In this study, childhood maltreatment increased the risk associated with 9/11 exposure for developing INT and EXT disorders following 9/11. This is consistent with the concept of stress sensitization, which posits that early exposure alters stress response systems such that these systems are primed to respond in ways that increase risk for distress after exposure to later trauma (McLaughlin et al., 2010a; Pratchett and Yehuda, 2011). While the mechanisms by which stress sensitization occurs remains unclear, much evidence suggests that trauma early in life may alter neurobiologic and behavioral systems, thereby influencing subsequent stress responses (Pratchett and Yehuda, 2011). Studies find that childhood adversity is associated with HPA axis dysfunction, that may lead to later development of adult psychopathology (Watson et al. 2007; Newport et al., 2004). Increased behavioral stress reactivity has also been identified among adults who were maltreated as children. For example, individuals with a history of childhood sexual abuse display stronger emotional responses to everyday stressors than those never abused or sexually abused after age 18 (Thakkar and McCanne, 2000). These complex biological and interpersonal systems are
