Causes of Hearing Loss

Causes of hearing loss in children and adults are divided into two broad categories: congenital and acquired.

Congenital causes are factors present at birth. This does not always mean that the child is born with a hearing loss. For example, genetic factors present at birth accound for about 50% of all hearing losses, but genetic hearing losses often appear later in life. Other congenital causes of hearing loss include a variety of diseases and infections during pregnancy, such as rubella (German measles), cytomegalovirus, herpes simplex, complications associated with Rh factor in the blood, maternal diabetes, or toxemia. Anoxia before, during, or immediately after birth can also result in hearing loss.

If a child has a congenital factor that could cause a hearing loss, it's a good idea to have an audiologist monitor the child's hearing, especially in the early years, as this allows parents and caregivers to take action immediately if the child begins to show signs of a hearing loss.

Acquired hearing losses are due to environmental factors occurring after the child is born. A variety of viral infections can cause damage to the middle or inner ear, or the auditory nerve, including meningitis, measles, mumps, encephalitis, chicken pox, influenza, and otitis media (ear infections). Head trauma and noise exposure can also be causes of hearing loss. Finally, there are a number of drugs that are known to be ototoxic, or toxic to the ears. These include some (but not all) chemotherapy drugs, some (but not all) antibiotics, and some (but not all) pain relievers.

A fluctuating or temporary hearing loss may occur as a result of recurring cases of otitis media. The middle ear fills with fluid, impeding the transfer of sound energy from the outer ear to the inner ear. When the infection heals, the fluid is reabsorbed, and hearing returns to normal. Similarly, some people produce unusually large amounts of ear wax and lose some of their hearing when the ear canal becomes blocked. When the wax is removed (not with Q-tips!!!), hearing returns to normal.

One of the biggest environmental causes of hearing loss (if not the biggest) is noise exposure. As our world grows more industrialized and more electronically connected, silent spaces are becoming increasingly rare. My extended family gathers every summer at a lakeside cabin in rural Michigan, where our ears are assaulted by boat and jet-ski traffic, our neighbors' stereos, fireworks (we usually go in early July), and airplanes flying overhead. My house in a "quiet" residential neighborhood sits on a bus route, a few blocks from the junction of two state highways, and under the landing pattern of the local airport. The farm where my father grew up now has the Pennsylvania Turnpike running through it.

Most of the noise pollution around us is not loud enough to cause a hearing loss, but as sources of noise become more numerous, we need to be mindful of what noise levels we and our children are being exposed to. For children, teens, and young adults, listening to loud music is a common cause of noise-induced hearing loss. The ubiquitous MP3 player has made music more portable and accessible than ever, and the use of earphones allows the listener to set the volume as loud as desired without drawing angry glares from those nearby. With the ability to listen to music louder, more often, and for longer periods of time comes increased opportunity for hearing loss.

How loud is too loud?

Generally speaking, the louder the noise, the more damage it can do. Some noises, such as a bomb exploding, can cause instant and permanent damage. More commonly, however, noise-induced hearing loss results from prolonged exposure to noise that is less extreme, though still loud. In general, if noise levels are below 75 dB (about the level of a washing machine or air conditioner, or a toilet flushing), there is no risk of hearing loss, no matter how long you are exposed.

Here are some examples of dangerously loud noises, and how long it takes them to cause permanent hearing loss:

  • 85 dB: 8 hours (Busy city traffic, vacuum cleaner, noisy office/restaurant, blender)
  • 90 dB: less than 2 hours (garbage disposal, tractor, shouted conversation)
  • 95 dB: less than 1 hour (hair dryer, electric drill, motorcycle)
  • 100 dB: 15 minutes (factory machinery, night club/disco)
  • 105 dB: less than 5 minutes (gas-powered lawn mower, peak volume of music on earphones with volume set at 5/10; )
  • 110 dB: less than 2 minutes (baby crying, squeaky baby toy held next to the ear, gas-powered leaf blower, symphony concert, car horn)
  • 115 dB: 30 seconds (leaf blower, rock concert, chain saw)

If a sound causes pain, it's around 125 dB. Recall that the decibel scale is logarithmic, so this is ten times as loud as 115, the level where hearing loss can occur in 30 seconds. You should act immediately to protect or remove yourself from noise at this level.

Many of the sounds I've listed are the sort that we encounter more in adulthood, but there are also noises that babies and young children are exposed to. As time goes by, more and more electronic toys and gadgets hit the shelves. If you buy toys that beep, honk, squeek, squawk, buzz, and whistle, you should be aware that there is no government regulation limiting the sound levels they emit. There is absolutely no guarantee that these products are safe for your children's hearing. You are on your own. My advice: if it's loud enough to be annoying, don't buy it. Even if it's not loud enough to cause hearing loss, it's still annoying, so why bother?

If you would like to learn more about the causes of hearing loss and how to prevent it, I recommend checking out the following sites:

National Institute on Deafness and Other Communication Disorders (NIDCD)

American Speech-Language and Hearing Association.

If you or someone you know has a hearing loss, it's a good idea to consult an audiologist on a regular basis to monitor changes in hearing and, if possible, to prevent further loss.

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