The Mechanism

Sound is transmitted through the ear to the cochlea, where tiny hair cells convert vibration into nerve signals. Excessive noise destroys those hair cells, and in humans they do not regenerate. The loss is permanent.

How it presents

• Damage starts around 4 kHz, a frequency range that carries little of everyday conversation, so early loss goes unnoticed.
• Consonants — s, t, f, th — are lost before vowels, so speech becomes audible but unclear. The classic complaint is "people mumble".
• Background noise becomes disproportionately disabling: a conversation in a quiet room is fine, the same conversation in a canteen is impossible.
• Tinnitus — permanent ringing — often accompanies it, and is frequently the more distressing symptom.
• By the time the person notices, a large proportion of hair cells are already gone.

Temporary threshold shift

The dullness and ringing after a noisy shift is a temporary threshold shift. It recovers overnight — but it is a warning that damage is occurring, and repeated shifts produce permanent loss. Treat it as an exposure alarm, not a normal end to the day.