injury; head injury; natural loss over time as one ages or from inherited genes. Most adults with hearing problems have sensorineural hearing loss.  Hearing aids are often used as a means of rehabilitation for this condition.

Presbycusis is a type of hearing loss that comes with aging or heredity.  The hair cells in the cochlea change with age or an inherited gene can cause this change.  This means that sound information is no longer sent properly to the brain for processing.  Presbycusis is one type of sensorineural hearing loss.

Noise-induced hearing loss is usually caused by years of exposure to loud sounds although sudden noise trauma, such as from an explosion, can also cause it.  Noise-induced hearing loss is another type of sensorineural hearing loss.

Conductive loss means sound is not being sent properly to the inner ear.  Conductive hearing loss is usually caused by a disease or disorder that affects how sound waves travel through the outer or middle ear.  Because of this, the sound waves have difficulty reaching the eardrum, and the hearing process is interrupted.  This is usually treated with medication or surgery.

Mixed hearing loss is a combination of conductive and sensorineural hearing impairment.