Now Hear This: iPods May Cause Hearing Loss!

The iPod has quickly become a cultural icon. Gone are the days when teenagers jived to the sounds of a big-band orchestra heard over a RCA radio or from a Victrola. We no longer see a child with a single earphone listening to the tinny sound of an AM transistor radio. Boomboxes are now passé. The music of the 21st century is now listened to through in-the-ear buds connected to a personal listening device. And the music played loud! In fact, it is usually too loud for the health of our hearing.

There is mounting evidence that listening to loud music for long periods of time can lead to hearing loss, called noise-induced hearing loss (NIHL). The site of injury is believed to be the hearing receptor cells in the inner ear called hair cells. Ambient sound waves vibrate the eardrum and bones of hearing, which produces pressure waves in the fluid of the inner ear. These waves deform the delicate projections of the hair cell and stimulate the hair cell to ‘fire’ and excite the nerve of hearing.

Excessively loud sounds can cause extreme deformation of those hair cells and damage them, sometimes irreparably, if the sound is sufficiently loud or present for an excessively long time. The hair cells that respond to high-frequency sounds are the most susceptible to damage, making this the most common range for noise-induced hearing loss.

While more than 30% of Americans over the age of 20 (55 million) have lost some high frequency hearing, 17% of adults aged 20-69 (approx. 26 million) have permanent hearing damage due to noise exposure. Early hearing loss is even being recognized in children, most likely as a result of noise trauma. One study in the United States found that 12.5% of children 6 to 19 years of age have NIHL—that’s approximately 5.2 million kids!

Sound loudness is measured in units called decibels (dB), with 0 dB being the quietest sound that the average human ear can detect. The scale is logarithmic, such that a 3 dB increase in loudness is functionally a doubling of sound energy. Conversational speech usually falls in the 50-60dB range. Prolonged exposure to sound levels greater than 85dB has been shown to cause hearing loss in most people, and louder levels can cause a more accelerated damage. Recognizing this risk, the Occupational Safety and Health Administration (OSHA) has regulated workplace exposure to noise, restricting workers to noise exposure time of 8 hours daily at 90dB, with a halving of exposure time for each 5dB increase (i.e., 4 hours at 95dB, 2 hours at 100db, etc.). The highest permissible industrial noise exposure for an unprotected ear is 115dB for 15 minutes per day, after which permanent damage is likely to occur.

The iPod and other similar personal listening devices can produce maximal sounds of approximately 130dB, enough to cause injury quickly. Listening to music at 75dB is considered safe, but prolonged exposure to music louder than 85 dB can lead to hearing loss and tinnitus (ringing in the ears).

Audiologist studies have estimated that individuals play music at hazardous levels approximately 5 to 25 percent of the time. Recognizing this, Apple (the maker of the iPod) has issued warnings of the risk of permanent hearing loss if earphones or headphones are used at high volume. The newest generations of iPods and iPhones even have a software option to allow a user (or a parent) to limit the volume output and to lock it in with a passcode. In Europe, many personal listening devices are limited to 100dB output by French law.

The damage of NIHL is not only caused by how loud the sound and how long the ear is exposed, but also depends on how much time passes between noise exposures. After all, it takes time for the hair cells can recuperate from the previous injury. Apple owns a patent for software that would automatically calculate how long a person has been listening, and at what volume, before automatically reducing the sound level. The device could also calculate the amount of “quiet time” between when the iPod was turned off and restarted, and then allow the volume to increase again to a safe level. Currently, however, this feature is not available.

While continuous listening at 75dB may be considered safe for most individuals, when background noise is present it may not be loud enough for listening pleasure. The louder the background noise, the louder the music tends to be played, thus increasing the risk for hearing damage. Also contributing to elevated listening levels is a neural phenomenon that adapts the auditory system to the intensity of sound. The brain perceives that the sound intensity is lessening, so the listener turns up the volume.

A study in Britain found that nearly 20 percent of teenagers were listening to music for more than 21 hours a week, which averages 3 hours per day. A separate study estimated that use of an iPod with standard earbuds, played at 90% of maximum volume for 2 hours daily, 5 days a week, will produce a 40dB (moderate) hearing loss in the high frequencies over a 10-year period. The high frequencies of hearing are those that impart the consonant phenomes of speech, making understanding the meaning of speech more difficult if these frequencies are lost. So what can be done to safeguard the hearing of our children?

First, they should be educated on the risks and options available to lessen the likelihood of hearing injury. For many years, the British Health Ministry has been supporting an education program called “Don’t Lose the Music.” In the United States, a program entitled “Dangerous Decibels” demonstrated the ability of 4th and 7th grade students to understand, retain, and process the risks of noise exposure after just one brief interactive session. While the 4th graders maintained their healthier behaviors at the time of a follow-up (three months later), the 7th graders’ habits regressed, suggesting the need for periodic reinforcement. It should be reinforced to our children that if someone can hear sound “leaking” from earphones several feet away, it’s probably too loud. Limit the time of listening at high volumes, and afterward give the ears a chance to recover. If there is ringing in the ears, a feeling of fullness in the ears, or if speech is difficult to understand after a listening session, then the music was too loud.

Second, technology can be helpful. In addition to the output power limitation on an iPod, there are child-safe earphones and earbuds available at reasonable prices. These limit the absolute volume they will produce. The iHearSafe Earbuds, for example, limit the volume to 80dB. Also helpful are earphones that block out background noise, such as over-the-ear earphones, and especially noise-canceling earphones that use electronics to actively reduce ambient noise. By lessening background noise, music can be enjoyed at lower and safer volumes, and can extend listening time.

We must also recognize that our children may be exposed to loud noise in many other ways. Live rock concerts or music by a DJ are often presented at dangerously high volume levels, frequently over 120dB. Musical instruments such as the violin and viola can produce loud high-frequency sounds very near the musician’s ear. Children’s toys that produce loud noises may often be close to the ears due to children’s short arms. The Sight and Hearing Association (www.sightandhearing.org) publishes a list of these dangerous toys yearly. It is important to be vigilant in all aspects of our lives to preserve our hearing and communication ability.