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Noise-induced hearing loss (NIHL) continues to be one of the most prevalent occupational conditions and occurs across a wide spectrum of industries. Occupational hearing loss is preventable through a hierarchy of controls, which prioritize the use of engineering controls over administrative controls and personal protective equipment. The occupational and environmental medicine (OEM) physician works with management, safety, industrial hygiene, engineering, and human resources to insure that all components of hearing loss prevention programs are in place.1 The OEM physician should emphasize to employers the critical importance of preventing hearing loss through controls and periodic performance audits rather than just conducting audiometric testing. Nevertheless, audiometric testing, besides documenting the permanent loss of hearing, can be of value in the identification of hearing loss at a time when early preventive intervention is possible. The American College of Occupational and Environmental Medicine (ACOEM) believes that OEM physicians should understand a worker's noise exposure history and become proficient in the early detection and prevention of NIHL.The OEM physician also plays a critical role in the prevention of NIHL by serving as a professional supervisor of the audiometric testing component of hearing conservation programs. The Occupational Safety and Health Administration defines a requirement for professional supervisors in the 1983 Hearing Conservation Amendment.2 The responsibilities of the professional supervisor can be found in the ACOEM position statement “The Role of the Professional Supervisor in the Audiometric Testing Component of Hearing Conservation Programs.”3 Responsibilities include interpretation of audiograms, work-relatedness determinations, referral of problem cases, quality oversight of audiometric testing, and determination of the effectiveness of the hearing conservation program.This position statement clarifies current best practices in the diagnosis of NIHL. On the basis of current knowledge, ACOEM proposes the following update of a previous position statement4 regarding the distinguishing features of occupational NIHL.Occupational NIHL, as opposed to occupational acoustic trauma, is hearing loss that is a function of continuous or intermittent noise exposure and duration, and which usually develops slowly over several years. This is in contrast to occupational acoustic trauma, which is characterized by a sudden change in hearing as a result of a single exposure to a sudden burst of sound, such as an explosive blast. The diagnosis of NIHL is made by the OEM physician, by first taking into account the worker's noise exposure history and then by considering the following characteristics.The principal characteristics of occupational NIHL are as follows:It is always sensorineural, primarily affecting the cochlear hair cells in the inner ear.It is typically bilateral, since most noise exposures are symmetric.Its first sign is a “notching” of the audiogram at the high frequencies of 3000, 4000, or 6000 Hz with recovery at 8000 Hz.5This notch typically develops at one of these frequencies and affects adjacent frequencies with continued noise exposure. This, together with the effects of aging, may reduce the prominence of the “notch.” Therefore, in older individuals, the effects of noise may be difficult to distinguish from age-related hearing loss (presbycusis) without access to previous audiograms.6The exact location of the notch depends on multiple factors including the frequency of the damaging noise and size of the ear canal.In early NIHL, the average hearing thresholds at the lower frequencies of 500, 1000, and 2000 Hz are better than the average thresholds at 3000, 4000, and 6000 Hz, and the hearing level at 8000 Hz is usually better than the deepest part of the notch.