The science of hearing loss

What actually happens to our ears when they’re subjected to noise: a complete guide to the mechanics of noise induced hearing loss.

First things first, what is noise-induced hearing loss?

Every day, we experience sound.  Some of these sounds, naturally, are above what’s considered the safe zone of hearing.  When our ears are exposed to noises above the safe zone, we sustain damage.  We’ve covered the extent to which people are unaware of just how easy damage can occur in this post, but suffice to say it’s very easy to unwittingly cause NIHL. 

Sounds above 85 decibels are generally considered unsafe, some quick examples include:

  • Heavy city traffic – 85 decibels
  • Motorbikes – 95 decibels
  • A maximum volume mp3 player – 105 decibels
  • Police sirens – 120 decibels

Both the length of time you’re exposed to the noise and your distance to the source of the sound will also have a heavy impact.

Exactly how does noise damage our hearing?

First, a brief step by step of exactly how our hearing works:

  1. Sound waves enter the outer ear and then travel through the ear canal, a narrow passage that leads to the eardrum.
  2. The eardrum vibrates from the sound wave, sending the vibrations to three tiny bones in the middle ear known as the malleus, the incus and the stapes.
  3. These three bones then couple sound vibrations from the air to fluid vibrations in the cochlea, a fluid filled, snail-shaped sac in the inner ear.
  4. When the vibrations cause the fluid inside the cochlea to ripple, a travelling wave then forms along the basilar membrane.  Hair cells ride the wave.
  5. As the hair cells move up and down, microscopic hair-like projections (called stereocilia) bump against an overlying structure and bend.  This bending causes pore-like channels at the tips of the stereocilia to open up.  Chemicals then rush into the cell, causing an electrical signal.
  6. The electrical signal is carried to the brain along the auditory nerve.

So what is hearing loss?

Put simply, NIHL results from irreparable damage to the stereocilia themselves.   Human hair cells simply don’t grow back (it’s for this reason that male pattern baldness is permanent, Wayne Rooney excepted).

As a result, the process is short circuited and the signal is unable to reach the auditory nerve.

Is this instant?

On some occasions, permanent hearing damage can arise almost instantly (such as when the ear is in the immediate vicinity of an exceptionally loud noise).  However, it’s more common for the damage to take place over a longer period and at a more gradual rate.

Can NIHL be prevented?

Yes.  As we’ve mentioned before, there are a number of ways in which you can help to prevent damage to your hearing:

  • Be aware of which noises are going to cause damage
  • Wherever possible, wear earplugs and other protective devices.
  • Move away from any noise sources you can’t protect yourself from
  • Have semi-regular hearing tests to ensure that you’re not sustaining damage.

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