Like an earplug in a pill

TED AX knows he should wear earplugs when he leans into the noisy engine compartment of an MG sports car. He's been working among clanging metal and whirring power tools in garages for the last 15 years and has already developed tinnitus, a ringing in the ears that is one of the most common symptoms of hearing loss caused by excessive noise.

But between the need to pinpoint troubled engine sounds and listen out for the phone -- and with his fingers forever covered in grease -- the Denver man's earplugs go unused.

"I have yet to come up with a real-world scenario where I can have hearing protection and do my job," says the 42-year-old foreign-car mechanic.

Ax might soon have a more amenable option -- a pill he could take before work that would help protect his ears from noise.

Ax is one of an estimated 30 million Americans who are exposed to hazardous levels of noise daily at work or at leisure, be it from the buzz of leaf-blowers and landscape equipment, the jangling of construction tools, the cacophony of a concert or the roar of a motorcycle engine. Until now, hearing protection for such people has consisted of using barrier devices such as earplugs or earmuffs and limiting the time a worker spends exposed to loud noises.

Recently, however, several groups have started testing various chemicals for their safety and effectiveness at preventing noise-induced hearing loss in people. If the tests go well and the drugs are approved by the Food and Drug Administration, they would be the first of their kind.

Noise damages hearing by stressing out the inner-ear cells that convert sound waves into electrical signals that travel to the brain. These hair cells vibrate in response to sound and can be both physically and chemically destroyed by noise.

Most commonly, noise causes levels of toxic chemicals called free radicals inside the hair cell to rise beyond manageable levels, and the cell dies. Once a hair cell dies, the body cannot replace it.

Damage can occur from repeated exposure to noise at or above 85 decibels -- the loudness of a busy city street or a vacuum cleaner -- or from a short burst of a very intense noise such as gunfire.

If too many hair cells die, the inner ear can no longer detect sounds from certain frequencies -- particularly, high-pitched sounds. Eventually, that hearing loss obscures conversation, dropping out sounds such as "ess" and "ch."