Benign vocal fold lesions (BVFLs) are a complex of common otolaryngological diseases that cause voice problems; their prevalence in previous population-based studies was reported to be 7%–12% [1,2]. BVFLs include laryngitis, which accounts for the largest proportion, as well as vocal nodules, vocal polyps, vocal cysts, and Reinke’s edema. The main pathogenetic mechanism of all BVFLs is vibratory injury to the vocal folds caused by excessive voice use. Voice abuse often occurs in individuals with expressive and talkative personalities [3], people in educational occupations such as teachers, and those who work in noisy environments [4,5].

With industrialization, noise pollution from the surrounding environment, such as machinery, generators, traffic, and airplanes, has become a serious problem, leading to a decrease in mental health and quality of life [6,7]. Furthermore, noise pollution causes communication problems in daily life [8]. People living or working in loud environments must compensate by increasing the intensity of their voices to communicate [9]. It has been reported that voice disorders and vocal fold lesions can be caused by voice abuse necessitated by a noisy environment [10]. However, most studies investigating risk factors for BVFLs have been limited to specific occupational groups. Large-scale studies differentiating among vocal fold lesions through laryngoscopic examinations are lacking.

Therefore, we analyzed the risk factors for BVFLs using population-based data from a survey of the general public, not specific occupational groups. The purpose of this study was to investigate the relationship between a history of noise exposure in the workplace and BVFLs.

The survey protocol was approved by the Institutional Review Board of the Korean Centers for Disease Control and Prevention (KCDCP; No. 2010-02CON-21-C, 2011-02CON-06-C, and 201201EXP-01-2C). All participants provided informed consent at baseline.

In our study, 8.4% of the noise-exposed group showed BVFL findings on laryngoscopy. Laryngitis accounted for the largest proportion of BVFLs, with a prevalence of about 5.3%. BVFLs were about 1.5 times more likely to occur in the noise-exposed group than in the unexposed group after adjustment for confounding variables. Our results suggest that noise exposure in the workplace could be a risk factor for BFVLs. More than 100 years ago, the French otolaryngologist Etienne Lombard reported the Lombard effect, by which speech amplitude involuntarily increases when background noise increases [11]. Moreover, apart from that effect, if noise in the surrounding environment interferes with communication, excessive voice effort might intentionally be made to compensate for the background noise [9]. Our study is the first population-based study to confirm through laryngoscopy that BVFLs could be caused by working in a noisy environment.

The vocal fold is anatomically divided into five layers. The surface of the vocal fold has a stratified squamous epithelium that can withstand the stress of vocal fold vibration. Deep below it is the lamina propria, which is further divided into three layers [12]. The superficial layer of the lamina propria is Reinke’s space, which is filled with extracellular matrix composed of collagen, elastin, and hyaluronic acid and plays an important role in voice production through vocal fold vibration [13,14]. The regular vibrations of Reinke’s space periodically close the vocal folds and produce the voice [15]. Vibrations that are too strong or that continue for a long period of time cause vascular congestion and swelling in the middle of the vibrating part of the vocal fold [3]. If voice abuse continues chronically, lesions such as laryngitis, nodules, polyps, cysts, and granulomas occur in the region affected by submucosal edema. It has been proposed that a glottic sulcus forms after any cyst is naturally emptied, which causes the vocal fold to become less flexible and the physical volume to decrease, increasing the effort required to operate the vocal fold [15].

Analyzing and managing risk factors for BVFLs are essential for treating and preventing them. Vibratory trauma is the most common risk factor for voice disorders, and the frequency of its occurrence in people with occupations requiring extensive voice use was reported to be high. In Poland, it was reported that occupational voice disorders accounted for about 20% of all occupational diseases [16]. In addition, lifestyle habits (e.g., smoking, alcohol consumption, and caffeine intake) and chronic medical conditions (e.g., gastroesophageal reflux disease and obesity) have also been reported to be associated with BVFLs and voice disorders [17-21]. In population-based data provided by the National Health Insurance Service of South Korea, middle-aged individuals showed the highest prevalence of BVFLs, which is similar to our results in this study. However, in the 2014 data of that study, the peak age of prevalence shifted from the 50s to the 60s compared with previous data [1]. That was judged to reflect an increase in the healthy life expectancy. Although middle-aged people are still active in social activities, their neuroendocrine function might be deteriorating, and various diseases could develop as a result of abnormal cortisol secretion in response to stress [22]. The high incidence of BVFLs in middle-aged people is thought to be related to that process, but this possibility has not been clearly established.

The study of Rontal et al. [23], in which 283 workers in a noisy environment underwent laryngoscopy, reported that 21 patients (8%) showed laryngitis, vocal nodule, or vocal polyp findings. Most of the participants in that study were smokers, and although voice abuse in the workplace was considered to be the main cause, excessive dust and fumes in the workplace were considered to be a secondary cause. They recommended that future studies consider aspects related to mental health, such as stress caused by noise,. We found no significant differences in the mental health items (moderate to severe stress perception, depression for more than 2 weeks within the past year, and suicidal ideation within the past year) between participants with and without occupational noise exposure, so we did not consider these variables. Rontal et al. [23] found that workers in noisy environments showed a 30% recurrence rate after laryngeal surgery and argued that a high possibility of treatment failure due to continuous voice abuse could be a risk if the work environment is not considered. That result supports the importance of reducing noise levels in workplace environments.

Several previous studies have reported hearing loss, cardiovascular disease, premature birth, and other medical conditions as diseases that can be caused by occupational noise exposure [24]. Based on that clinical evidence, institutional arrangements and environmental standards for working environments have been made. However, awareness of vocal fold diseases caused by noise exposure is still lacking, even though it was first pointed out in the 1970s [23]. Voice problems tend to be overlooked clinically because they do not affect patients’ livelihood or cause substantial discomfort. Many patients with voice problems are unaware of treatment options or expect their symptoms to improve on their own, with only a small number of patients receiving professional treatment for their voice problems [25]. If vocal fold disease is left unattended, a vicious cycle of increasing vocal effort can occur. That cycle can be prevented by managing vocal hygiene, so it is important to know that BVFLs can be an occupational disease not only in occupations that require extensive voice use but also among general workers in noisy environments. We found associations between occupational noise exposure and BVFLs in terms of prevalence; although those findings do not indicate a causal relationship, they merit attention because the relationship between occupational noise exposure and BVFLs has been overlooked clinically. In the data we used from the fifth KNHANES, 19,937 people with and without laryngoscopy data indicated whether they were exposed to noise, and 10.6% of them responded that they had been exposed to work noise for more than 3 months. Because the frequency of occupational noise exposure in the general population is high, it is important to recognize the risk of vocal fold diseases among workers exposed to noisy environments. Precautions when talking in a work environment, voice hygiene education, measures to promote rapid self-awareness of voice problems, and regular screening should be recommended [26]. If vocal cord-related symptoms appear, medical staff should advise the worker to undergo laryngoscopy during a prompt specialist examination.

Our study has several limitations. First, as a cross-sectional study, it cannot clearly explain the causal relationship between occupational noise exposure and BVFLs. In our study, we suggested voice abuse as an explanation for the association between occupational noise exposure and BVFLs, but voice abuse is not the only pathophysiology of BVFLs, and other possibilities should be carefully considered. Second, a major limitation is that we did not have access to information about noise intensity or accumulated exposure time. The exposure history survey relied on self-reports by the participants. Third, the various occupations of the study subjects were divided into three groups for analysis. Although our results were statistically insignificant, this does not mean there is no association between occupation and BVFLs. Several studies have clinically confirmed associations between specific occupational groups and voice disorders. Given our results, we suggest that a large-scale prospective study is needed to determine the prevalence of BVFLs in objectively evaluated noise exposure environments and workers.

Clinicians should consider environmental noise in the workplace as a potential communication problem and understand that high environmental noise levels can contribute to voice abuse through increased vocal effort. Early diagnosis and screening for voice problems and vocal fold diseases could be necessary for workers in noisy environments, and social awareness of this association needs to be improved.