The cochlea hairs move so violently that they bend or snap off. A sudden loud noise like gunfire or an explosion can damage the cochlea. Long term exposure to loud noise is also a problem. Many people working in noisy environments like shipyards suffer damage to their hearing. In 1974 a law was passed limiting worker's exposure to noise and making the provision of ear protection compulsory.
Some drugs can damage the cochlea, especially streptomycin, or excessive use of aspirin.
A baby may be born deaf because of cochlea damage before birth as the result of infections during pregnancy. Mumps and meningitis can damage the cochlea. Meniere's disease also causes sensori-neural deafness. The effects of sensori-neural deafness High frequency hearing loss means you can hear people speaking, but can't always make sense of what they are saying. This is because you can't hear high frequency sounds, and most consonants are high frequency.