Why do some people experience more severe depression than others, even when facing similar life challenges?
Many factors contribute, but a new study points to two important ones: how people interpret past traumatic events and whether they tend to think in extremes.
For anyone who has found themselves stuck in a loop of harsh self-judgment or has trouble seeing shades of gray, the findings offer valuable insight into how our past and our thinking patterns may shape mental health.
A new study by Marta Salla and colleagues, published in Psychology and Psychotherapy: Theory, Research and Practice (2025), explores how cumulative trauma and polarised thinking—often described as “black-and-white” thinking (also known as all-or-nothing thinking)—together influence the severity of depression symptoms.
The study found that people who viewed their past traumatic experiences in a strongly negative light and who exhibited high levels of polarised thinking reported more severe symptoms of depression.
Moreover, polarised thinking appeared to act as a bridge between trauma and depression, partially explaining how past distress can shape present emotional struggles.
Depression affects about 5% of adults worldwide and is a leading cause of disability.
Many people with depression have a history of trauma, and increasingly, researchers are exploring how the combination of multiple traumas—what’s known as cumulative trauma—can intensify symptoms.
But it’s not just the events themselves that matter. How people think about and interpret those experiences also plays a critical role.
The research was conducted in Spain and involved 172 patients—most of them women—diagnosed with either Major Depressive Disorder, Dysthymia, or both.
All participants completed standardized assessments, including the Beck Depression Inventory-II to measure depression severity. The researchers also used the Cumulative Trauma Scale to evaluate the number, type, and perceived impact of traumatic events.
To measure polarised thinking, they applied a method called the Repertory Grid Technique, which looks at how individuals describe themselves and others in binary terms, such as “good” versus “bad”.
One key finding was that every participant had experienced at least one traumatic event.
The most common types were “secondary trauma” (such as witnessing a traumatic event) and “survival trauma” (including accidents and life-threatening illnesses).
These events were typically viewed negatively, and this negative appraisal—more than just the occurrence of trauma—was significantly associated with greater depression severity.
Participants who tended to rate people and experiences in extreme terms—using polarised thinking—also reported higher depression scores.
Compared to a general population sample, people with depression showed significantly more black-and-white thinking.
Notably, the researchers found that polarised thinking partly explained the link between trauma and depression: traumatic events with strongly negative interpretations appeared to increase polarised thinking, which in turn was linked to more severe depression symptoms.
This matters because it highlights the potential for cognitive approaches to play a larger role in treating depression, especially when trauma is involved. Addressing not just what happened, but how a person thinks about what happened—and how they think about themselves and others—may be key to recovery.
“Appraisals of trauma, not just the trauma itself, can shape the trajectory of mental health,” the authors noted.
They suggested that therapeutic strategies that target rigid or extreme patterns of thinking could help alleviate symptoms, particularly in individuals with a history of trauma.
The study does have limitations.
Most participants were women, which makes it difficult to assess whether the results apply equally across genders.
The research was also cross-sectional, meaning it looked at a single point in time, so it can’t prove cause and effect. And while the method used to assess thinking patterns was tailored to each individual, the variability in how participants described themselves may influence how comparable the results are.
Still, the study adds to growing evidence that how we process life’s difficulties—especially through our thinking habits—can be just as important as the events themselves. For people living with depression, particularly those who’ve experienced trauma, these findings may offer hope.
They suggest that healing might come not only from working through the past but also from learning to think in more flexible, compassionate ways.
Citation
Salla, M., Aguilera, M., Paz, C., Moya, J., & Feixas, G. (2025). The effect of cumulative trauma and polarised thinking on severity of depressive disorder. Psychology and Psychotherapy: Theory, Research and Practice. Advance online publication. https://doi.org/10.1111/papt.12602
