Two protective measures have been investigated related to the amount of noise exposure and the duration of that exposure. Although these would be hard to regulate in spontaneous occurrences, they could have a positive effect on work conditions if guidelines could be set for machining times or for other systems that produce loud noises over a long period of time. The toughening effect is put in place by increasing the system's resistance to noise over time. Currently, the specific mechanisms that cause the cochlear toughening are not known. However, the OHCs and related processes are known to play a role. The other toughening measure is to spread a given amount of energy to the system over a longer amount of time. This would allow recovery processes to take place during the quiet interludes that are gained by increasing the exposure duration. So far, studies have not shown a direct correlation between the amount of toughening and the amount of threshold shift experienced. This suggests that even a toughened cochlea may not be completely protected.
