Hearing Loss and You
The big thing to guard against is repeated and prolonged exposure to loud noises. Your ears and tympanic membranes make no distinction between a lawn mower and Wilco, so this includes amplified music, headphone listening, club going, and chain sawing—or even listening to Mozart, if you do so at 110dB.
When you listen to loud music for any length of time, you may become aware of a "ringing" in your ears This is not necessarily particularly bell-like—it may be a buzz, hiss, chirp, or whooshing noise. The technical name for this is tinnitus (ti-NITE-is or TIN-it-us) and it's a warning you should heed or you're in danger of hearing it for the rest of your life.
Exposure to loud noises is the most common, and most easily preventable, cause of tinnitus, but it is hardly the only one. Tinnitus can be caused by wax build-up within the ear (although don't necessarily rush out to have your ears cleaned; some cases have reportedly been caused by wax removal). Cardiovascular disease, certain medications, ear and sinus infections, head and neck traumas, and even misalignments of the jaw have also reportedly caused tinnitus.
However, the vast majority of cases that have been definitively attributed to a single cause are due to excessive noise. Sound is measured in decibels, a logarithmic scale, and the precise amount of exposure is a combination of loudness and duration, so it's not easy to give a precise point at which damage begins to occur, but a good rule of thumb is that if you have to shout in order to be heard, you're already there.
A one-time exposure to loud noises is unlikely to cause hearing damage, but repeated exposure almost certainly will—a point to ponder as more and more of us plug into our iPods to cancel out the noise pollution of an increasingly loud environment.
There is some promising news on the horizon, however. The January 13 issue of Science reports that researchers supported by the National Institute on Deafness and Other Communication Disorders (NIDCD) caused hair cells to regrow by blocking the action of a single gene in mice.
No, not hair cells that go outside the head, but rather the hair cells found in the cochlear, the part of the inner ear that sends the electrical signal of sound to the brain. When the eardrum vibrates, the bones of the middle ear relay those vibrations to the cochlear, where they stimulate the hair cells. This is the mechanical to electrical energy conversion that generates the signals carried by nerves to the brain, which then interprets them as sound.
In the Science study, the researchers isolated a gene that was activated in the ear of the mice. According to the American Tinnitus Association's website, "The gene, Rb1, encodes for the retinoblastoma protein, which has various functions throughout the body, including acting as a molecular switch to stop the growth of hair cells. Mice that were bred to be missing the retinoblastoma gene were found to have more hair cells than control mice. Mature hair cells grown in culture dishes also were able to regenerate when the retinoblastoma gene was blocked."
Of course, this is just the first step towards a viable treatment for hearing loss, but it is a giant one. In the meantime, keep it down—or wear hearing protection. Good (and relatively unobtrusive) prophylactics are available from Etymotic and Sensaphonics, among others.