An MRI scan of the brain. Image via Helmut Januschka

Our understanding and awareness of depression has, thankfully, evolved some way beyond the old-fashioned, “Pull yourself together” response. Most now know that it’s a multi-faceted, shape-shifting, and frequently debilitating condition that transcends race, sex, and creed. But we still don’t know exactly why some become depressed and some don’t.

We know that people may be genetically predisposed to depression and anxiety disorders. We also know that specific life events may trigger depressive episodes in those who have previously been the picture of mental health. But so far we’ve been unable to identify one single, definitive catalyst. However, new research suggests that, for some people, depression may be caused by something as simple as an allergic reaction. A reaction to inflammation—a product of the body, not the mind.

George Slavich, a clinical psychologist at the University of California in Los Angeles, is one of an increasing number of scientists who believe we need to be looking at our physiology to better understand […]