Human Sweat Cortisol Versus Blood and Saliva: Quantitative Interpretation

Measuring cortisol in sweat is being investigated as a minimally invasive approach to repeated cortisol monitoring, but its quantitative relationship with cortisol measured in blood or saliva remains uncertain. This focused critical review examined human studies that measured endogenous cortisol in sweat and in serum, plasma, whole blood, or saliva in the same participants. The aim was to determine which conclusions these comparisons support. The included studies assessed direct associations, within-person changes over time, comparisons across defined sampling windows, agreement between paired measurements, and model-based prediction. These approaches answer different questions and should not be treated as evidence of one common sweat-to-reference relationship. Sweat cortisol showed associations with blood or saliva under specific study protocols, but evidence that sweat values can be used interchangeably with blood or saliva values was limited. Predictive models were evaluated within their original datasets, but none of the identified models was tested in an independent cohort. Interpretation also depends on the analytical method, collection conditions, timing, and study design. No general conversion from sweat cortisol to blood or salivary cortisol was supported by the identified evidence. Sweat cortisol should therefore be interpreted only within the conditions and type of comparison directly evaluated.