Up to 28 million Americans have impaired hearing and for as many as a third, acoustic trauma is a significant contributor, reports the December 2007 issue of Harvard Men's Health Watch. On-the-job noise exposure is the most common cause, but recreational noise - such as loud music - is catching up, the report says.

Most often, noise-induced hearing loss begins with a subtle difficulty hearing high-frequency tones, then slowly begins to encompass lower tones. Usually, both ears are equally involved. Once your hearing is lost, it can't be restored; your only recourse is to wear a hearing aid.

If your ears ring or buzz after being exposed to noise, it's loud enough to cause damage. And if noise exposure makes hearing painful, muffled, blurry, or distant for hours or days, you are already in trouble, the report says.