Stop the Decibel Damage
If your ears were ringing during the Fourth of July fireworks, you experienced firsthand the daggerlike effect of intense sound waves on your inner ear. No surprise. Firecrackers explode with decibels so great that a sudden dose of more than a few minutes in duration could make one permanently stone-cold deaf. This is no old wives' tale, though most of the time noise-induced loss of hearing creeps up painlessly and silently. All too many middle-agers are just finding that out as they line up for their hearing aids in search of relief from those strained conversations in crowded rooms, where everyone around them seems to be mumbling. Waiting to join them in line are the growing ranks of younger people. A Harvard survey of adolescents and young adults reported that more than half had taken a hit to their hearing at loud music events, either tinnitus or temporary deafness. And from my observation, most seem to have iPods attached to their ears. For them, and the others who can still hear a pin drop, it's smart to pay attention to the health of the inner ear, the nerve center for making sense of sound.
Loud noise destroys nerve endings in the inner ear and is a common and preventable cause of hearing loss. Decibels measure loudness: Silence is zero and the explosion of a firecracker, 150 dB. A rock concert can get up to 140; a noisy bar, almost 100. As a general rule, a whisper is 30 dB; the purr of a quiet motor is 40, and a normal conversation, 60. Regular exposures to levels over 85 are toxic to the ear.
The blast of a jet engine or an Indy racing car and an explosion or gunshot are obvious culprits. But it's the power tools and lawn mowers, the blare of music through earphones, the hair dryers and vacuum cleaners and noisy places that cause damage gradually over time. And you don't need a decibel meter to know what's too loud: If you have to raise your voice to be heard above the din, you are in a toxic place.
Deafening sounds are like blinding light, pointedly destroying the very organ that detects them. This irony is testimony to an evolved life, in which the human ear has just not kept up with modern times. That is, the hairlike, specialized nerve endings that are lined up inside a coiled, fluid-filled compartment of the inner ear can be shaken to death by loudness they were not designed to handle. These nerve endings vibrate at different rates in response to different sound frequencies, more slowly for the low pitch of a baritone and faster for the higher pitch of a soprano, transforming them into distinct electrical impulses sent through the auditory nerve to the brain.
Just as you can blow out an electrical circuit by overloading it, these vibrating hair cells can be overexcited by too much noise. When forced into metabolic overdrive, the cells spin off toxic oxidation products that make them swell and sometimes slowly die off. Toxic noise also compromises blood flow to the inner ear, causing further damage. The cells that go first are those that resonate to a higher pitch, and the resulting dropout of higher-frequency sounds is what makes words seem garbled.
Preventive measures. Recognition that these nerve endings were designed for a quieter time, when men hunted with bows and arrows and women washed their clothes in babbling brooks, has inspired preventive efforts that were not even considered a few years back. Neurobiologist Josef Miller from the Kresge Hearing Research Institute at the University of Michigan stresses noise avoidance and when a loud sound environment is unavoidable, earplugs or muffs, which can cut noise by 30 dB or more. These measures have been incorporated into most occupational safety programs and inspired such innovations as quieter hair dryers and volume-limited iPods. Just recently, Apple filed a patent for new software designed to track a headphone user's exposure to loud music and automatically reduce volume as needed. On the horizon is a nutrient bar to fight off ear damage, says Miller. He and others have shown that a combination of the antioxidant vitamins A, C, and E and magnesium not only protects the inner ear when taken before noise exposure but can limit damage for up to 72 hours after the insult. As Miller points out, this approach would add to current ear-protection devices or help those who can't or won't wear earplugs or muffs.
Don't I know. I pleaded with my girls to use earplugs during last week's festivities. But the rocking music on the Mall and the loud display of fireworks just drowned me out. I will keep trying.
This story appears in the July 16, 2007 print edition of U.S. News & World Report.