Noise-Induced Hearing Loss (NIHL): literature review with a focus on occupational medicine

According to the Ministry of Health (2006), Noise-Induced Hearing Loss (NIHL) is hearing loss caused by prolonged exposure to noise. It is characterized as sensorineural hearing loss and is usually bilateral, irreversible, and progressive while the exposure to noise continues. A NIHL is a predictable and preventable disease with an epidemiologically relevant prevalence in urban communities. The hearing loss begins and predominates in the frequencies of 3, 4, and 6 kHz and eventually progresses to 8, 2, 1, 0.5, and 0.25 kHz. In Brazil, regulatory standard 15 limits the exposure to continuous noise to no more than 4 hours' exposure to 90 dBA and a maximum level of 85 dB for a full 8-hour working period. As NIHL is a preventable and predictable disease, preventive action by professionals may be able to change the prevalence of hearing loss in noisy environments.