Stress in the strands: Hair offers clues to children’s mental health

University of Waterloo researchers discover hair cortisol levels can predict mental health risks in chronically ill children.

From University of Waterloo 09/10/25 (first released 15/09/25)

Long-term stress levels, measured through hair samples, may provide important clues about mental health risks in children with chronic physical illnesses (CPI), according to new research from the University of Waterloo.

The study highlights how high hair cortisol, a type of steroid hormone, acts as a powerful early warning sign that could help identify children who live with CPI and who could be most at risk of mental health challenges, helping guide prevention and treatment strategies to better support their health and well-being.

An estimated 40 per cent of children in Canada live with a CPI — a number that has been rising steadily for decades.

These children face a much higher risk of developing mental health problems than their healthy peers, putting them at greater risk for poor quality of life, suicidal thoughts and increased reliance on health-care services.  
 
“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 Waterloo PhD candidate in Public Health Sciences and lead author of the study.

“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.” 
 
The study followed 244 Canadian children with chronic physical illnesses over four years, measuring stress using hair cortisol — a biological marker that reflects stress levels over time.

Researchers found that more than two-thirds of these children had persistently high cortisol levels.

Those children were also more likely to show symptoms of depression, anxiety, or other mental health concerns compared to peers whose cortisol levels decreased over time.

When the researchers compared these patterns to reports of emotional and behavioural difficulties, they found that children whose cortisol levels declined over time showed fewer symptoms of anxiety, depression and behaviour problems than those whose cortisol levels stayed high.

“Identifying these risk factors early could help doctors and families intervene before emotional and behavioural difficulties take hold,” said Dr. Mark Ferro, a professor in Waterloo’s School of Public Health Sciences and co-author of the study.

“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, Association between hair cortisol and psychopathology in children with a chronic physical illness, was recently published in Stress and Health. 

Ferro and colleagues from Waterloo and McMaster University also published new research showing that biomarkers found in the blood of children with CPI may help predict future mental health challenges.

The study, Inflammatory biomarkers predictive of psychopathology in children with physical illness, found that some blood signals were linked to children with CPI experiencing worsening mental health over time, while others were associated with improvements.

The findings suggest that routine blood tests, combined with mental health check-ups, could help doctors identify children who may need extra support earlier.