Childhood Emotional Neglect
Childhood trauma has consistently been identified as a risk factor for PPD, in at least 4 cross-sectional studies and one longitudinal study. The longitudinal study found that childhood emotional neglect, physical neglect, and supervision neglect predicted PPD symptom levels in adolescence and early adulthood . In adolescence, PPD has been cross-sectionally associated with elevated physical abuse in childhood and adolescence, but not sexual abuse . In this study, patients with PPD were also more likely to have PTSD. In a study of psychiatric adult outpatients, PPD was found to associated with both sexual and physical abuse . These relationships were found with other personality disorders as well, and were not specific to PPD. Childhood abuse was also related to PPD symptom level, suggesting a dose-response relationship, even when PPD symptoms were subthreshold for the diagnosis  . Although these studies have focused on chronic trauma from caregivers, acute physical trauma in the form of childhood burn injury has also found to be a risk factor for adult PPD traits .
Brain trauma has been hypothesized to be a risk factor for paranoia . Empirical, cross-sectional research finds that between 8.3 – 26% of brain injury patients meet PPD criteria  . PPD was the second most common PD following TBI . Longitudinal studies in this area are lacking, but are needed to establish the temporal sequence of the association. Another important question regarding the associating with brain injury and PPD is if the relationship is due to neural circuit dysfunction, or if a change in function as result of the injury alters social interactions. As an example of this, persons who are hard of hearing are more likely to develop paranoia, likely through increased difficulty with and stress from communication with others .