Relationship Between Salivary Cortisol and Psychological Scales in the Stress Assessment of Shift Workers: A Narrative Review

Background/Objectives: Cortisol, a stress-related protein found in saliva, is occupying an increasingly crucial role in stress research. While stress was previously assessed solely using psychological scales, the addition of cortisol as a biomarker has enabled more accurate stress assessment. Previously, stress among shift workers was evaluated both subjectively and objectively using psychological scales and cortisol levels. However, the variety of available psychological scales led to a lack of consensus on which ones should be used. This study reviewed papers investigating the relationship between cortisol and psychological scales to determine which ones should be used together. Methods: We searched for original research papers examining the relationship between psychological scales and cortisol levels among shift workers during a 20-year period from 1 January 2006 to 31 December 2025. The data were organized using psychological scales. Results: In total, 308 papers were selected, and after excluding those that met the exclusion criteria, 19 were chosen. Across the 19 studies, 10 different psychological scales were associated with cortisol. The most frequently associated psychological scales with cortisol were the Maslach Burnout Inventory (MBI), which appeared in four out of seven studies, followed by the Visual Analog Scale and Zung Self-Rating Depression Scale, which appeared in one out of two studies. Conclusions: We believe that the MBI is the most appropriate stress scale to evaluate in conjunction with cortisol; however, further evaluation is needed, particularly research that measures salivary cortisol and stress-related psychological scales using appropriate sampling methods.