The traumatic events in the Boston area in the past week affect people in different ways.
Survivors and witnesses might face life-time scars.
Another group of people are also vulnerable: Refugees from violent trouble-spots around the world now living in the Boston area.
"It's only been a few days, but we're already seeing some people who've been deeply affected," says Alexandra Weber, director of behavioral health at one of the main refugee assistance agencies in Boston, the International Institute of New England.
"Most of the people that we serve, they're coming to the US in order to re-build their lives in safety," says Weber. "And often they're coming because their lives have not been safe in other countries."
"So a bombing of this type," she adds, "at a point in their lives where they feel like they've left those experiences behind, can really re-trigger the emotional response, and the stress response they've had in the past."