Traumatic experiences have been shown to have a significant impact upon psychological wellbeing. However, this impact varies between individuals and it appears that certain trauma types and characteristics are more damaging than others. Therefore, developing a better understanding of the specific characteristics responsible for this differential impact would further the field of trauma research and improve interventions for traumagenic mental health difficulties. Moreover, particular negative emotional experiences have also been implicated in the development and maintenance of emotional and psychological distress following traumatic exposure. In particular, negative self-directed emotions, for example, disgust and shame have been shown to play a role across a range of mental health problems. The first section of this thesis describes a systematic literature review that employed narrative synthesis to examine quantitative evidence regarding the differential impact of betrayal trauma level on mental health outcomes. The review’s findings were mixed, however, there was preliminary evidence that high betrayal trauma events lead to more symptom severity than medium or low betrayal traumas. The second section of the thesis is an empirical research paper. The paper reports findings from a study that used mediation analyses to examine the role of self-disgust in the relationship between childhood trauma and psychosis. The analyses also controlled for other relevant self-directed emotions to establish whether there was evidence for the discrete impact of self-disgust over and above related constructs. The study found that self-disgust significantly mediated the relationship between exposure to trauma in childhood and later onset of psychosis. Furthermore, self-disgust mediated this relationship despite the inclusion of self-esteem, external shame and general disgust as covariates. The third section of the thesis is a critical appraisal of the systematic review and empirical study and provides reflections on my experience of the research process as a whole.