Editorial: Resilience and Vulnerability Factors in Response to Stress

Stress exposure is a major determinant for the development of several mental disorders (1), one of the major causes of disability worldwide (2). For both treatment and prevention of mental disorders, the identification of vulnerability and resilience factors is essential. For instance, it is still not clear which factors differentiate between individuals who will develop mental disorders, in particular, post-traumatic stress disorder (PTSD), following exposure to a potentially traumatic event from the ones who will be resilient, i.e., who may show a strong initial reaction to the event but will not suffer long-term mental health consequences and may even go on to develop posttraumatic growth (3, 4). At the moment, the interplay between vulnerability and resilience factors as well as the role of different types of stress in the development of psychopathological conditions remains unclear. Therefore, our research topic aimed to gather scientific contributions on the relationship between stress and psychopathology in general, and in particular on the field of stressrelated resilience and vulnerability.


METHODOLOGICAL ISSUES IN STUDYING VULNERABILITY AND RESILIENCE FACTORS
To investigate vulnerability or resilience factors, prospective longitudinal designs are the methods of choice. However, these designs are costly in time and resources. Alternative designs include longitudinal, retrospective, and cross-sectional studies in victims of traumatic events or longitudinal and cross-sectional studies in so-called vulnerable populations, i.e., in individuals with an increased risk of developing mental disorders, for instance, because they are regularly exposed to stress at work (e.g., nurses in intensive care units) (Favrod et al.; Schäfer et al.), because they have experienced early-life adversity (5,6), or because their parents suffered from a mental disorder, such as depression (7). A further methodological option is to investigate remitted PTSD patients to disentangle the effects of the disorder from potential vulnerabilities. A caveat of this design is, however, that it is not possible to differentiate between chronic, long-term sequelae from the disorder and vulnerability factors present before the onset of the disorder (8).
The majority of the articles published under this research topic report on research performed in vulnerable populations, mostly in individuals exposed to regular stress during work, including nurses

VULNERABILITY AND RESILIENCE FACTORS: WHAT DO WE KNOW? Vulnerability Factors
Vulnerability factors for PTSD can be categorized into pretraumatic, peri-traumatic, and post-traumatic variables. Across all types of potentially traumatic events, variables such as female gender, low socio-economic status, or previous trauma exposure, consistently predict higher PTSD symptom levels. Type of trauma, trauma severity, and the number of traumatic event types a given person has been exposed to are the most important peri-traumatic risk factors. It has to be emphasized, however, that although statistically significant, the weighted effect sizes of all these single variables are very low. One posttraumatic variable sticks out, though, namely, lack of social support post-trauma (9,10).
The authors of our topic have focused, on one hand, on the investigation of cognitive mechanisms involved in the development of PTSD and, on the other hand, on the identification of vulnerability factors specific to the context of the stress experience, extending therefore the state of the research. With regard to cognitive processes, Kleim et al. evidenced in a sample of assault survivors in Switzerland the role of specific linguistic markers, showing that more cognitive elaboration is associated with lower risk for PTSD. Millon et al. reported that autobiographic memories of stressful events are stronger in women with than in women without experience of sexual violence and that the strengths of these memories strongly correlated with traumatic cognitions, ruminative thoughts, and psychopathological scores irrespective of the presence of PTSD. Changes in neural connectivity also differentiated healthy individuals from PTSD and remitted PTSD, suggesting that specific neural functioning could be a vulnerability factor for PTSD (Sun et al.).
Context-specific vulnerability factors were evidenced in traumatized child samples, with Nsabimana et al. reporting that being institutionalized in an orphanage and having at least one living parent is a vulnerability factor for reduced self-esteem and increased externalizing behaviors.

CONCLUSION AND CLINICAL IMPLICATIONS
Our research topic also points out the necessity to develop wellvalidated measures of stress, resilience, and vulnerability, in particular, culturally adapted measures to stimulate research outside of the industrialized countries. Further, none of the presented studies used a prospective longitudinal design in vulnerable individuals, which would be the method of choice to identify vulnerability and resilience factors. This should be the focus of future studies and become a priority for funding agencies.
In addition, this research topic highlights the role of welldocumented resilience factors, including perceived social support and SOC, to mediate the effects of stress on mental health in vulnerable individuals. In addition, mindfulness abilities, successful emotion regulation strategies, and positive affect, among others, were identified as potentially promising protective factors. The identification of resilience and protective factors is in turn relevant for the development of specific clinical prevention and intervention programs. This is well illustrated by the results of a preventive stress prevention program (Ge-D-Stress) in university students that successfully increased quality of life and resilience factors and was able to decrease psychological symptoms as well by activating several psychosocial resources (Recabarren et al.). However, the majority of the published works in this research topic investigated vulnerability factors. Interestingly, they focused on the role of cognitive and neural processes as well as of context-specific factors, for instance, related to the work environment or the cultural context. A better understanding of specific vulnerability factors might allow us to detect individuals at risk in specific populations in order to provide tailored preventive or clinical interventions, such as the Ge-D-Stress program.