It is more than a half-century since Dr. Hans Selye proposed that the reaction to an external stimulus to a human be called a “stress.” However, an index that can quantitatively evaluate the stress has not yet been established. We have focused on the change of α-amylase activity in saliva (salivary amylase) and carried out an in vivo evaluation in six normal subjects to define the levels of mental stress through amylase activity. In this evaluation, the Kraepelin Psychodiagnostic Test was used as a mental stressor for the subjects. In normal subjects, a comparatively quick response was observed by the experiment for stress load, which verified a correlation between mental stress and salivary amylase activity. The sign of gradient calculated from the salivary amylase activity was negative or positive, depending on whether the stress reaction is comfortable. Furthermore, when the salivary amylase activity and salivary total protein were measured, the effect of the salivary flow rate could be estimated. The change of salivary amylase activity was confirmed as being originated from stress. These results suggest that the monitoring of salivary amylase could be used as a noninvasive indicator of stress reaction.
