Noise induced hearing loss (NIHL)

What is noise induced hearing loss?

We’re exposed to sounds from our surroundings every day - from television and music through to household appliances and passing traffic. Usually, these sounds are at safe levels, so don’t risk causing any damage to our hearing. But if they are too loud or persistent, they can be harmful, even if only temporarily. When sounds are both loud and long-lasting, this can have a detrimental effect on your hearing. 

Loud and persistent noises can damage sensitive structures in the inner ear, which can eventually lead to noise-induced hearing loss (NIHL). Because this is often a gradual process, it might take someone a while to realise that their hearing has been damaged. The louder the sound, the shorter the amount of time it takes for NIHL to happen.

How noise can damage our hearing

To understand how loud noises can damage our hearing, we have to understand how we hear. Hearing depends on a series of events that change sound waves in the air into electrical signals. Our auditory nerve then carries these signals to the brain through a complex series of steps:

1. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
2. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
3. The bones in the middle ear conduct the sound vibrations from the air to fluid vibrations in the cochlea of the inner ear, which is shaped like a snail and filled with fluid. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
4. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave.
5. As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open. When that happens, chemicals rush into the cell, creating an electrical signal.
6. The auditory nerve carries this electrical signal to the brain, which translates it into a sound that we recognise and understand.

Most NIHL is caused by the damage and eventual death of these hair cells. Unlike bird and amphibian hair cells, human hair cells don’t grow back - they are gone for good.

What causes noise induced hearing loss?

Sound is measured in units called decibels. Sounds at or below 70 A-weighted decibels (dBA), even after long exposure, are unlikely to cause hearing loss. However, long or repeated exposure to sounds at or above 85 dBA can cause hearing loss. The louder the sound, the shorter the amount of time it takes for NIHL to happen. Here are the average decibel ratings of some familiar sounds: 

• Normal conversation 
  60-70 dBA
• Cinema
  74-104 dBA
• Motorcycles and dirt bikes
  80-110 dBA
• Music through headphones at maximum volume, sporting events, and concerts
  94-110 dBA
• Sirens
  110-129 dBA
• Fireworks show
  140-160 dBA
  

How common is noise induced hearing loss?

The World Health Organization (WHO) estimates that approximately 360 million people worldwide suffer from severe hearing loss and approximately 1.1 billion young people (aged between 12 and 35 years old) face hearing loss as a result of noise.² According to Healthy Hearing our world has gotten so noisy that noise pollution is now considered a public health threat.³

What types of noise induced hearing loss are there?

Noise-induced hearing loss can be temporary or permanent and affect one or both ears.

Temporary noise-induced hearing loss

This occurs when a person is subjected to a sudden, extremely loud noise. Symptoms include muffled hearing, dizziness, and pain in the ear, for a short period of time. 

Long-term noise-induced hearing loss

This happens when a person has been exposed to continuous loud noises over a long period of time. Often long-term NIHL occurs in a noisy workplace environment. Some of the most common industries where employees report long-term NIHL are the military, manufacturing, transportation, and construction.

Recreational activities involving loud or continuous noise can also cause long-term NIHL, for example, target shooting, going to music concerts, or even regularly mowing the lawn.

What are the symptoms of noise induced hearing loss?

Symptoms can last for minutes, hours or days after noise exposure ends. Even if hearing returns to normal, cells in the inner ear could still be permanently damaged. If enough healthy cells are left, hearing will eventually come back, but hearing loss can become permanent if more cells get destroyed over time. 

As the damage from noise exposure is usually gradual, it can be easy to ignore the signs until they become more obvious. There are a few things to look out for when identifying the first signs of potential hearing loss. Some of the most common NIHL symptoms include:

• Inability to hear high-pitched sounds
• Muffled or distorted speech
• Tinnitus (ringing or buzzing in the ear)
• A feeling of fullness or pressure in the ear

How is noise induced hearing loss treated?

There is no cure for NIHL but In most cases hearing aids can be used to counter the hearing loss issues. If the hearing loss gets worse over time, hearing aids might not be sufficient and other options such as cochlear implants could be recommended. 

Can noise induced hearing loss be prevented?

Yes. It is one of the only types of hearing loss that is preventable. Good general advice is to avoid noises that are too loud, too close, or last too long. By becoming more aware of the hazards of noise and practicing good hearing health, you can protect your hearing by taking some simple steps:

• Be aware of the noises that can cause damage, so you know when you need to protect yourself
• Wear earplugs or other protective devices when participating in a loud activity (activity-specific earplugs and earmuffs are available at most hardware stores)
• Turn down the volume on sounds where possible, such as music and television
• If it is not possible to reduce the noise or protect your ears from it, try to move away from the source of the sound as much as possible
• Take breaks from long exposure of loud noises
• Be alert to hazardous noises in the environment and attempt to remove yourself from them
• Protect the ears of children who are too young to protect their own
• Help family, friends, and colleagues to become aware of the hazards of noise
• Have your hearing tested as soon as you feel any signs of potential hearing loss 

Help with hearing loss

For more information and tips on how to help prevent noise-induced hearing loss, visit It's a Noisy Planet. Protect Their Hearing^®. Amplivox is a member of the Hearing Conservation Association and is committed to improving the hearing health for people across the world. 

For occupational health practitioners who deal with adults who have experienced hearing loss issues, we offer several occupational health courses within audiometry. The courses all offer some learning and insight around NIHL.

For more information on any of our occupational health training courses please visit our occupational health courses webpage or contact our customer support team on +44 (0)1865 880 846, or email.

References

¹National Institute on Deafness and other Communication Disorders (Mar 2022) Noise-Induced Hearing Loss. Accessible at:
https://www.nidcd.nih.gov/health/noise-induced-hearing-loss

²S. Chadha, S. & A. Cieza (2017) Guest editorial: Promoting global action on hearing loss. World Hearing Day. Accessible at:
 http://dx.doi.org/10.1097/AUD.0000000000000413

³ J. Victory (2021) Noise-induced hearing loss (NIHL). Healthy Hearing. Accessible at:
 https://www.healthyhearing.com/help/hearing-loss/noise-induced-hearing-loss