Why is noise damage to human hearing permanent?

Our ears can be harmed by sound that is very loud, even for a short time, or by sound that is loud and goes on for a long time. The damage is called noise-induced hearing loss, and it can affect one ear or both.

Loudness is measured in decibels. Sounds at or below 70 decibels are unlikely to harm hearing, even if you hear them for a long time. Repeated exposure to sounds of 85 decibels or more can cause damage, and the louder the sound, the faster the damage happens. A motorcycle can reach 80 to 110 decibels, a concert 94 to 110, a siren 110 to 129, and fireworks 140 to 160. How close you are to the noise, and how long you hear it, both matter.

The damage happens deep inside the ear, to tiny hair cells that respond to sound. In birds and frogs these cells can grow back. In humans they cannot: once they are destroyed, they are gone for good. Because the loss is often gradual, people may not notice it until it has become serious. Loud noise can also cause tinnitus, a ringing or buzzing in the ears.

There is good news, though. Noise-induced hearing loss is the only kind of hearing loss that can be completely prevented, by avoiding very loud sounds, keeping a distance from them and wearing ear protection.