A Little Bit Louder, Please

But progress is being made on many fronts. Awareness and prevention efforts--community-based, state and nationwide programs--are gaining support around the country as hearing loss is increasingly recognized as a public-health issue. Advances in digital technology have dramatically improved hearing aids; they are smaller than ever, with far better sound quality. And clinical trials are now underway on permanent, implantable hearing aids for the middle ear which will offer sound that is superior even to the best external aids. On the biological front, scientists are busy trying to unlock the genetics of hearing to find a way to regenerate the sensitive hair cells, essential for hearing, that line the cochlea, the spiral, seashell-like structure located in the inner ear. And way out on the horizon of the cutting edge, researchers have created an experimental brain-implant system that bypasses the ear altogether and sends sound from an external receiver to the part of the brainstem that processes sound (page 49).

The product of extraordinary, even beautiful, anatomy, hearing is a natural wonder and exactly the sort of gift we tend to take for granted. "Unfortunately, a lot of people do not value their hearing," says Dr. William Slattery, director of clinical studies at the House Ear Institute in Los Angeles. Hearing may also be too good for its own good. Human ears were originally meant to pick up the faintest sounds of predators stalking our long-ago ancestors--the snap of twigs in the forest, the rustle of grass on the savanna. The crash and racket of modern life, both urban (motorcycles, subway trains, car alarms) and rural (chain saws, snowmobiles, shotguns), assault and insult these gorgeous instruments.

Most common types of hearing loss occur at the higher frequencies and are caused by damage to hair cells. Slattery describes the cochlea as "a piano, with 15,000 keys rather than 88." Different parts of the cochlea process different frequencies of sound, so when you have hearing loss at a certain frequency, it's as if that part of the keyboard is not functioning. Various levels of noise affect hair cells in various ways. If a rocket-propelled grenade goes off right next to you, you can experience "acoustic trauma" that kills hair cells and causes the instant loss of a great deal of hearing. (Hearing loss is the third most commonly diagnosed service-related ailment, according to the Department of Veterans Affairs.) Hanging out directly in front of the speakers at a Green Day concert could result in a less serious "temporary threshold shift," in which the hair cells are stressed but not permanently damaged. Such stress is often accompanied by ringing in the ears that can last for hours or even days. (Derebery notes that repeated threshold shifts can lead to permanent hearing loss.) And then there's what might be called noisy-world syndrome. While an individual's noise exposure may not reach the official danger zone, the worry is that the chronic din of daily life could lead to deterioration over time. "There's not a lot of data about it," says Rabinowitz, "but our concern is that there is less and less time for the ears to rest, and so the hair cells are going to be prematurely exhausted."

Protecting your hearing starts with understanding how noise works. The classic "formula" for assessing the risk of hearing loss is the intensity of the noise, measured in decibels (the danger starts at 85 decibels, roughly the sound of a lawn mower), multiplied by duration, the time of exposure. In other words, the louder the noise, the less time you should be exposed to it. Prolonged exposure to any noise above 85 decibels can cause gradual hearing loss. According to what experts call the "five-decibel rule," for each five-decibel increase, the permissible exposure time is cut in half. So one hour at 110 decibels is equivalent to eight hours at 95 decibels. And sound levels above 116 decibels (snowmobiles are about 120, rock concerts about 140) are unsafe for any period of time.

For millions of Americans, excessive noise in the workplace is a daily threat. Angelo Iasillo, 45, has worked in road construction since 1989, operating jackhammers and a "road grinder" to tear up Chicago's streets. He first noticed a problem with his hearing when he was in his early 30s and found himself asking more and more people to repeat themselves. He also demonstrated another classic symptom. "I was always putting the TV up louder," he recalls. Worried, he went to the doctor and was told, at 32, that he had the hearing of an 80-year-old. Today, Iasillo wears a hearing aid, uses a vibrating alarm clock that he keeps under his pillow and has his doorbell rigged to a lamp--it blinks when someone rings.

While the Occupational Safety and Health Administration (OSHA) has made great headway against noise-induced hearing loss in the past 20 years, compliance with federal regulations can be a problem in some occupations. Earplugs would certainly help protect road workers like Iasillo, but to be safe at busy work sites they also need to hear what is happening around them. And some professions are louder than we think. Truckdrivers, for example, have a high incidence of hearing loss in their left ears from traffic noise, says Hinrich Staecker, professor of otolaryngology at the University of Maryland School of Medicine.