A new test could predict which children are at risk for depression later in life.
Scientists at the University of Cambridge studied 1,800 teenagers in the United Kingdom suffering from mild depression.
Doctors measured a stress hormone called cortisol using saliva samples and surveyed them for symptoms of depression.
After two years, teens who had higher levels of cortisol and mild depression symptoms were up to eight times more likely to suffer clinical depression later in life.
Teen boys showed an even bigger risk. They were 14 times more likely to be depressed.
Most mental health disorders begin showing signs before someone is 24 years old, and about 1 in 6 people suffer from clinical depression during their lives.
So far, there is no biological test to spot depression.