Noise-induced hearing loss (NIHL) is a hearing impairment resulting from exposure to loud sound. People may have a loss of perception of a narrow range of frequencies or impaired perception of sound, including sensitivity to sound or ringing in the ears. When exposure to hazards such as noise occurs at work and is associated with hearing loss, it is referred to as occupational hearing loss. Hearing may deteriorate gradually from chronic and repeated noise exposure (such as loud music or background noise) or suddenly from exposure to impulse noise, which is a short high intensity noise (such as a gunshot or airhorn). In both types, loud sound overstimulates delicate hearing cells, leading to the permanent injury or death of the cells. Once lost this way, hearing cannot be restored in humans. There are a variety of prevention strategies available to avoid or reduce hearing loss. Lowering the volume of sound at its source, limiting the time of exposure, and physical protection can reduce the impact of excessive noise. If not prevented, hearing loss can be managed through assistive devices and communication strategies. The largest burden of NIHL has been through occupational exposures; however, noise-induced hearing loss can also be due to unsafe recreational, residential, social and military service-related noise exposures. It is estimated that 15% of young people are exposed to sufficient leisure noises (i.e. concerts, sporting events, daily activities, personal listening devices, etc.) to cause NIHL. There is not a limited list of noise sources that can cause hearing loss; rather, exposure to excessively high levels from any sound source over time can cause hearing loss.
Signs and symptoms The first symptom of NIHL may be difficulty hearing a conversation against a noisy background. The effect of hearing loss on speech perception has two components. The first component is the loss of audibility, which may be perceived as an overall decrease in volume. Modern hearing aids compensate for this loss with amplification. The second component is known as "distortion" or "clarity loss" due to selective frequency loss. Consonants, due to their higher frequency, are typically affected first. For example, the sounds "s" and "t" are often difficult to hear for those with hearing loss, affecting clarity of speech. NIHL can affect either one or both ears. Unilateral hearing loss causes problems with directional hearing, affecting the ability to localize sound.
Temporary and permanent hearing changes PTS (Permanent Threshold Shift) is a permanent change of the hearing threshold (the intensity necessary for one to detect a sound) following an event, which will never recover. PTS is measured in decibels. TTS (Temporary Threshold Shift) is a temporary change of the hearing threshold due to the hearing loss that will be recovered after a few hours to a couple of days. Also called auditory fatigue. TTS is also measured in decibels. In addition to hearing loss, other external symptoms of an acoustic trauma can be:
Tinnitus Otalgia Hyperacusis Dizziness or vertigo; in the case of vestibular damages, in the inner-ear
Tinnitus
Tinnitus is described as hearing a sound when an external sound is not present. Noise-induced hearing loss can cause high-pitched tinnitus. An estimated 50 million Americans have some degree of tinnitus in one or both ears; 16 million of them have symptoms serious enough for them to see a doctor or hearing specialist. As many as 2 million people become so debilitated by the unrelenting ringing, hissing, chirping, clicking, whooshing, or screeching that they cannot carry out normal daily activities. Tinnitus is the largest single category for disability claims in the military, with hearing loss a close second. The third largest category is post-traumatic stress disorder, which itself may be accompanied by tinnitus and may exacerbate it.
Quality of life NIHL has implications on quality of life that extend beyond related symptoms and hearing ability. The annual disability-adjusted life years (DALYs) were estimated for noise-exposed U.S. workers.[20] DALYs represent the number of healthy years lost due to a disease or other health condition. They were defined by the 2013 Global Burden of Disease (GBD) Study. The DALYs calculation accounts for life limitations experienced because of hearing loss as a lost portion of a healthy year of life. The results indicate the number of healthy years lost by a group of people over a specific time period. The National Institute for Occupational Safety and Health (NIOSH) used DALYs to estimate the impact of hearing loss on quality of life in the CDC Morbidity and Mortality Weekly Report article "Hearing Impairment Among Noise-Exposed Workers in the United States, 2003-2012." It reported that 2.5 healthy years were lost each year for every 1,000 noise-exposed U.S. workers because of hearing impairment (hearing loss that impacts day-to-day activities). These lost years were shared among the 13% of workers with hearing impairment (about 130 workers out of each 1,000 workers). Mining, Construction, and Manufacturing workers lost more healthy years than workers in other industry sectors; specifically and respectively in those sectors, 3.5, 3.1, and 2.7 healthy years were lost each year for every 1,000 workers.
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