From lifetime stressor exposure to daily stress experience: Associations with hair cortisol.

Background: Although hair cortisol is an established index of long-term cumulative cortisol output, associations with chronic stress have been inconsistent, potentially due to heterogeneous and temporally misaligned stress assessments. Here, we integrate detailed lifetime stressor measures and ecological momentary assessments (EMA) to examine associations with hair cortisol and the cortisol/DHEA ratio. Methods: Two methodologically aligned studies were conducted. Study I ( Results: In Study I, neither early-life nor adulthood stressor exposure were associated with hair cortisol. In Study II, greater severity of adulthood stressor exposure was related to elevated hair cortisol concentrations, stable across time points and robust to covariate adjustment. Early-life and recent stress measures were not related to hair cortisol. Across both studies, the hair cortisol/DHEA ratio showed no consistent associations with any stress dimension. Conclusions: Our findings provide partial support for a positive association between self-reported adulthood stressor exposure and hair cortisol. However, the absence of consistent effects across both studies, despite substantial methodological overlap, echoes the heterogeneity reported in prior research. Potential reasons are discussed. Future research should address the complexity of individual stress exposure, incorporate hair cortisol into multimethod HPA axis assessments, and advance methodological standardization.