Linking hair cortisol and life stress: The role of stress reactivity and habituation

BACKGROUND: Hair cortisol concentration (HCC) has emerged as a biomarker for long-term cortisol secretion, yet evidence linking HCC to self-reported life stress remains inconsistent. Although individual differences in acute stress reactivity as well as habituation may moderate this association, no research has examined how these processes interact to modulate the HCC-stress link. Moreover, most studies have relied on assessments of recent stressor exposure only, with limited attention to lifetime stressor exposure. METHOD: A final sample of 72 healthy individuals (53 women) who provided hair samples and underwent the Trier Social Stress Test three times over consecutive weeks, during which changes in salivary cortisol, cardiovascular parameters, and self-reported stress were assessed. The Stress and Adversity Inventory was administered to assess lifetime stressor exposure. RESULTS: As hypothesized, preregistered analyses showed that greater lifetime stressor exposure and acute cortisol reactivity were both associated with elevated HCC. No association was found between HCC and stress habituation, and no moderation effects on the relation between HCC and lifetime stressor exposure were observed for reactivity or habituation. Exploratory analyses revealed a consistent link between early-life stressor exposure and HCC, whereas a positive association with adulthood stressors was evident only for individuals with less cortisol reactivity. CONCLUSIONS: The results suggest that HCC reflects not only lifetime stressor exposure but is also influenced by individual differences in cortisol reactivity, highlighting its role as an integrative, yet complex biomarker of chronic stress. In contrast, the lack of an association with habituation indicates limited sensitivity to dynamic adaptation processes occurring over weeks.