Effects of shift work and intermittent noise exposure on hearing: mechanisms and prophylactic potential.

It is well established that intermittent noise exposure characteristically produces less hearing loss than equal energy/intensity continuous noise in animal models. Ongoing different shift work regimes open for direct studies on hearing effects of intermittent noise exposure in man without ethical concern. Amazingly, few such studies are reported. In one recent study in the present volume, noise-exposed employees working 12 hours a day for two consecutive days followed by two days off, the cycle then repeated, had significantly lower permanent hearing loss than employees working nine-hour shifts from 8 am to 5 pm Monday to Friday. This commentary refers to the few studies reported, gives a short overview of the mechanisms behind noise-induced hearing loss and the protective effect of intermittent exposure, and concludes that direct studies in man on the effects of different shift work regimes on occupational hearing loss under specified noise conditions represent a prophylactic potential that calls for increased research activity. Such studies might pave the way for direct use of more optimal intermittent noise exposure regimes in future design of the noise exposure workday/-week and make future hearing conservation programs more effective.