Soldiers returning home from combat may be at a heightened risk for developing post-traumatic stress disorder if public support for a war effort is low, according to recent research. Social validation or invalidation shapes the level of distress soldiers feel from the act of killing, the researchers say. The study involved two experiments that asked participants to exterminate woodlice in a modified coffee grinder – in one, having an actor show either interest or disgust for the act and in another, asking participants to record who agreed to the extermination and who refused. In both cases, the conditions that socially invalidated the killing of the bugs led to more distress and guilt among the participants. Ironically, the researchers report in Personality and Social Psychology Bulletin, the very anti-war protests meant to show support for troops but disdain for combat may increase the likelihood that returning soldiers experience mental distress.