Noise-induced hearing loss is on the rise among the young. Some 65 percent of those with hearing problems are below retirement age. Audiologists believe that part of the problem is the number of gadgets that send amplified sound directly into the ear canal, such as cell phones and MP3 players.

Loud Noises Damage Cilia

Sound is created when noise beats against the eardrum and the vibrations stimulate nerves deep inside the ear. There, fine hair cells called cilia convert the vibrations into nerve impulses, which are transmitted to the brain.

Continued exposure to noise of 85 decibels or more will eventually destroy the fragile hair cells in the inner ear that convert sound vibrations into nerve impulses -- the basis of hearing. The volume of portable compact disc players ranges between 91 and 121 decibels, and earphones increase the volume. European iPods have a legal upper limit of 100 decibels, but there is no such limit in the United States.

Damage Happens Quickly

The louder the noise, the quicker the hearing loss. For instance, 100-decibel stereo headphones can cause harm in two hours, and a 120-decibel rock concert damages the ears in only 7.5 minutes. The musicians' advocacy group Hearing Education and Awareness for Rockers (HEAR) reports that 86 percent of musicians and music fans experience hearing problems after a concert.