When faced with threats to physical or psychological well-being, our bodies and brains respond in a variety of self-protective ways, including the production of stress hormones adrenaline and cortisol. Our ability to turn this response on and off is critical to healthy functioning in society, and scientists now believe that significant adversity--and the lack of a supportive environment of relationships--in early childhood can trigger lifelong problems regulating this stress system. A nurturing, supportive environment may be the best protection a child can have against the harmful effects of stress in early life. Studies prove that it's easier and less expensive for society to provide what's needed in early childhood than to remediate for the aftereffects later in life. Scientists note four key areas in which policies and scientific knowledge are at greatest variance: starting before birth; confronting child abuse and neglect; ensuring the best possible child care; and addressing depression and other mental-health challenges.