A simple haircut may reveal more than just split ends. By testing for the stress hormone cortisol, which is stored in hair, researchers can identify kids with chronic illness who face the greatest risk of anxiety, depression, or behavioral struggles.
A 2025 study estimated that, globally, one in four children is living with a chronic illness, with prevalence estimates ranging from 10% to 30%. Living with chronic physical illness (CPI) presents multiple challenges, from symptom management to mental well-being and increased risk of depression and anxiety, to the social impact.
A new study led by researchers at the University of Waterloo in Canada sought to understand how long-term stress, measured through cortisol in strands of children’s hair, relates to mental health problems in kids with CPIs like type 1 diabetes, juvenile arthritis and epilepsy.
“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 lead author Emma Littler, a Waterloo PhD candidate in Public Health Sciences. “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.”
Cortisol is a steroid hormone produced by the adrenal glands, which sit on top of the kidneys. It helps regulate the body’s response to stress, but also controls essential bodily functions like blood sugar, blood pressure, inflammation, metabolism, and sleep-wake cycles. Cortisol circulates in the blood, and small amounts of it get deposited into growing hair. Because hair grows steadily, it acts like a “timeline” of stress exposure.
On average, scalp hair grows about 1 cm (0.4 in) per month. So, a 1-cm segment of hair closest to the scalp represents roughly the last month of cortisol exposure. A 3-cm (1.2-in) segment represents around three months, and so on. Hair cortisol concentration is a relatively new, non-invasive way to measure stress over months, rather than just minutes or hours.
The study examined 244 children aged two to 16 with a CPI and followed them for 48 months. Hair samples were collected up to five times over four years. The researchers usually cut a 3-cm lock of hair from the back of the head, right at the scalp. Parents completed questionnaires about their child’s mental health symptoms, both internalizing such as depression and anxiety and externalizing such as ADHD or behavioral issues. The researchers used a statistical approach called latent class growth analysis to identify different “trajectories,” or patterns over time, of cortisol levels, and then examined how these patterns related to mental health outcomes.
The children’s cortisol patterns fell into three groups: hypersecretion (68%), characterized by consistently high cortisol; hyposecretion (9%), characterized by consistently low cortisol; and hyper-to-hypo (23%), where cortisol levels started high and then decreased to normal levels. Children in the hyper-to-hypo group had fewer mental health problems (both internalizing and externalizing symptoms) than those in the hypersecretion group. Children in the hyposecretion group showed no significant difference in mental health symptoms compared to the consistently high-cortisol group.
Overall, having chronically high cortisol seemed to be linked to a greater risk of mental health issues. Which makes sense, considering prior research into the deleterious effects of stress. Other facts mattered, too: higher disability scores, being female, and certain parent characteristics were linked to worse outcomes.
The study has some limitations. Most children were White, from relatively advantaged families, and recruited from one Canadian hospital. This limits generalizability. Additionally, there was no healthy control group. The study only looked at children with chronic illness, so comparisons to healthy kids are indirect. The broad age range of the participants spans key developmental stages, and the effects of puberty weren’t measured.
Nonetheless, this method of tracking hair cortisol over time may help identify children at higher risk for developing depression, anxiety, or behavioral problems and allow targeted support to be provided to kids with consistently high cortisol levels. The study also notes mindfulness-based interventions may help lower cortisol and improve outcomes in children.
“Identifying these risk factors early could help doctors and families intervene before emotional and behavioral difficulties take hold,” said Dr Mark Ferro, a co-author on the study and an associate professor in the University of Waterloo’s School of Public Health Sciences. “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 journal Stress and Health.
Source: University of Waterloo
