Ms Huitson is not alone in having a dysfunction in the brain mistaken for one in the mind. Evidence is accumulating that an array of infections can, in some cases, trigger conditions such as obsessive-compulsive disorder, tics, anxiety, depression and even psychosis. And infections are one small piece of the puzzle. It is increasingly clear that inflammatory disorders and metabolic conditions can also have sizeable effects on mental health, though psychiatrists rarely look for them. All this is symptomatic of large problems in psychiatry.

As the mother of two daughters, ages 12 and 19, Dr. Damour knows first hand that parenting is hard and sometimes scary. And that has been especially true over the last few years, as the mental health of children, particularly teenage girls, has suffered.

But a reassuring thread runs through Dr. Damour’s work: You’ve got this, it seems to say. “Mental health is not about feeling good,” she writes in “The Emotional Lives of Teenagers.” “Instead, it’s about having the right feelings at the right time and being able to manage those feelings effectively.”

It can be hard to get kids to agree to see a psychologist or a psychiatrist. In fact this is a common stumbling block for many parents of teenagers struggling with anything from anxiety to ADHD, depression, or an eating disorder. Adolescents need to want to get better, and be willing to work with someone to make that happen. For treatment to work kids need to buy into it, at least a little.