Your inner ear has 15,000 tiny hairs and are very delicate. When sound reaches these hairs they physically respond by moving.
Now think of these hair cells as a field of lush green grass.
When you walk on the grass it bends the grass down beneath your feet.
The grass springs back upright once you’ve walked by, and the hair cells in your ear do the same thing, they bounce back after receiving a sound. With safe sounds (those under 85 decibels), the hair cells have no problem springing back up.
But not all sounds are safe. Prolonged exposure to sounds at 85dB or greater begins to do damage.
Imagine walking around on that lush green field of grass for eight hours: the grass will still be alive and mostly intact, but it’s going to be bent and worn, and some small patches may be crushed completely.
So it is with the hairs in your inner ears: long exposure to loud noise wears out those hair cells, and some of them become irreparably worn out, damaged, and unable to contribute to translating sound vibrations into signals your brain can interpret.
That’s noise-induced hearing loss in a nutshell.