Children with chronic illnesses face extra challenges, and measuring stress through hair samples may help doctors predict which kids are at highest risk for mental health problems.

Researchers studied 244 Canadian children with chronic physical illnesses such as diabetes, arthritis and cystic fibrosis. Over four years, the team measured cortisol — a hormone released during stress — using hair samples.

Cortisol is a chemical marker that reflects stress over time.

More than two-thirds of the kids had consistently high cortisol levels. Those children were more likely to develop symptoms of anxiety, depression or behavior problems than peers whose cortisol levels declined over time, the study found.

“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,” lead author Emma Littler said in a news release. She’s a doctoral candidate in Public Health Sciences at the University of Waterloo in Ontario, Canada.

The study also found that children whose stress hormone levels decreased showed fewer emotional and behavioral symptoms.

“Identifying these risk factors early could help doctors and families intervene before emotional and behavioral difficulties take hold,” study co-author Mark Ferro, a professor of public health sciences at the university, explained.

He added that hair cortisol is “non-invasive and easy to collect” and could one day be used to track whether treatments are reducing stress.

Nearly 40% of Canadian children live with a chronic illness, researchers noted, putting them at higher risk for poor quality of life, suicidal thoughts and greater use of health care services.

The study was recently published in the journal Stress and Health. 

In related research, the team also found that certain blood biomarkers may help predict whether mental health symptoms worsen or improve in children with chronic illnesses.