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