Noise-induced hearing loss

Hearing loss caused by noise can occur in people of any age. It may develop suddenly or gradually, depending on the source and intensity of the noise. Noise can affect hearing in several ways.

• Acoustic trauma occurs when a sudden, extremely loud sound, such as an explosion, a gunshot, or a firecracker close to the ear, damages any of the structures in the ear and produces an immediate, severe, and permanent hearing loss. This type of injury often requires immediate medical attention.
• Temporary threshold shift occurs when loud sounds (such as from a rock concert) cause a temporary ringing and hearing loss. Sounds may also seem muffled. These effects usually don't last more than a few hours, although they may sometimes last several days or weeks. Repeated exposure to sounds that cause temporary threshold shifts can gradually lead to permanent threshold shifts, commonly referred to as noise-induced hearing loss.
• Noise-induced hearing loss is the result of repeated, frequent exposure to loud or moderately loud sounds over a long period of time (often years). Though permanent, this kind of hearing loss is almost entirely preventable.

How loud a noise is and how long you are around it determine whether a noise is harmful. On-the-job (occupational) noise is one of the most common sources of harmful noise, largely because you are around it all day for years. For instance, if you work in construction, in a factory, or are in the military, you may be around harmful noise for several hours each day.

The sounds of recreation and daily activities over many years can also damage the ear and cause hearing loss. These include:

• High-volume music.
• The noise of power tools, such as chainsaws or electric drills.
• The noise from lawn mowers, household appliances (such as blenders and vacuum cleaners), and vehicles (such as snowmobiles and motorcycles).

You can reduce harmful noise levels and prevent noise-induced damage to your hearing by avoiding noisy situations whenever you can. When you can't avoid noisy situations, wear hearing protectors such as earplugs or earmuffs.

Noise-induced hearing loss is usually permanent and cannot be reversed. Hearing aids, which make sounds louder, are often helpful for this type of hearing loss.

How does noise-induced hearing loss develop?

To be heard, sound energy has to be strong enough to bend tiny hair cells in the cochlea, a part of the inner ear. The force of loud noise can damage these hair cells. A small amount of damage may have no effect on hearing. With repeated exposure to noise, however, more of the hair cells are damaged, resulting in hearing loss.

Noise-induced hearing loss usually affects both ears. However, one ear may be affected more than the other if you have had repeated, long-term exposure to a loud sound that is always coming from the same direction, such as gunfire that is always near the same ear.