Hearing Preservation

The system’s first line: catch trouble before it costs hearing. Sensitive tests now reveal damage long before it shows on a standard hearing test, and AI makes that detection cheap and scalable enough to reach everyone. The earlier a risk is seen — a noisy job, an early synapse loss, a difficulty hearing in noise — the more of the later protection actually works. This is the planning layer that targets every other defense, and the foundation of lifelong hearing resilience.

AI-assisted and smartphone audiometry, speech-in-noise testing, and early markers of cochlear damage (otoacoustic emissions and synapse measures) — detecting loss before it becomes permanent and matching protection to each person.

Hearing screening that fits in a phone. De Wet Swanepoel’s team at the University of Pretoria built validated smartphone-based hearing tests (hearScreen and the WHO’s hearWHO) that bring accurate screening out of the clinic and to whole populations — turning early detection into something everyone can reach.

Hearing trouble the standard test misses. Mead Killion developed the QuickSIN speech-in-noise test, showing that difficulty understanding speech in noise reveals real hearing damage even when a basic audiogram looks normal — catching functional loss early enough to protect.

Detecting damage before symptoms. Charles Liberman and Sharon Kujawa at Harvard Medical School and Mass Eye and Ear showed that the earliest noise damage — lost synapses — can be detected with sensitive electrophysiology before any permanent threshold shift, defining the window in which loss can still be prevented.



Sounds the ear emits, read as an early warning. Building on David Kemp’s 1978 discovery at University College London that the healthy cochlea emits its own sounds (otoacoustic emissions), Brenda Lonsbury-Martin and Glen Martin showed that distortion-product otoacoustic emissions detect noise-induced cochlear damage earlier and more sensitively than a standard pure-tone audiogram — flagging injury before it becomes permanent.

A reflex test that reveals hidden nerve damage. Michael Valero, Stéphane Maison, and Charles Liberman at Harvard Medical School and Mass Eye and Ear showed that the middle-ear-muscle reflex weakens in cochlear regions that have lost auditory-nerve synapses — making this simple, noninvasive measure a promising clinical marker for detecting hidden hearing loss in people.

Reading the nerve’s response to find loss the audiogram misses. Christopher Plack and colleagues at the University of Manchester developed electrophysiological and behavioral tests (auditory brainstem response wave-I amplitude and temporal-coding measures) aimed at diagnosing cochlear synaptopathy in humans with normal audiograms — working toward a practical test for the earliest, most preventable damage.Research & institutions: De Wet Swanepoel at the University of Pretoria, Mead Killion and the QuickSIN developers, Charles Liberman and Sharon Kujawa at Harvard Medical School and Mass Eye and Ear, the World Health Organization’s Make Listening Safe program, the National Institute on Deafness and Other Communication Disorders (NIDCD), the Centers for Disease Control and Prevention, the Department of Defense Hearing Center of Excellence, the University of Iowa audiology programs, the Eaton-Peabody Laboratories, Boys Town National Research Hospital, the American Academy of Audiology, and the broader audiology and early-detection field.

Noise is the largest preventable cause of hearing loss — and the ear has its own defenses against it. A built-in reflex turns down the cochlea’s sensitivity to loud sound, and the inner ear can even be “toughened” by its own stress response. This capability combines those natural protections with proven avoidance — limiting dose, distance, and duration — so the cochlea is shielded before damage occurs. It is the grounded foundation of hearing preservation, working entirely through the body’s own biology and simple, harm-free behavior.

The medial olivocochlear efferent reflex that protects the cochlea from loud sound, the cochlea’s own “sound-conditioning” stress response, and proven noise-dose reduction — the ear’s and the listener’s own protections against acoustic injury.

The ear’s own reflex that guards against loud sound. Charles Liberman and John Guinan at Harvard Medical School and MIT mapped the medial olivocochlear reflex — a feedback loop that turns down the cochlea’s amplification in noise — and showed it protects the inner ear from acoustic injury, a built-in shield the body already runs.

The cochlea can toughen itself. Donald Henderson and colleagues at the University at Buffalo showed that prior, moderate sound exposure makes the cochlea more resistant to later damaging noise — “sound conditioning,” the ear’s own stress-protective response that can be harnessed rather than overwhelmed.

Prevention works at population scale. The National Institute for Occupational Safety and Health (NIOSH) showed that hearing-conservation programs — reducing noise dose through engineering, distance, and protection — measurably cut occupational hearing loss, the grounded proof that prevention preserves hearing.



The middle-ear muscle that braces against loud sound. Erik Borg and S. Allen Counter characterized the human acoustic (stapedius) reflex — a fast, involuntary middle-ear muscle contraction that stiffens the ossicular chain and attenuates intense sound before it reaches the cochlea, the ear’s own built-in shock absorber against acoustic injury.

The brain’s feedback loop that limits noise damage. Stéphane Maison, Hidé Usubuchi, and Charles Liberman at Harvard Medical School and Mass Eye and Ear showed that the medial olivocochlear efferent system minimizes cochlear nerve damage from moderate noise — mice with the reflex disabled lost far more auditory-nerve synapses, proving this natural feedback actively protects hearing.

Strengthening the natural reflex prevents hidden hearing loss. Ana Belén Elgoyhen’s group at INGEBI-CONICET in Buenos Aires, working with Harvard collaborators, showed that genetically enhancing the medial olivocochlear feedback system made mice resistant to noise-induced cochlear synaptopathy — demonstrating that boosting the ear’s own protective reflex can prevent hidden hearing loss.Research & institutions: Charles Liberman and John Guinan at Harvard Medical School and the Massachusetts Institute of Technology, Donald Henderson at the University at Buffalo, the National Institute for Occupational Safety and Health (NIOSH), the World Health Organization’s Make Listening Safe program, the National Institute on Deafness and Other Communication Disorders (NIDCD), the Department of Defense Hearing Center of Excellence, the National Hearing Conservation Association, the House Institute, the Oregon Hearing Research Center, Brenda Lonsbury-Martin and Glen Martin’s otoacoustic-emissions research, and the broader noise-prevention and cochlear-physiology field.

Whether the threat is noise, aging, or toxic exposure, much of the damage to hearing runs through one common pathway: oxidative stress, a flood of free radicals that kills the inner ear’s sensory cells. But the cochlea has its own defenses — antioxidant systems and protective stress proteins. This capability is about strengthening those built-in defenses so the inner ear can better withstand the stresses of a lifetime, working from the cochlea’s own protective biology rather than adding anything foreign.

The oxidative-stress pathway shared by noise and ototoxic damage, the cochlea’s endogenous antioxidant defenses (glutathione), and protective heat-shock proteins — the inner ear’s own resilience, which can be supported and strengthened.

The damage runs through free radicals. Jochen Schacht’s lab at the University of Michigan showed that both noise and ototoxic exposure kill hair cells through oxidative stress, and that the cochlea’s own antioxidant defenses — built around glutathione — protect against that damage, identifying the pathway protection can strengthen.

The inner ear’s own emergency stress proteins. Lisa Cunningham’s lab at the National Institute on Deafness and Other Communication Disorders showed that heat-shock proteins, made by the ear’s own cells under stress, protect hair cells from dying after damage — a built-in defense that can be harnessed.

The cochlea’s own antioxidant reserves. Su-Hua Sha and Jochen Schacht (at the Medical University of South Carolina and the University of Michigan) showed that the inner ear’s own glutathione-based antioxidant reserves fall with age and noise — and that strengthening these endogenous defenses protects hair cells, an internal route to greater resilience that adds nothing foreign.



Replenishing the ear’s own antioxidant enzyme. Jonathan Kil and Sound Pharmaceuticals developed ebselen (SPI-1005), a drug that mimics glutathione peroxidase — the cochlea’s own protective enzyme, which drops after loud noise. In a randomized, placebo-controlled phase 2 trial led at the University of Florida, ebselen significantly reduced temporary noise-induced hearing loss.

Feeding the cochlea’s antioxidant defenses with vitamins and magnesium. Colleen Le Prell at the University of Michigan and University of Florida showed that a combination of vitamins A, C, and E plus magnesium (ACEMg) bolsters the inner ear’s free-radical scavenging and promotes sensory hair-cell survival, reducing permanent noise-induced hearing loss in animal studies.

A drug that boosts the inner ear’s own sulfur antioxidant. Kathleen Campbell at Southern Illinois University School of Medicine developed D-methionine, which raises the cochlea’s endogenous antioxidant reserves; in a Department of Defense-funded phase 3 trial, oral D-methionine was tested in soldiers to reduce noise-induced hearing loss during weapons training.Research & institutions: Jochen Schacht at the University of Michigan, Lisa Cunningham at the National Institute on Deafness and Other Communication Disorders, Peter Steyger at Creighton University, the Kresge Hearing Research Institute, the Oregon Hearing Research Center, the Hearing Health Foundation, the Department of Defense Hearing Center of Excellence, the University of Rochester, Su-Hua Sha at the Medical University of South Carolina, Henry Ou at the University of Washington, the broader otoprotection research community, and the broader cochlear oxidative-defense field.

A pivotal discovery in hearing preservation is that the first thing lost is not the hair cell — it is the synapse connecting that cell to the nerve. This “hidden hearing loss” happens early, often from noise, and explains why people struggle to hear in noise long before a standard test shows damage. This capability is about protecting and, where possible, regrowing those synapses using the ear’s own growth factors — catching the very first, most preventable stage of loss. Shared with auditory-nerve regeneration.

Cochlear synaptopathy (“hidden hearing loss”), the early and selective loss of hair-cell-to-nerve ribbon synapses, and neurotrophin-driven synapse preservation and regrowth — demonstrated in animals, with detection emerging in people.

Synapse loss comes first. Sharon Kujawa and Charles Liberman at Harvard Medical School and Mass Eye and Ear discovered that noise destroys the synapses between hair cells and nerve fibers before the hair cells themselves die — a hidden, early, and preventable injury they named cochlear synaptopathy (Kujawa & Liberman, Journal of Neuroscience, 2009).

The ear’s own growth factor regrows the synapse. Gabriel Corfas’s lab at the University of Michigan showed that neurotrophin-3 (NT-3) — a signal the inner ear naturally makes — regenerates lost cochlear synapses and recovers hearing in noise-exposed mice, restoring the connection from within (Wan et al., eLife, 2014).

Why it matters for real hearing. Stéphane Maison and the Eaton-Peabody Laboratories at Harvard linked this hidden synapse loss to the everyday difficulty of understanding speech in noise — making its protection a direct route to preserving usable hearing.



The ear’s own supporting cells supply the synapse’s growth signal. Gabriel Corfas and colleagues at the University of Michigan showed that cochlear supporting cells are the natural source of neurotrophin-3, and that boosting this internal supply drives ribbon-synapse regeneration and recovery of cochlear function after acoustic trauma — the ear repairing its own first point of loss.

A mid-life boost that prevents age-related synapse loss. Guoqiang Wan, Sharon Kujawa, Charles Liberman, and Gabriel Corfas showed that overexpressing neurotrophin-3 in the cochlea at middle age prevented the age-related loss of inner-hair-cell synapses and slowed age-related hearing loss in mice — protecting the connection before it is lost.

Mapping the molecules that keep the synapse working. Tobias Moser’s InnerEarLab at the University Medical Center Göttingen defined how the hair-cell ribbon synapse encodes sound with submillisecond precision and identified otoferlin as essential to its function — the detailed biology that shows exactly what must be protected to preserve hearing in noise.Research & institutions: Sharon Kujawa and Charles Liberman at Harvard Medical School and Mass Eye and Ear, Gabriel Corfas at the University of Michigan, Stéphane Maison and the Eaton-Peabody Laboratories, the Massachusetts Eye and Ear hearing-research program, the National Institute on Deafness and Other Communication Disorders, the Hearing Health Foundation, the Department of Defense Hearing Center of Excellence, the University of Rochester, Tobias Moser at the University of Göttingen, Albert Edge at Mass Eye and Ear, and the broader cochlear-synaptopathy field.

Much age-related hearing loss is not worn-out hair cells but a failing power supply. A tissue called the stria vascularis acts as the cochlea’s battery, generating the electrical charge that makes hearing possible, and it depends on a delicate blood supply. As it declines with age, hearing fades — a process called metabolic presbycusis. This capability is about protecting that metabolic engine and its blood supply, keeping the cochlea powered across decades, and it is a central thread of lifelong hearing resilience.

The stria vascularis and the endocochlear potential it generates, cochlear blood flow, and the metabolic and vascular decline behind age-related hearing loss — the cochlea’s power system, which protection aims to preserve.

Age-related hearing loss is often metabolic. Richard Schmiedt at the Medical University of South Carolina showed that a major form of presbycusis comes from decline of the stria vascularis and a falling endocochlear potential — the cochlea’s “battery” running down — rather than primary hair-cell loss, redefining what aging hearing protection must target.

Hearing depends on cochlear blood flow. Alfred Nuttall at the Oregon Hearing Research Center mapped how the cochlea’s tiny blood supply sustains its function and how disrupting it harms hearing — showing that protecting cochlear circulation protects hearing.

Mapping the aging cochlea. Kevin Ohlemiller at Washington University in St. Louis detailed how oxidative and vascular changes drive strial and cochlear aging — defining the targets for keeping the cochlea’s engine running longer.



The cochlea’s battery ages through inflammation. Hainan Lang and Judy Dubno at the Medical University of South Carolina showed, in both mouse and human cochleas, that the stria vascularis is one of the earliest sites of age-related decline — with dysfunctional, over-activated macrophages and an “inflammaging” signature degrading the strial cells that power hearing (Lang et al., Journal of Neuroscience, 2023).

Gap junctions recycle the potassium that drives hearing. Daniel Jagger and Andrew Forge at University College London mapped the connexin gap-junction networks of the cochlear lateral wall, showing they recycle potassium back to the endolymph and help generate the endocochlear potential — the metabolic circuit whose preservation keeps the cochlea charged.

Strial marginal cells run the cochlear power supply. Bradley Schulte and colleagues at the Medical University of South Carolina showed that the stria vascularis’ marginal cells, rich in Na,K-ATPase ion pumps, generate the endocochlear potential, and that the age-related fall in this potential tracks the decline of those ion-transport pumps — defining the cellular target for protecting the aging cochlea’s engine.Research & institutions: Richard Schmiedt at the Medical University of South Carolina, Alfred Nuttall at the Oregon Hearing Research Center, Kevin Ohlemiller at Washington University in St. Louis, the Kresge Hearing Research Institute, the National Institute on Deafness and Other Communication Disorders, the Hearing Health Foundation, the University of Washington, the broader presbycusis and cochlear-physiology community, Hainan Lang at the Medical University of South Carolina, the House Ear Institute, the Department of Defense Hearing Center of Excellence, and the broader aging-cochlea field.

Protecting hearing begins at birth. Universal newborn hearing screening now catches loss in the first weeks of life, when early support transforms a child’s language and development; and the leading preventable cause of childhood hearing loss — a common congenital infection — can be detected and managed early. This capability is about catching and preventing hearing loss from the very start, protecting the developing auditory system when it matters most — one of preventive medicine’s clearest, most grounded successes.

Universal newborn hearing screening via otoacoustic emissions, early detection and management of congenital cytomegalovirus (the leading non-genetic cause of childhood hearing loss), and protection of the developing auditory pathway.

Catching hearing loss in the first weeks of life. Christine Yoshinaga-Itano at the University of Colorado proved that infants whose hearing loss is identified and supported early — the “1-3-6” benchmark — develop dramatically better language than those identified late, the evidence that built universal newborn hearing screening.

The technology that makes infant screening possible. David Kemp at University College London discovered otoacoustic emissions — faint sounds a healthy cochlea produces — giving a quick, noninvasive way to test a newborn’s hearing and to detect cochlear damage before it is otherwise visible.

Preventing the leading infectious cause. Gail Demmler-Harrison at Baylor College of Medicine showed that congenital cytomegalovirus (CMV) is a leading preventable cause of childhood hearing loss, and that early detection allows hearing to be monitored and protected from the start.



Six months of antiviral treatment protects infant hearing. David Kimberlin at the University of Alabama at Birmingham led the NIH Collaborative Antiviral Study Group trial showing that six months of oral valganciclovir for babies with symptomatic congenital CMV improved hearing and developmental outcomes over six weeks of treatment (Kimberlin et al., New England Journal of Medicine, 2015).

Screening at birth, hearing aids by six months. Karl White, founder of the National Center for Hearing Assessment and Management at Utah State University, drove the implementation of universal newborn hearing screening across U.S. hospitals — turning a research idea into routine care that now reaches the great majority of American newborns.

Early cochlear implantation transforms spoken language. Ann Geers and colleagues, working with the CDaCI (Childhood Development after Cochlear Implantation) study team across U.S. centers, showed that deaf children who receive cochlear implants early develop markedly stronger spoken-language skills than those implanted later — evidence that protecting and intervening on infant hearing in the first months shapes lifelong language.Research & institutions: Christine Yoshinaga-Itano at the University of Colorado, David Kemp at University College London, Gail Demmler-Harrison at Baylor College of Medicine, the CDC’s Early Hearing Detection and Intervention (EHDI) program, the National Institute on Deafness and Other Communication Disorders, the American Academy of Pediatrics, the World Health Organization, Karl White and the National Center for Hearing Assessment and Management at Utah State University, the Joint Committee on Infant Hearing, Boys Town National Research Hospital, and the broader newborn-hearing and congenital-CMV field.

The inner ear’s sensory hair cells are surrounded and sustained by supporting cells — the cochlea’s own structural and caretaker cells that nourish the hair cells, maintain the precise environment they need, and hold the inner ear’s latent capacity to repair itself. In other animals, these are the very cells that regenerate lost hearing. This capability protects that population so the cochlea keeps both its working hair cells and its regenerative reserve — preserving, from the ear’s own biology, the foundation that hair-cell regeneration later builds on.

Cochlear supporting cells (Deiters’, pillar, and phalangeal cells), their maintenance of the hair-cell environment, and their latent progenitor capacity — the ear’s own caretaker and repair-reserve cells, whose preservation keeps the cochlea able to function and, potentially, to regenerate.

The ear’s own repair cells, identified. Andrew Groves at Baylor College of Medicine and Neil Segil at the University of Southern California showed that cochlear supporting cells retain a latent ability to become new hair cells — held in check in mammals — identifying the resident cells whose preservation keeps the inner ear’s regenerative reserve alive.

Supporting cells can rebuild lost hair cells. Albert Edge at Mass Eye and Ear and Harvard Medical School showed that cochlear supporting cells can be coaxed to replace lost hair cells — proof that keeping these cells healthy preserves the ear’s own route back to hearing, and the reason protecting them matters before loss becomes complete.

Caretaker cells keep the cochlea working. Jian Zuo and the broader cochlear-biology community showed that supporting cells sustain the structural and ionic environment hair cells depend on — so protecting them protects the function of the hair cells they surround, an endogenous foundation of lasting hearing.



Supporting cells are the inner ear’s resident progenitors. Huawei Li and Renjie Chai at Fudan University showed that Lgr5-positive cochlear supporting cells act as inner-ear progenitor cells — capable of proliferating and regenerating hair cells in the neonatal mouse cochlea both in culture and in the living ear — identifying the caretaker cells whose preservation keeps the regenerative reserve alive.

Notch signaling is the brake on the ear’s repair cells. Albert Edge at Mass Eye and Ear and Harvard Medical School showed that blocking Notch signaling with a gamma-secretase inhibitor releases cochlear supporting cells to transdifferentiate into new hair cells, partially restoring hearing in deafened mice — proof that the supporting-cell reserve carries usable regenerative capacity (Mizutari et al., Neuron, 2013).

Increased Notch keeps the repair reserve switched off. Patricia White at the University of Rochester showed that rising Notch activity in supporting cells is what prevents spontaneous hair-cell regeneration in the maturing mouse cochlea — identifying the molecular switch that silences the ear’s own repair cells, so that protecting them preserves the option to one day reawaken them.Research & institutions: Andrew Groves at Baylor College of Medicine, Neil Segil at the University of Southern California, Albert Edge at Mass Eye and Ear and Harvard Medical School, Jian Zuo at Creighton University, Stefan Heller at Stanford University, Ksenia Gnedeva at the University of Southern California, the Hearing Restoration Project of the Hearing Health Foundation, John Brigande at the Oregon Hearing Research Center, the National Institute on Deafness and Other Communication Disorders, the Department of Defense Hearing Center of Excellence, and the broader cochlear supporting-cell and inner-ear-regeneration field.