In the absence of loud noises, hearing doesn't appear to deteriorate much with age. Loud noises cause sensorineural hearing loss, which is the destruction of the tiny hair cells in the inner ear that signal the auditory nerve to send sound messages to the brain. Once those cells die, they never grow back. It affects both volume and clarity beginning at first with the inability to hear high pitches, then later speech or lower pitches. Tinnitus or a ringing in the ears is constant annoyance and often is a warning sign of future hearing loss.
Hearing aids can aid in both sensorineural hearing loss and tinnitus.
The louder the noise, the shorter the time it takes to hurt your hearing. Your ears can be subjected to 90 decibels of noise for about eight hours before damage occurs. For every 5 decibels above that, it takes only half as much time for damage to begin. Most people don't notice they've lost any hearing until they develop tinnitus or they can't understand speech. This Temporary Threshold Shift goes away, but it's a signal that you've damaged some hair cells in your inner ear.