No right-thinking parent would let a child wear sunglasses if there was a chance they would damage his or her eyes. Yet millions of parents allow their kids to wear itty bitty headphones despite growing evidence that they can harm children's hearing.

No right-thinking parent would let a child wear sunglasses if there was a chance they would damage his or her eyes. Yet millions of parents allow their kids to wear itty bitty headphones despite growing evidence that they can harm children's hearing.

For years, experts have known that consistent exposure to loud sound, including amplified music, erodes hearing. Kids are pumping decibels directly into their ears with the headphones that are standard equipment for MP-3 players, cell phones and even video games. In one study, researchers found that 12.5 percent of kids between 6 and 19 already had measurable hearing loss.

Ear bud earphones that fit directly into the ear are the worst culprits. According to research done at Harvard, ear buds often deliver sound almost 10 decibels higher than headphones that cover the ear. That's because tiny earphones don't block out surrounding sound very well, so kids turn up the volume to dangerous levels.

To understand exactly what's happening, picture the cochlea, a seashell-shaped structure inside the ear that's filled with fluid and lined with tiny hair cells that wave gently like anemones.

The hair cells pick up sound vibrations and transmit them to the auditory nerve. When hair cells are blasted by sound, they start to look like a wheat field after a windstorm. Damage can be done both by short exposure to really loud sound or by continuous exposure to lower levels of sound.

Kids don't notice damage to hair cells because it's gradual and painless. It's also permanent. That's why parents have to step in to be sure the sounds kids hear when they are young won't compromise their ability to hear when they are older. Here's what you should do:

Learn about hearing loss. The National Institute on Deafness sponsors the Noisy Planet (http://www.noisyplanet.nidcd.nih.gov/) which includes information targeted to parents and tweens. Dangerous Decibels (http://www.dangerousdecibels.org) includes a virtual exhibit full of games that help kids understand how the ear works and how loud sounds cause damage.

Encourage young music lovers to visit websites like hearnet.com where they can watch videos by famous musicians who can no longer enjoy music because of hearing loss. Those who want to delve even deeper can explore the National Institute on Deafness and Other Communication Disorders (NIDCH) entire middle school curriculum about hearing that includes some riveting graphics in the student activity titled "Too Loud, Too Long, Too Close," (http://tinyurl.com/cltbre).

Understand decibels. Sound is measured in decibels, but decibels aren't like inches. For each 10-decibel increase, the intensity of sound doubles. Sounds over 85 decibels harm hearing but adults may not recognize dangerously loud sounds, especially if they already have hearing loss. Use NIDCD's interactive ruler to understand which sounds can be harmful (www.nidcd.nih.gov/health/education/decibel/decibel.asp). Another alternative is to purchase a sound level meter from a company like Radio Shack. The meters which cost about $50 and are a quick and definitive way to end arguments about what's "too loud."

Replace bud earphones. Earphones that cover the ear with a cushion may not be as stylish, but they are less likely to cause hearing damage. When using earphones, your child should be able to hear you when you speak to him and you should not be able to hear "bleed out" sound if you are standing three feet away.

Look for controls. When purchasing new equipment that includes headphones, check to see whether volume controls are preset at the factory. Newer models of the Apple iPod, for example, include volume control software. (A tutorial explaining how to set the controls is available at http://docs.info.apple.com/article.html?artnum=303414). For older equipment, use the Earsaver Volume Limiter (available at earplugstore.com), or mark the level of acceptable sound on the volume control with permanent marker.

Limit exposure. Set limits on how long your child is allowed to use headphones each day. Some experts recommend no more than one hour; others say that up to four hours is okay if the volume is at an appropriate level. Whenever possible, have your child listen to music over home speakers you can hear. That way you can control the volume and find out what kind of music your child enjoys.

n Use earplugs. When kids are going to be exposed to loud sounds, perhaps because they are attending a concert, seeing a loud movie or even cutting the grass, have them wear ear plugs. Although earplugs are available at drugstores, sporting goods stores and music stores, the selection is much larger at wwww.earplugstore.com. Suggest that young musicians choose brands like Hearos or Mack's Hear Plugs which reduce harmful sound without creating distortion.

n Be alert for signs of hearing loss. Temporary hearing loss or ringing in the ears is a clear indication that hair cells are in trouble and your child should find a quieter activity immediately. Remember that headphones aren't the only source of harmful sound. Even squeaky toys for babies can cause damaging levels of noise. So can loudspeakers at school dances, boom boxes and car stereos. Be sure your child understands that ears don't "get used" to loud sounds. When loud sounds become more tolerable, it's because hearing has already been damaged.

Hearing protection is something very important to me because my daughter was born deaf. She struggles every day to understand speech and other sounds that the rest of us take for granted. I had no choice about my daughter's hearing loss. If your child can hear today, you do have a choice about how well he or she will hear in the future.

Supervising your child's headphone use will probably be a hassle. One recent study at the University of Colorado actually found that teens turned the volume up when someone suggested they turn it down. Even in our household where the consequences of hearing loss are so conspicuous, my two music-loving sons often want to argue when I say, "turn it down." Despite their protests, it's an argument I'm determined to win. You should be too.