The three main types of hearing loss describe the underlying cause of the hearing loss and include sensorineural hearing loss, conductive hearing loss and mixed hearing loss.
Sensorineural hearing loss
The most common type of hearing loss is known as sensorineural hearing loss. It is a permanent hearing loss that occurs when there is damage to either the tiny hair-like cells of the inner ear or the auditory nerve itself, which prevents or weakens the transfer of nerve signals to the brain. These blocked nerve signals carry information about the loudness and clarity of sounds.
If a child is born with sensorineural hearing loss, it is most likely due to a genetic syndrome or an infection passed from mother to fetus inside the womb, such as toxoplasmosis, rubella or herpes. When sensorineural hearing loss develops later in life, it can be caused by a wide variety of triggers, including:
- Deterioration caused by age (presbycusis)
- Blood vessel diseases
- Auto-immune diseases
- Infections such as meningitis, mumps, scarlet fever and measles
- Traumatic injuries
- Extremely loud noises or loud sounds that last for an extended periods of time
- Meniere's disease
- Acoustic neuroma or other cancerous growths in the inner ear
- A side effect through the use of certain medicines
- Noise exposure
The symptoms of sensorineural hearing loss affect both the loudness and the clarity of sounds:
- Noises may seem too loud or too quiet
- Difficulty following a conversation when two or more people are speaking at the same time
- Problems listening in noisy environments (e.g. train stations, construction sites, convention centers, sports arenas, etc.)
- Difficulty hearing women's or children's voices
- Certain speech sounds are difficult to hear during conversations (e.g. the "s" or "th" sound)
- Speech of others may seem slurred or mumbled
- A consistent ringing or buzzing in the ears
- A feeling of being off-balance or dizzy
There is no medical or surgical method of repairing the tiny hair-like cells of the inner ear or the auditory nerve if they are damaged. However, sensorineural hearing loss can be treated quite successfully with hearing aids or cochlear implants, depending on the severity of the loss. Assistive listening devices, like alerting devices, vibrating alarm clocks and captioned phones help provide a complete hearing solution.
Conductive hearing loss
A less common type of hearing loss is conductive hearing loss, which occurs when there is an obstruction or damage to the outer or middle ear that prevents sound from being conducted to the inner ear. Conductive hearing loss may be temporary or permanent, depending on the cause.
The causes of conductive hearing loss can be differentiated by which part of the ear they affect - either the outer or middle ear:
- Stenosis or a narrowing of the ear canal
- Wax impaction
- Exostoses (bone-like protrusions that can develop inside the ear canal and cause potential cause blockages)
- Otitis externa (also known as swimmer's ear)
- Obstructions caused by foreign bodies inserted into the ear
- A breach in the tympanic membrane caused by injury, ear infections or extreme and rapid air pressure changes
- Tympanosclerosis or a thickening of the tympanic membrane
- Otitis media or a buildup of fluid in the middle ear
- Blockages in the eustachian tube, which connects the middle ear to the back of the nose and throat
- Otosclerosis, a rare medical condition that causes the middle ear bones to freeze up
- Abnormal growths or tumors that form within the middle ear, such as cholesteatoma or glomus tumours
- Ossicular chain discontinuity, or a break in the connection between the bones of the middle ear, caused by injury or heavy trauma
Because the sensitive inner ear and auditory nerve are intact, an individual suffering from conductive hearing loss primarily has difficulty with the overall loudness of sounds, but not the clarity. Individuals with this kind of loss often find that turning up the volume of the radio or television is all it takes to improve their ability to hear. The following symptoms are also consistent with this type of loss:
- Easier time hearing out of one ear than the other
- Sensation of pain in one or both ears
- Sensation of pressure in one or both ears
- Difficulty or frustration with telephone conversations
- A peculiar smell emanating from the ear canal
- A feeling that one's own voice sounds louder or different
There are sometimes medical or surgical treatments that can improve hearing ability for those with conductive hearing loss. For example, conductive losses caused by wax impaction, foreign objects, abnormal growths or ear infections can often be corrected with medical treatments, like extraction of earwax, antibiotics or surgical procedures. These causes usually result in temporary hearing losses. The treating physician and hearing healthcare professional will monitor hearing ability and work with the patient to determine when and if a hearing solution is needed.
Mixed hearing loss
Mixed hearing loss is any combination of sensorineural and conductive hearing loss.
Mixed hearing loss commonly occurs when the ear sustains some sort of trauma. It can also happen gradually over time, when one hearing loss is compounded by another. For example, an individual with a long-standing conductive hearing loss might experience presbycusis as they age. Alternatively, an individual with sensorineural hearing loss may have a temporary mixed hearing loss due to wax impaction.
The symptoms of mixed hearing loss will be some combination of those listed above for the other two types of hearing loss.
Treatment options for mixed hearing loss will depend on whether the loss is more sensorineural or conductive in nature. If a greater portion of the loss is caused by a conductive component, surgical procedures and other medical treatments might be more effective in correcting the hearing concerns. If a greater portion of the loss is sensorineural, hearing aids or implantable devices may be the best option.
If you (or your loved ones) think you might have a hearing loss, it's important to consult with a physician and a hearing healthcare professional to investigate the cause and corresponding treatment options. Many conductive and mixed hearing losses can be remediated with medical intervention and all hearing loss is treatable with hearing aids, implantable devices and/or assistive listening devices.