In the field of peace psychology, violence is categorized as direct or structural; direct violence refers to the interpersonal conflict that harms individuals, while structural violence is expressed through political and economic processes and oppression within a society. Both can have a toxic effect on human health. The causes of direct violence may be associated with physiological processes of development and may be informed by neurobiology. Contextual causes of direct violence include economic poverty, social discrimination and crowding as well as violent acts being condoned or left unaddressed by the family, community or state. The root causes of structural violence include systematic deprivation, unfair political systems and powerful, inequitable social hierarchies.