Causes Of Hearing Loss

The human ear is a delicate instrument, and its anatomy is just as delicate. To understand how most people lose their hearing, we first must look at how the whole process of hearing works.

One of the things that’s most remarkable about our hearing is that it’s not chemical in nature, but is mechanical. In that, it is completely different from most of our body’s processes such as digestion or the sense of smell, which are chemical processes. In order for you to be able to hear, the ear must pick up the sound waves—which actually are very tiny pressure waves in the air—that are generated by any kind of noise. Then it must convert those sound waves into electrical impulses that your brain can understand.

organ of corti

Without getting into the entire anatomy of the ear—which is both amazing and complex—let’s look at one tiny part called the Organ of Corti. The Organ of Corti is essentially the “microphone” where sound waves are received and processed.

Inside the Organ of Corti are thousands of tiny hair cells. Again, without getting into all the mechanics of what happens, when the ear receives a sound wave, the hair cells move in response to differences in pressure, which sends an electrical impulse to nerves inside the ear and let those nerves know that there’s something going on.

Those hair cells are crucial to the process of hearing. If they don’t work, or if they’re damaged, then the ear can’t make sense of the incoming pressure waves.

ORGAN OF CORTI
Imaged licensed under the Creative Commons Attribution-ShareAlike 3.0

Damage to the hair cells—through noise exposure or disease—is the most common cause of hearing loss.

Now, consider this: when you’re born, you have approximately 29,000 hair cells in your ears. They’re divided into two categories in each ear, with about 3500 inner hair cells and 11,000 outer hair cells in each Organ of Corti.

By the time you’ve reached the age of 20, your hearing already has started to diminish slightly. This is easy to demonstrate—kids love high pitched ring tones for their cell phones that they can hear but their parents can’t.

This type of hearing loss also is a normal process of aging. By the time you’re 65, you will have lost about 40% of those hair cells, and this does affect your hearing.

So now that we know that, we can look at how people’s hearing can be damaged.

One of the most common causes of hearing loss is through noise exposure. In fact, 80% of hearing loss occurs this way. Noise exposure—whether from listening to loud music over a long period of time or standing too close to an explosion—can damage those sensitive hair cells and prevent them from working properly.

The process is painless, and—except in the case of noise trauma such as gunfire or an explosion—very gradual, so you don’t even realize it’s happening. This is why it’s so important to protect your ears from noise exposure whenever you can.

Although noise exposure is the most common cause of hearing loss, it’s not the only one. Some families have genetic factors that either result in hearing loss or predispose people to hearing loss. Unfortunately, there really isn’t much you can do about these factors but protect your hearing from other types of damage.

Otosclerosis is a disease that affects the movement of some very tiny bones in the middle ear. Although it can cause hearing loss it often can be treated with surgery.

A number of medications can damage your hearing. These medications include high doses of aspirin, several strong antibiotics, and a number of chemotherapy drugs. Sometimes you need to weigh the possible benefit from the medication involved against the potential hearing damage and decide which is more important.

Physical head injuries can cause hearing damage. Hearing damage may result from a torn or punctured ear drum or from damage to the structure of the ear itself.

Older people may suffer from presbycusis, which is a gradual hearing loss that takes place as you age. In this kind of hearing loss, the first thing you lose is the higher tones (the higher pitched notes) so you have trouble understanding what people—especially women—are saying to you.

Meniere’s Disease and an associated condition, hydrops, cause pressure increases within the inner ear. Although the cause of these conditions is a mystery, there is some very preliminary evidence from studies in Europe that a herpes infection of the inner ear may be involved. Meniere’s Disease causes vertigo, tinnitus (ringing in the ears), hyperacusis (sensitivity to loud noises) and hearing loss; hydrops has the same symptoms except for the vertigo. The amount of hearing loss from these conditions varies, and depends in part on how well the doctor and patient are able to manage the disease. The hearing loss results in part from damage to the hair cells caused by the increased pressure in the inner ear.

One type of sudden hearing loss is auto-immune inner ear disease. With this type of hearing loss, the patient just wakes up one morning deaf or nearly so. If the patient can get straight to an emergency room and insist on treatment by a hearing specialist quickly, the hearing loss from this condition can be minimized.

A tumor known as an acoustic neuroma also can cause hearing loss. The patient has one ear that feels “full,” and experiences tinnitus and hearing loss. This condition also can be treated.

Repeated middle ear infections are the most common cause of hearing loss in children. A middle ear infection is called otitis media. The main symptom is inflammation behind the eardrum; usually there’s a buildup of fluid as well. Otitis media can be mild or severe.