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Long-term stress in hair points to mental health risks
High levels of hair cortisol reveal hidden mental health risks in children with chronic illnesses, offering doctors a non-invasive tool to predict and prevent future emotional challenges. Credit: Shutterstock
A new longitudinal study from the University of Waterloo shows that measuring cortisol in hair — a marker of cumulative stress exposure — can help predict which children living with chronic physical illnesses (CPI) are most likely to develop anxiety, depression, or behavioral problems. The research tracked 244 Canadian children over four years and linked persistent high hair cortisol to increased mental health symptoms, while declining cortisol levels were associated with improved emotional outcomes.
Scientific background and methods
Cortisol is a steroid hormone produced by the hypothalamic–pituitary–adrenal (HPA) axis in response to stress. Unlike blood or saliva measures that capture short-term fluctuations, hair cortisol provides a retrospective index of circulating cortisol over weeks to months because hair grows slowly and incorporates hormones. This makes hair sampling a non-invasive way to monitor chronic stress exposure in pediatric populations.
Researchers collected hair samples and standardized behavioral assessments from children with a range of CPIs, including asthma, diabetes, and autoimmune disorders, at multiple points across four years. Using longitudinal analysis, they identified distinct cortisol trajectories: persistently high, declining, or lower stable levels. More than two-thirds of participants showed persistently elevated hair cortisol across the study period.
Key discoveries and implications
Children whose hair cortisol remained high were more likely to show symptoms of anxiety, depression, and conduct or behavioral problems compared with peers whose cortisol levels fell over time. When cortisol declined, emotional and behavioral symptoms tended to decrease as well, suggesting that hair cortisol trajectories reflect clinically meaningful changes.
"Living with a chronic illness means facing daily challenges such as taking medications, missing school and adjusting activities, all of which can take a serious emotional toll," said Emma Littler, a University of Waterloo PhD candidate and lead author. "Our findings suggest that chronically high stress, measured through hair samples, could help identify children with CPI at the highest risk for developing mental health problems. This opens the door to earlier and more targeted support."
Dr. Mark Ferro, co-author and professor in Waterloo's School of Public Health Sciences, added: "Hair cortisol offers a non-invasive, easy-to-collect biomarker that could one day be used to screen children and track whether treatments or support programs are helping to reduce stress." The study was published in the peer-reviewed journal Stress and Health under the title "Association between hair cortisol and psychopathology in children with a chronic physical illness."
Related biomarker research
The Waterloo team, collaborating with researchers at McMaster University, also reported complementary findings from blood-based biomarker studies. That separate investigation identified inflammatory markers in routine blood tests that correlated with later mental health trajectories: some cytokine patterns predicted worsening psychopathology, while others were linked to recovery. Together, hair cortisol and blood biomarkers indicate a path toward integrated biological screening plus mental health assessment for children with CPIs.
These findings support a model in which routine, minimally invasive testing (hair and blood samples) could be added to pediatric care for children with chronic illness to flag those who may benefit from early psychological or social interventions. Early detection could reduce long-term morbidity, limit school disruption, and lower downstream health-care utilization.
Expert Insight
Dr. Ana Morales, a fictional but plausible pediatric behavioral health specialist, comments: "Biomarkers like hair cortisol give clinicians an objective signal that complements parent and clinician reports. For children with chronic illnesses, this could shift practice from reactive to proactive care — identifying stress-related risk before a full psychiatric disorder emerges and directing resources, such as cognitive-behavioral therapy or family support, where they are most needed."
Practical considerations and future prospects
Before hair cortisol can become a routine screening tool, several issues require standardization: laboratory assay methods, hair-segment sampling protocols, and normative reference ranges across ages and hair types. Researchers also need to confirm findings across diverse populations and clinical settings, and to test whether interventions guided by biomarker screening actually reduce psychiatric outcomes.
If validated, the combined use of hair cortisol and targeted blood biomarkers could transform pediatric care for children with chronic physical conditions by enabling precision prevention — matching psychosocial resources to biological risk profiles and tracking treatment response objectively.
Conclusion
This University of Waterloo study provides strong evidence that hair cortisol trajectories are linked to mental health outcomes in children with chronic physical illnesses. Persistent high cortisol identified a subgroup at elevated risk for anxiety, depression, and behavioral difficulties, while declining cortisol predicted fewer emotional problems. Coupled with blood biomarker research, these results point toward feasible, non-invasive screening strategies that could support earlier, more targeted interventions to protect the mental health of children living with chronic disease.
Source: sciencedaily
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