Noise and Hearing Loss
Noise induced hearing loss (NIHL) is a condition that occurs when
the ear is exposed to excessive levels of noise. When we hear, tiny
sensory hair cells in the cochlea pick up sound vibrations, convert them
into electrical signals and send the signals to the auditory nerve,
then on to the brain for processing. Loud noise permanently damages the
hair cells, reducing the ability to get sound signals to the brain. NIHL
can occur suddenly, after a very loud noise, like an explosion, or
slowly, through accumulated damage. In severe cases, the damage can be
significant enough to greatly impair hearing.
Sound is measured in terms of decibels (dB), ranging from 0 (the
faintest sound detectable by human ears) to over 180 (the sound of
launching rocket). 30 dB is about the equivalent of a whisper. Normal
conversation is about 60 dB. A kitchen blender has a sound level of
about 90 dB. Many power tools (like a drill or chainsaw) operate at 100
dB. Sounds at 140 dB or higher include a gun shot, fireworks, and jet
engine.
Generally, sustained exposure to sounds of 85 dB or higher can cause
NIHL. Signs of hearing loss generally occur over time. Patients may
experience tinnitus (ringing in the ears), distorted or muffled sounds,
and difficulty understanding speech. Initially, the symptoms may be
temporary (called a temporary threshold shift), lasting from 16 to 48
hours. Eventually however, with continued exposure to loud noise, the
symptoms don't go away.
NIHL is fairly common. The Centers for Disease Control and
Prevention estimates 17 percent of adults in the U.S. (approximately 26
million people) have some degree of NIHL. The condition also affects
12.5 percent of children and adolescents in this country.
Music and Hearing Loss
Federal regulations help protect hearing of workers who are exposed
to dangerous levels of noise. However, there are no regulations for the
general public. One important source of excess noise for many people is
music players. Researchers report most portable music players can play
sounds reaching 100 to 110 dB. Maximum sound output of the popular iPod
has been measured at 115 dB. Researchers say the earbud-style earphones,
which keep sounds inside the ears, can increase the sound intensity of
portable music players by roughly another 5 dB.
College Concerns
Investigators at University of Florida in Gainesville have been
screening college students for eligibility to participate in
hearing-related studies. When the researchers tested the students'
hearing, 25 percent of the volunteers were found to have a hearing loss
of at least 15 dB. Speech & Hearing Researcher, Colleen Le Prell,
Ph.D., says this level of hearing loss is believed to be high enough to
cause significant problems with speech understanding and thus, possibly
interfere with classroom learning. In addition, roughly 8 percent of the
potential participants had hearing loss of 25 dB, which is considered
the mark of mild hearing loss. More importantly, Le Prell says, all of
those who were found to have hearing loss believed they had normal
hearing, so they were completely unaware of their hearing deficit.
Further investigation found use of personal music players to be a key
factor in the hearing loss for college students, especially for males.
Currently, University of Florida researchers are working on a drug
that may help protect the hearing structures from NIHL. In the meantime,
Le Prell says it's important to educate all children and adults on the
dangers of listening to loud music because there's no way to fix the
damaged hair cells. Hearing aids can help patients with mild degrees of
hearing loss, but won't benefit those with significant NIHL. Those with
severe NIHL may require a cochlear implant.
Research compiled and edited by Barbara J. Fister
AUDIENCE INQUIRYFor general information about noise-induced hearing loss and prevention tips:
American Academy of Audiology, http://www.audiology.org
American Academy of Otolaryngology - Head and Neck Surgery, http://www.entnet.org
American Hearing Research Foundation, http://www.american-hearing.org
American Speech, Hearing and Language Association, http://www.asha.org
Centers for Disease Control and Prevention, http://www.cdc.gov/healthyyouth/noise
Dangerous Decibels, http://www.dangerousdecibels.org
National Institute of Deafness and Other Communication Disorders, http://www.nidcd.nih.gov
BIBLIOGRAPHYIf you need a list of the research titles supporting this story, please contact Barbara Fister at (610) 395-1300 ext. 238.
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