About 1.1 billion people live with some hearing loss
Hearing loss ranges from partial weakness to total deafness, in one ear or both, from birth or later. Roughly half of global cases could be prevented by vaccines, safer pregnancy care, quieter sound, and cautious drug use—yet as of 2013 about 466 million people already lived with disabling loss.
A healthy ear spans roughly 20 to 20,000 hertz and is keenest around 3,000; zero decibels marks the faintest sound an average listener detects, not silence, and 115 dB is the pain threshold. Clinicians diagnose hearing loss when someone cannot hear 25 dB in at least one ear, then grade it from mild, 25 to 40 dB, up to profound, beyond 90 dB. Early signs include struggling with higher-pitched voices, losing speech in noisy rooms and turning the television up.
Causes stack genetics, ageing, noise, infections, birth complications, ear or brain injury and certain medicines. Cytomegalovirus, syphilis or rubella during pregnancy can damage a baby's hearing, which is why every newborn is meant to be screened. Age-related loss usually hits both ears as hair cells in the cochlea die off, and prevalence roughly doubles with each decade after 40. The World Health Organization advises young people to cap loud listening, including personal audio players, at about an hour a day.
Of the 466 million with disabling loss, about 124 million have moderate to severe disability, 108 million of them in low- and middle-income countries, and for 65 million it began in childhood. Hearing aids are often unaffordable; New Zealand subsidises them by age, severity and need, and some providers there now spread the cost into monthly subscriptions. Sign language, cochlear implants, subtitles and lip reading also help, though many in Deaf culture see deafness as a difference rather than a disability and regard implants warily.
Researchers consistently link hearing loss with cognitive decline and dementia, with risk climbing as loss deepens. Whether that includes Alzheimer's specifically is disputed across studies, and early data hinting that hearing aids slow the decline remain preliminary.
Source: Hearing loss
