What is noise-induced hearing loss (NIHL)?
Every day, we experience sound in our environment, such as the sounds from television and radio, household appliances and traffic. Normally, we hear these sounds at safe levels that do not affect our hearing. However, when we are exposed to harmful noise - sounds that are too loud or loud sounds that last a long time - sensitive structures in our inner ear can be damaged, causing NIHL. These sensitive structures, called hair cells, are small sensory cells that convert sound energy into electrical signals that travel to the brain. Once damaged, our hair cells cannot grow back.
What sounds cause NIHL?
NIHL can be caused by a one-time exposure to an intense impulse sound, such as an explosion, or by continuous exposure to loud sounds over an extended period of time, such as noise generated in a woodworking shop.
Sound is measured in units called decibels. On the decibel scale, an increase of 10 means that a sound is 10 times more intense, or powerful. To your ears, it sounds twice as loud. The humming of a refrigerator is 45 decibels, normal conversation is approximately 60 decibels and the noise from heavy city traffic can reach 85 decibels. Long or repeated exposure to sounds at or above 85 decibels can cause hearing loss. The louder the sound, the shorter the time period before Nl HL can occur. Sounds of less than 75 decibels, even after long exposure, are unlikely to cause hearing loss.
Although being aware of decibel levels is an important factor in protecting one's hearing, distance from the source of the sound and duration of exposure to the sound are equally important. A good rule of thumb is to avoid noises that are too loud and too close or that last too long.
What are the effects of NIHL?
Exposure to harmful sounds causes damage to the hair cells as well as the auditory, or hearing, nerve. Impulse sound can result in immediate hearing loss that may be permanent. This kind of hearing loss may be accompanied by tinnitus - a ringing, buzzing, or roaring in the ears or head - which may subside over time. Hearing loss and tinnitus may be experienced in one or both ears,and tinnitus may continue constantly or occasionally throughout a lifetime.
Continuous exposure to loud noise also can damage the structure of hair cells, resulting in hearing loss and tinnitus, although the process occurs more gradually than for impulse noise.
What are the symptoms of NIHL?
When a person is exposed to loud noise over a long period of time, symptoms of Nl HL will increase gradually. Over time, the sounds a person hears may become distorted or muffled and it may be difficult for the person to understand speech. Someone with NlHL may not even be aware of the loss but it can be detected with a hearing test.
Can NIHL be prevented?
NIHL is 100 percent preventable. All individuals should understand the hazards of noise and how to practice good hearing health in everyday life:
- Know which noises can cause damage (those at or above 85 decibels).
- Wear earplugs or other hearing protective devices when involved in a loud activity (special earplugs and earmuffs are available at hardware and sporting goods stores).
- Be alert to hazardous noise in the environment.
- Protect the ears of children who are too young to protect their own.
- Make family, friends and colleagues aware of the hazards of noise.
- If you suspect hearing loss, have a medical examination by an otolaryngologist (a physician who specializes in diseases of the ears, nose, throat, head and neck) and a hearing test by an audiologist (a health professional trained to measure and help individuals deal with hearing loss).
The National Institute on Deafness and Other Communication Disorders (NIDCD) maintains a directory of organizations that can answer questions and provide printed or electronic information on NlHL. Please see the list of organizations at www.nidcd.nih.gov/directory.
Source: National Institute on Deafness and Other Communication Disorders: www.nidcd.nih.gov/health/hearing/noise.asp
