Everyday sounds in our environment, such as those from our phones, televisions, radios, household appliances, and traffic, are normally at safe levels that don’t damage our hearing. But sounds can be harmful when they are too loud, even for a brief time, or when they are both loud and long-lasting. These sounds can damage sensitive structures in the inner ear and cause noise-induced hearing loss (NIHL).

What is Noise Induced Hearing Loss?

Hearing loss is a decrease in your ability to hear or understand speech and sounds around you. It can result from damage to hair cells, membranes, nerves or other parts of the inner ear that responds to sound and can happen when any part of the ear or the nerves that carry information on sounds to your brain do not work in the usual way. 

NIHL is usually caused by exposure to excessively loud sounds and cannot be medically or surgically corrected. It can result from a one-time exposure to a very loud sound, blast, or impulse, or from listening to loud sounds over an extended period. 

 

NIHL comes in many forms. It can be immediate or it can take a long time to be noticeable. It can be temporary or permanent, and it can affect one ear or both ears. Even if you can’t tell that you are damaging your hearing, you could have trouble hearing in the future, such as not being able to understand other people when they talk, especially on the phone or in a noisy room. 

A recent CDC study recorded at least 10 million adults (6 percent) in the U.S. under age 70—and perhaps as many as 40 million adults (24 percent)—have some degree of hearing loss in one or both ears from exposure to loud noise. Researchers have also estimated that as many as 17 percent of teens (ages 12 to 19) have varying levels of NIHL in one or both ears.

How can noise damage our hearing?

To understand how loud noises can damage our hearing, we have to understand how we hear. We hear sound because of vibrations, or sound waves, that reach our ears and are converted into electrical signals. We recognize those signals as speech, music, or other sounds. 

The outer ear—the part of the ear you see—funnels sound waves into the ear canal. The sound waves travel through the ear canal to reach the eardrum.

The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear, called the malleus, incus, and stapes. These bones amplify, or increase, the sound vibrations and send them to the inner ear.

The inner ear contains a snail-shaped structure filled with fluid called the cochlea. An elastic partition, called the basilar membrane, runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. 

Sound vibrations create waves in the cochlear fluids along the basilar membrane, which causes hair cells to move up and down. In turn, this causes tiny hair cells, called stereocilia, to bend, which causes chemicals that create electrical signals to come out of its tips. 

The auditory nerve carries this electrical signal to the brain in a complex series of steps, which translates it into a sound that we recognize and understand.

 

Source: NIH/NIDCD

 

Stereocilia perch atop sensory hair cells in the inner ear.

Source: Yoshiyuki Kawashima

Damage to hearing

Loud noise can damage cells and membranes in the cochlea and prolonged exposure can overwork hair cells in the ear, which can cause these cells to die. After leaving a very loud event, such as a concert or football game, you may notice that you don’t hear as well as before, might not hear whispers, sound might seem muffled, or you may hear ringing in your ears. 

Normal hearing typically returns after a few hours to a few days. Hair cells, like blades of grass, bend more if sound is louder, but will become straight again after a recovery period. However, loud noise or repeated exposure to loud noises can damage or kill some of the hair cells.

Hearing loss progresses as long as exposure continues, although some harmful effects might continue even after noise exposure has stopped. Damage to the inner ear or auditory neural system is generally permanent, since unlike bird and amphibian hair cells, human hair cells do not regenerate.

The average person is born with about 16,000 hair cells within their cochlea. These cells allow your brain to detect sounds. Sometimes up to half of these hair cells can be damaged or destroyed before changes in your hearing can be measured by a hearing test. By the time you notice hearing loss, many hair cells have been permanently destroyed.

In addition to damaging hair cells, noise can also damage the auditory nerve that carries information about sounds to your brain. Early damage may not show up on your hearing test. It can create a ‘hidden hearing loss’ that may make it difficult for you to understand speech in noisy places. 

Furthermore, extremely loud bursts of sound, such as gunshots or explosions, can also affect other parts of the ear structure, through the rupturing of the eardrum or damaging the bones in the middle ear causing immediate and permanent NIHL.

Causes

NIHL can be caused by a one-time exposure to an intense “impulse” sound, such as an explosion, or by continuous exposure to loud sounds over an extended period of time, such as noise generated in a woodworking shop.

Recreational activities that can put you at risk for NIHL include target shooting and hunting, snowmobile riding, listening to music at high volume through earbuds or headphones, playing in a band, and attending loud concerts. Harmful noises at home may come from sources including lawnmowers, leaf blowers, and woodworking tools.

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.

Your distance from the source of the sound and the length of time you are exposed to the sound are also important factors in how these sounds can damage your hearing.

Here are the average decibel ratings of some familiar sounds: 

• Normal conversation 60-70 dBA
• Movie theater 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

What are the effects and signs of NIHL?

When you are exposed to loud noise over a long period of time, you may slowly start to lose your hearing. Because the damage from noise exposure is usually gradual, you might not notice it, or you might ignore the signs of hearing loss until they become more pronounced. Sometimes exposure to loud noises causes a temporary hearing loss that disappears 16 to 48 hours later. 

Research suggests, however, that although the loss of hearing seems to disappear, there may be residual long-term damage to your hearing. Over time, sounds may become distorted or muffled, and you might find it difficult to understand other people when they talk or have to turn up the volume on the television. 

The damage from NIHL, combined with aging, can lead to hearing loss severe enough that you need hearing aids to magnify the sounds around you to help you hear, communicate, and participate more fully in daily activities.

Loud noise exposure can also cause tinnitus—a ringing, buzzing, or roaring in the ears or head. Tinnitus may subside over time, but can sometimes continue constantly or occasionally throughout a person’s life. 

Can NIHL be prevented?

NIHL is the only type of hearing loss that is completely preventable. If you understand the hazards of noise and how to practice good hearing health, you can protect your hearing for life. Here’s how:

• Know which noises can cause damage.
• Wear earplugs or other protective devices when involved in a loud activity (buy activity-specific earplugs or earmuffs).
• If you can’t reduce the noise or protect yourself from it, move away from it.
• Be alert to hazardous noises in the environment.
• Protect the ears of children who are too young to protect their own.
• Make family, friends, and colleagues aware of the hazards of noise.
• Recognize symptoms, causes, and effects of NIHL
• Have your hearing tested if you think you might have hearing loss.

Please take care of your hearing by following the above guidelines. To find a pair of protective hearing devices, read our next article here.