Psychological stress may be deadly. Feeling lonely, depressed or socially rejected sets off alarm bells in the brain similar to those from a physical injury hurt and triggers activity in genes linked to inflammation. Inflammation is related to a number of serious diseases including cancer, heart disease and depression.

“It is clear that our emotional state is intimately linked to our physical health,” said Steven Cole, an associate professor of medicine at the University of California, Los Angeles, who was not involved in the study. “However, it is less clear how all the components work together to influence our physical well-being.”