Noise-induced hearing loss evolution: influence of age and exposure to noise.

The aims of this study were to evaluate the influence of age and exposure to noise in determining the evolution of hearing loss after noise-induced hearing loss has been already established and to define the further evolution of presbycusis. This is a cross-sectional study based on the evaluation of pure-tone audiometry threshold on 568 subjects affected by noise-induced hearing loss and exposed to noise for at least 10 years; noise exposure at testing was 85-90 dB Leqd(A). The further evolution of hearing loss was found to be more related to age than to noise exposure and was significantly less than expected for presbycusis. In conclusion our data support the hypothesis that once NIHL has manifested, it tends to worsen slightly with continued noise exposure and that progressive hearing loss is chiefly due to aging. However, in individuals with NIHL, age-related hearing loss is significantly less at frequencies damaged by noise than in non-noise-exposed individuals.