What is hearing loss?

Hearing loss¹ refers to the partial or loss of the ability to hear. Hearing loss can range from mild (hearing some speech sounds but having difficulty detecting soft sounds) to profound (being unable to hear soft sounds or speech, and only being able to detect very loud sounds).

Hearing loss can occur when any part of the ear is not working as it usually does. The structures affected by hearing loss can include the outer ear, middle ear, inner ear, acoustic (hearing) nerve, and the auditory system.

This condition can be caused by a number of environmental and physiological factors, including exposure to loud noise, congenital abnormalities, and simply losing the ability to hear as a result of aging.

There are multiple ways of describing hearing loss². Some of these include:

• Unilateral (affecting only one ear) or bilateral (affecting both ears)
• Pre-lingual or post-lingual (occurring before or after learning how to talk, respectively)
• Symmetrical or asymmetrical (or bilateral—having the same or different types of hearing loss in both ears)
• Fluctuating (worsening over time) or stable (remaining consistent)
• Congenital (present at birth) or acquired/delayed onset (appearing some time later in life)
• Progressive (worsening over time) or sudden (happening quickly)

How common is hearing loss?

Hearing loss is the third most common³ chronic physical conditions in the United States—it is more common than diabetes, vision trouble, and cancer. According to the NIDCD⁴ (National Institute on Deafness and Other Communication Disorders), about 2 to 3 of every 1,000 children in the United States are born with detectable hearing loss in one or both ears. Approximately 15% of American adults aged 18 and over report some trouble hearing, and 13% (1 in 8) people in the United States of age 12 or older have hearing loss in both ears, based on standard hearing examinations.

The strongest predictor of hearing loss among adults aged 20–69, however, is age—the greatest amount of hearing loss occurs in adults in their 60s. Men are almost twice more likely than women to have hearing loss (between ages 20–69), and Caucasian adults are more likely than adults in other racial/ethnic groups to have hearing loss.

Sensorineural hearing loss

One type of hearing loss⁵, sensorineural hearing loss, occurs when the inner ear (cochlea) or acoustic nerve is damaged or not working properly. This type of hearing loss causes sounds to be softer and more difficult to understand, especially when in a noisy environment.

Common causes of sensorineural hearing loss include:

• Congenital hearing loss (hearing loss is present at birth)
• Aging
• Exposure to loud noise
• Head injury
• Meniere’s disease⁶ (a disorder of the inner ear)
• Genetics
• Adverse reaction to medications

The symptoms of sensorineural hearing loss are sometimes treated with devices, hearing aids and cochlear implants.

Conductive hearing loss

Conductive hearing loss results from damage being done to the outer or middle ear, blocking sound from reaching the inner ear (cochlea). This type of hearing loss may cause the ears to feel plugged and make speech sound muffled, especially when there is a lot of background noise present.

Common causes of conductive hearing loss include:

• Malformations at birth, such as Microtia⁷ and Atresia⁸

• Down syndrome⁹, Goldenhar’s syndrome¹⁰, and Treacher Collins’ syndrome¹¹

• Chronic mastoiditis or otitis media¹² (middle ear infections)

• Middle ear skin growths or cysts (cholesteatomas¹³)

• Draining ears
• Chronic ear infections¹⁴

• Previous ear surgeries
• Benign (non-cancerous) tumors
• Genetics

There is a range of approaches used to treat conductive hearing loss, including medication, hearing aids, and surgery.

Mixed hearing loss refers to the presence of both conductive and sensorineural hearing loss.

Noise-induced hearing loss

Noise exposure¹⁵ is the second most common cause of hearing loss (behind aging). Approximately 40 million adults in the United States aged 20–69 have hearing damage in one or both of their ears. Once hearing has been damaged by loud noise, it cannot be fixed.

Primary healthcare providers can help determine whether hearing loss has been sustained and discuss the proper steps to take in diagnosing and treating the condition.

Hearing loss causes

It is important to understand how the ear works in order to understand how things like loud noise¹⁶ can cause hearing loss.

There are multiple structures in your ear that help you hear:

• The outer ear: The visible part of the ear that funnels sound waves into the ear canal. Sound waves travel through the ear canal to reach the eardrum.
• The middle ear: Here, sound waves vibrate the eardrum; these vibrations are sent to three tiny bones in the middle ear. These bones amplify the sound vibrations and send them to the inner ear.
• The inner ear: The inner ear contains a snail-shaped, fluid-filled structure called the cochlea. Sound vibrations create waves in the cochlear fluids. As these waves peak, they cause tiny hair cells (types of receptors that can detect sound) to bend, converting the vibrations into electrical signals.
• The auditory (hearing) nerve: This nerve carries the electrical signals from the inner ear to the brain, which then interprets these signals as a sound that you recognize and understand.

Noise can damage the hair cells, membranes, nerves, or other parts of the ear, causing temporary or permanent hearing loss.

Hearing loss can result from¹⁷ a single loud sound (like a firecracker) near your ear. However, hearing loss is most frequently caused by damage sustained over time from prolonged or repeated exposure to loud noise. Generally, the louder a sound is—and the longer the exposure to the noise—the greater the risk for hearing loss and the shorter the amount of time it takes for hearing loss to occur. The cumulative effect of noise determines how well you might hear later in life and how quickly you might develop hearing problems, even after exposure has stopped.

Damage to the inner ear or the auditory neural system is generally permanent.

Damaged hair cells in the ears

Loud noise is particularly harmful to the inner ear. A one-time exposure to extremely loud noise or listening to loud sounds for a long period of time can cause hearing loss by damaging the cells and membranes of the cochlea. Other structures in the inner ear are also susceptible to damage—listening to loud noise for a long time can overwork the hair cells in the ear, which can cause them to die. This hearing loss progresses as the exposure continues, and harmful effects from the loud noise may continue even after exposure to it has stopped.

After a very loud event, like a concert, you may notice that your hearing is not as sharp as it was before—you may hear ringing, feel that your ears are muffled, or not be able to hear soft sounds like whispers. Generally, however, normal hearing will return within a few hours to a few days. This is because your hair cells, like blades of grass, will eventually become straight again after being bent by strong sound waves.

If too many hair cells are damaged, however, some of them will die. Repeated exposure to loud noise will eventually destroy a large number of these cells, potentially leading to significant hearing loss.

The average person is born with about 16,000 tiny hair cells in their cochlea¹⁸. Around 30–50% of these hair cells can be damaged or destroyed even before any changes in your hearing are measurable by a hearing test. In other words, by the time you notice hearing loss, many of these hair cells may have been destroyed.

These cannot be repaired once damaged.

Ear nerve damage

In addition to damaging the hair cells in the inner ear, loud noise can also damage the auditory nerve that carries information about the sounds you hear to your brain for interpretation. Early nerve damage may not show up on a hearing test but can create a “hidden hearing loss” that may make it difficult for you to understand speech or soft sounds in noisy environments.

Ototoxic chemicals

According to the CDC, certain chemicals have been identified as ototoxic¹⁹—this means that they may cause hearing loss or balance problems, regardless of noise exposure. The substances containing ototoxic chemicals include certain pesticides, solvents, and pharmaceuticals. Ototoxicity can negatively affect how the ear functions and cause hearing loss and/or affect balance (the fluid in the cochlea found in the inner ear helps regulate balance).

The risk of experiencing adverse effects as a result of exposure to ototoxic substances increases when exposed to them around elevated noise levels. The combination of these two factors often results in hearing loss that can be either temporary or permanent (depending on the level of noise, the dose of the chemical[s], and the duration of the exposure). This hearing impairment can affect a variety of occupations and industries, from machinists to firefighters.

Occupational hearing loss

Occupational, or worker hearing loss²⁰, refers specifically to noise-induced hearing loss brought about by repeated exposure to loud noise as a result of one’s workplace environment. In the United States, hearing loss is among the most common work-related illnesses—over 11% of the working population has hearing difficulty, reports the CDC, and nearly 1 out of 4 cases of worker hearing difficulty is caused by work-related exposures.

The occupational risks for exposure to hearing damage include both loud noise and ototoxic chemicals. There are workers in every industry sector that are exposed to noise or chemicals that can damage hearing, or both. Noise is considered to be potentially harmful when it reaches 85 decibels or higher, or if the surrounding environment is so loud that a person has to raise his or her voice to speak to someone 3 feet away (at an arm’s length).

In the U.S. workplace:

• Approximately 22 million workers (17%) are exposed to hazardous noise each year.
• About 10 million workers are exposed to solvents that can damage hearing.
• An unknown number of workers are exposed to other ototoxic chemicals that can damage hearing.

Among all workers exposed to loud noise, 19% have hearing impairment (hearing loss impacts day-to-day activities, such as being able to understand speech).

Non-occupational noise-induced hearing loss

As its name suggests, non-occupational noise-induced hearing loss²¹ refers to hearing loss not caused by work-related noise or chemical exposure. Common home and community activities can cause hearing damage, such as using gas-powered lawnmowers or attending a loud concert.

The CDC found that of the 40 million U.S. adults aged 20–69 with noise-induced hearing damage in one or both ears, more than half (53%) reported no exposure to loud noise at work. Based on this information, researchers believe that this hearing damage comes from exposure to loud sounds during everyday activities in homes and communities.

Although loud noise is all around us, much of noise-induced hearing loss is preventable. Some steps you can take to prevent hearing loss caused by day-to-day exposure include:

• Avoiding noisy places, when possible
• Stepping away from the sound source and minimizing the amount of time spent in noisy environments
• Using earplugs, protective earmuffs, or noise-canceling headphones
• Keeping the volume down at home or in the car, and take breaks from listening to music through earbuds or headphones
• Going to your provider for a checkup if you have been exposed to loud noise or are concerned that you aren’t hearing as well as once did

Hearing loss in children

According to the CDC, over 98% of newborns²² in the United States were screened for hearing loss in 2016. There are a variety of causes for newborns having congenital (present at birth) hearing loss. These causes appear to often be related to genetic factors—genes were responsible for hearing loss among 50–60% of children with the condition.

Of those newborns screened:

• About 20% of babies with hearing loss had a “syndrome” (such as Down syndrome or Usher syndrome)
• Infections in the mother during pregnancy, complications after birth, and other environmental causes were responsible for hearing loss among almost 30% of babies with hearing loss
• The most common developmental disability to co-occur with hearing loss was intellectual disability (23%), followed by cerebral palsy (10%), autism spectrum disorder (7%), and/or visual impairment (5%), according to ongoing tracking in metro Atlanta²³

Risks for noise-induced hearing loss

The following factors can increase your risk²⁴ for developing noise-induced hearing loss:

• Genetics and individual susceptibility to noise
• Long-standing (chronic) conditions, such as diabetes and high blood pressure (hypertension)
• Injuries to the ear
• Organic liquid chemicals, such a toluene

Certain medications have been shown to be ototoxic²⁵. The damage that these medications may cause to the ear can result in hearing loss, ringing in the ears (tinnitus), or a loss of balance. More than 200 medications have been identified as ototoxic²⁶, including antibiotics, cancer treatment drugs, pain relievers containing salicylate, and many other medicines.

Furthermore, certain industries may pose a risk for hearing health—namely, those that involve prolonged exposure to loud noise, such as mining and construction.

Hearing loss symptoms

Some signs²⁷ and symptoms of hearing loss²⁸ include:

• Muffling of speech and other sounds
• Difficulty understanding speech or sounds, especially against background noise or in a crowd
• Difficulty understanding speech over the phone
• Frequently asking others to repeat what they’ve said or speak more loudly, slowly, and clearly
• Frequently needing to turn up the volume on the television or radio
• Difficulty distinguishing between consonant sounds (for example, having trouble differentiating between “s” and “f” or “th” and “sh” sounds in conversation)
• Ringing in the ears
• Hypersensitivity to (being bothered or caused pain by) certain sounds
• Difficulty hearing high-pitched sounds (like birds, the doorbell, the telephone, or an alarm clock)
• Ringing in the ears
• Withdrawal from conversations or avoidance of some social settings

Talk to your healthcare provider if you experience one or more of these symptoms, especially if difficulty hearing is interfering with your daily life. As age-related hearing loss occurs gradually, you might not notice it at first.