Noise-induced hearing lose(NIHL) is characterized by bilaterally symmetrical hearing loss, but some screening audiometries of employees who were exposed noise showed asymmetry. Therefore, this study was carried out to evaluate distribution of asymmetrical hearing loss and factors influencing asymmetries.

Study subjects were 294 male employees who have participated in 1st and 2nd noise-specific health examination.

The interaural threshold difference of 20 dB or more at 4,000 Hz was classified as asymmetry. Among 294 NIHL employees. 19% had left asymmetric hearing loss. 22% had right asymmetric hearing loss. and overall asymmetry were 41%. Prevalence of asymmetry at 4,000 Hz significantly more decreased in middle(80~84 dB (A)) and high-level noise exposure groups(> or =85 dB(A)) than low-level exposure group and significantly increased as greater hearing threshold level in the worse ear. Prevalence of left asymmetry at 4,000 Hz significantly increased as greater hearing threshold level in the worse ear than right asymmetry. The interaural difference was significantly greater in the left asymmetry.

Noise exposure produced asymmetric hearing loss(interaural asymmetry was 20 dB and more in 41% of case) and left ear was more susceptible to noise demage than right ear.