How hearing works

Sound travels as vibrations through the air. Those vibrations enter your outer ear, travel down the ear canal, and strike the eardrum. The eardrum vibrates, moving three tiny bones in the middle ear — the malleus, incus, and stapes — which amplify the sound and transmit it to the fluid-filled cochlea in the inner ear.

Inside the cochlea, thousands of tiny hair cells convert those fluid vibrations into electrical signals. The auditory nerve carries those signals to the brain, which interprets them as sound. Damage or disruption anywhere along this pathway can cause hearing loss.

What counts as hearing loss?

Hearing loss is measured in decibels (dB) of hearing level. A person with normal hearing can detect sounds as quiet as 0–25 dB. Hearing loss is classified by how loud a sound needs to be before you can hear it:

• Mild (26–40 dB): Difficulty hearing soft speech, especially in noisy environments.
• Moderate (41–55 dB): Difficulty following normal conversation without amplification.
• Moderately severe (56–70 dB): Loud speech is hard to understand without hearing aids.
• Severe (71–90 dB): Only very loud sounds are audible without amplification.
• Profound (91+ dB): Little to no usable hearing without powerful amplification or cochlear implants.

The three main types of hearing loss

Hearing loss is categorized by where in the auditory system the problem occurs:

Sensorineural hearing loss

The most common type, accounting for about 90% of all hearing loss in adults. It results from damage to the hair cells in the cochlea or to the auditory nerve itself. This type is usually permanent but treatable with hearing aids or, in severe cases, cochlear implants.

Conductive hearing loss

Caused by a problem in the outer or middle ear that prevents sound from being conducted efficiently to the inner ear. Common causes include earwax buildup, fluid in the middle ear, ear infections, or a perforated eardrum. This type is often temporary and medically treatable.

Mixed hearing loss

A combination of both sensorineural and conductive hearing loss — meaning there is damage in both the inner ear and the outer or middle ear. Treatment addresses both components.

Common causes of hearing loss

• Aging (presbycusis): The most common cause. Gradual deterioration of hair cells over decades.
• Noise exposure: Prolonged or sudden loud noise damages hair cells permanently.
• Genetics: Hereditary factors account for more than 50% of congenital hearing loss.
• Ear infections: Repeated infections can damage the middle ear structures.
• Ototoxic medications: Certain antibiotics, chemotherapy drugs, and high-dose aspirin can damage hearing.
• Head trauma: Injury to the head or ear can disrupt the auditory pathway.
• Disease: Conditions like Meniere's disease, meningitis, and otosclerosis can cause hearing loss.

Is hearing loss reversible?

It depends on the type and cause. Conductive hearing loss caused by earwax, fluid, or infection is often fully reversible with medical treatment. Sensorineural hearing loss — the most common type — is generally permanent, because damaged hair cells in the cochlea do not regenerate. However, hearing aids and cochlear implants can restore functional hearing for most people.

Sudden sensorineural hearing loss (sudden deafness) is a medical emergency. If treated with corticosteroids within 72 hours, some or all hearing may be recovered. This is why sudden hearing loss should never be ignored.

How common is hearing loss?

Hearing loss is the third most common chronic physical condition in the United States, after high blood pressure and arthritis. According to the National Institute on Deafness and Other Communication Disorders (NIDCD):

• About 48 million Americans have some degree of hearing loss.
• 1 in 3 adults over age 65 has hearing loss.
• Half of adults over 75 have disabling hearing loss.
• On average, people wait 10 years after noticing hearing loss before seeking help.

What to do if you think you have hearing loss

The first step is a hearing evaluation by a licensed audiologist or hearing instrument specialist. A comprehensive hearing test (audiogram) takes about 30–60 minutes and painlessly measures your hearing across a range of frequencies and volumes. From there, you and your provider can discuss whether hearing aids, medical treatment, or monitoring is the right path.

Don't wait. Research consistently shows that untreated hearing loss is associated with cognitive decline, depression, social isolation, and reduced quality of life. The sooner you address it, the better the outcomes.