Hair cortisol concentration and adolescent mental health: Insight from the Queensland Twin Adolescent Brain Project

Adolescence is a stress-sensitive period for neurodevelopment and mental health, with chronic stress implicated in the onset of psychological disorders. Hair cortisol concentration (HCC) serves as a non-invasive biomarker of long-term hypothalamic-pituitary-adrenal (HPA) axis activity, yet its relevance to adolescent mental health remains inconsistently characterised.

This longitudinal study examined HCC in 302 community-dwelling adolescent twins from Brisbane, Australia, with data collected at two sessions approximately two years apart, following a standardised assessment protocol. Three cm long hair samples were analysed to quantify cumulative stress exposure over three months, and participants completed self-reported measures of depression, anxiety, daily stress, social support, and adverse childhood experiences (ACEs). Linear mixed-effects models and quantile regression were used to examine mean-level and distributional associations between HCC and psychological and environmental variables.

Average HCC decreased significantly between sessions, with no main effect of sex, twin zygosity, or pubertal stage. In males, a higher average HCC at the second session was associated with elevated general anxiety, whereas in females, a higher average HCC was linked to higher exposure to severe lifetime stress. No associations were found between average HCC and ACEs.

These findings suggest that average HCC, reflecting cumulative cortisol secretion over the three months before each assessment, provides a stable measure of long-term cortisol in adolescents, although its associations with psychosocial stressors were limited in this cohort. Rather than functioning as a broadly sensitive biomarker of chronic stress, HCC may capture specific stress-related processes in certain subgroups, and its utility may depend on the type, timing, and chronicity of stress exposure.