Affective disorders (ADs) are highly prevalent disorders all over the world. Over 163 million people had major depressive disorder (MDD) in 2017 (1). In 2019, an estimated 280 million individuals worldwide were affected by depression, while approximately 40 million were diagnosed with bipolar disorder (BD) (2). MDD and BD are serious ADs that negatively impact normal and social life. Given the high prevalence and psychiatric severity, the associated suicide risk poses a serious public health concern. At the same time, the pathogenesis of each disorder involves multiple factors and complex pathological mechanisms that remain unclear.

Suicide is a severe outcome of ADs, including ideation, attempt, and completion. Completed suicide is defined as an intentional self-directed injurious act with the goal of self-imposed fatality. A suicide attempt is a nonfatal act driven by the intent to die. Whether suicide is only attempted or completed, each is preceded by suicidal ideation, that is, thinking about or planning death. Suicidal ideation is a strong predictor of suicide attempts and completed suicides (3).

Both BD and MDD are associated with a high risk of suicide. For example, a study reported that approximately 30% of BD patients attempt suicide at least once in their lifetime (4). Another study found that approximately 20% of patients with first-episode MDD in youth attempted suicide (5). According to Miola et al. (6), type II BD carries a greater suicide risk than MDD. Furthermore, patients with recurrent depression and those in the early stage of a major depressive episode are at an increased risk of suicidal behavior (7). However, another study found that in 87 patients with ADs, suicide attempts were more severe in the later course of the illness. Notably, the risk of suicide among adolescent MDD patients has been increasing annually (8). The high rate of suicide among patients with ADs calls for greater awareness and intervention from clinicians.

Beyond ADs, additional predictors of suicide include genetic factors, personality traits, gender, quality of social network, personal and interpersonal difficulties, and stressful life events (9–12). Personality characteristics have considerable influence on the emergence of suicidal behavior (10, 13). Eysenck’s personality theory classifies personality traits as neuroticism, extraversion, and psychoticism. The Eysenck Personality Questionnaire (EPQ) is a self-reported questionnaire grounded in Eysenck’s personality theory. In the EPQ, the neuroticism score reflects levels of anxiety, depression, and self-doubt. The score for psychoticism indicates the degree of egocentricity, impulsivity, hostility, and antisocial behavior. The extraversion scale measures a continuum from introversion to extraversion, incorporating classical temperament types: phlegmatic (introverted-stable), melancholic (introverted-unstable), sanguine (extraverted-stable), and choleric (extraverted-unstable) (14).

Brezo et al. (15) reported that neuroticism scores may serve as indicators of suicidal risk. Neuroticism increases the risk of suicide in both general populations and individuals with ADs, and remains a significant predictor among women with ADs (16). Lower emotional stability, reflected by high neuroticism, is associated with rumination and depressive symptoms, both of which are strongly linked to increased suicide risk (17). This finding aligns with the results of Bi et al. (18), indicating that higher neuroticism increases the risk of suicide attempts among individuals with psychiatric disorders. Individuals with elevated neuroticism are more sensitive to negative emotions and stress, which may exacerbate depressive symptoms and contribute to increased risk of suicide. In MDD, neuroticism may worsen mental health by aggravating core depressive symptoms, including concentration difficulties and fatigue (19).Research indicates that patients with chronic MDD exhibit elevated risk of suicide and higher neuroticism scores (20).

Compared to MDD, the link between neuroticism and suicide risk in BD is more complex, as neuroticism remains a stable trait that persists even during remission (21). High neuroticism is associated with poor emotional regulation and heightened susceptibility to depressive episodes. In BD, it is also linked to cognitive impairments, including difficulties with decision-making, category fluency, and response inhibition. These deficits impair social functioning and contribute to elevated risk of suicide. In BD, high neuroticism is associated with suicidal ideation in the absence of prior suicidal behavior, and is linked to increased risk of new-onset suicidal tendencies (22). A previous study (23) reported that BD episodes with mixed features, particularly agitation, tend to result in suicidal behaviors. This susceptibility contributes to elevated rates of suicidal ideation and behaviors during major depression or mixed episodes (24). However, evidence linking neuroticism to suicide risk in BD is limited and less conclusive than in MDD. Negative urgency, a facet of impulsivity, has been linked to both suicidal ideation and neuroticism in BD, but its neural basis remains unclear (25). In a longitudinal study, Kamali et al. (26) found that baseline personality traits did not predict suicide attempts in BD. However, neuroticism emerged as a predictor of suicidal ideation over the course of illness.

In summary, neuroticism, which is linked to both depressive symptoms and suicide risk, contributes to the elevated suicide risk observed in individuals with MDD or BD. However, how neuroticism specifically influences suicide risk in MDD and BD remains unclear. This study aimed to explore the relationship between neuroticism and suicide risk by examining the mediating role of depressive symptoms. It further examined how neuroticism and depressive symptoms interact in both lifetime and current suicide risk, with the goal of generating clinically relevant insights for targeted intervention and prognosis.

This study examined the role of personality traits, particularly neuroticism, in the risk of suicide among patients with ADs, based on qualitative information concerning suicide risk, the suicide item of HAMD-17, and the EPQ. Across multiple analyses, neuroticism demonstrated a consistent association with suicide risk. Neuroticism showed a significant association with both lifetime and current suicide risk in patients with ADs. In univariate analyses, lifetime suicide risk was significantly associated with neuroticism; however, this effect was no longer significant after controlling for covariates. Mediation analyses showed that the effect of neuroticism on current suicide risk was mediated by depressive symptoms. In MDD patients, neuroticism contributed to an increased current suicide risk. The findings underscore neuroticism as a significant driver of suicide risk, both indirectly through depressive symptoms and directly. This effect is most pronounced in the context of heightened depressive symptoms.

Personality traits are unique and inherent to everyone and influence emotions, judgment, decisions, and behavior. According to Eysenck’s theory of personality, neuroticism is a stable personality trait (14). Thus, a high EPQ-N score suggests a persistent tendency experience a range of negative emotional states, including anxiety, frustration, envy, hopelessness, and loneliness, compared to individuals with a low score. The present study extends prior findings on the association between neuroticism and suicide risk, by clarifying its differential influences in MDD and BD.

Neuroticism, as measured by the EPQ-N, was elevated in participants with ADs who reported both lifetime and current risk of suicide. Patients with ADs and high EPQ-N scores were more likely to report lifetime suicide risk. A retrospective cohort study reported that high levels of neuroticism in adolescents with ADs may increase the risk of suicide in adulthood by promoting maladaptive behaviors (35). Su et al. suggested that a high level of neuroticism was an independent risk factor for both suicidal ideation and attempt. In addition, the combination of elevated neuroticism and reduced extraversion may characterize a subgroup of patients at particularly high risk for suicide (36). Another study identified neuroticism as a potential marker of chronic suicide risk (37). This study builds on previous findings by further clarifying the contribution of neuroticism to lifetime suicide risk in patients with ADs. Neuroticism predicted suicide risk in univariate analyses, but this effect was attenuated after controlling for factors such as living alone and prolonged illness. This supports the stress-vulnerability hypothesis (38), suggesting that neuroticism, as a biological vulnerability, plays a stronger role under high-stress conditions and a diminished role when stressors are minimal.

This study further showed that, among patients with MDD, high EPQ-N scores were significantly associated with current suicide risk. This result is consistent with previous studies (10, 39). Acute episodes of MDD are typically characterized by persistent low mood, lack of pleasure and interest, sleep and appetite disturbances, low energy, feelings of worthlessness, and, in severe cases, cognitive dysfunction, including memory deficits (40–42). Severe or persistent MDD may impair patients’ social functioning (43–45), leading to increased social isolation and heightened suicide risk. This cross-sectional study identified neuroticism as a contributor to current suicide risk, partly through depressive symptoms. The severity of depressive symptoms was evaluated in accordance with each participant’s clinical status at the time of assessment, encompassing both acute depressive episodes and remission. These observations indicate that the impact of neuroticism on current suicide risk is not restricted to periods of active depressive symptomatology. Rather, its influence appears to extend across various stages of illness. These findings support the view that neuroticism is a stable personality trait whose influence on current suicide risk endures throughout the course of MDD. Furthermore, neuroticism contributes directly to suicide risk and exacerbates depressive symptoms, which in turn further increase suicide risk in patients with MDD. According to the mediator-moderator model (46), neuroticism influences suicide risk by affecting depressive symptoms. As a mediator, depressive symptoms help explain the relationship between external stressors and internal personality traits. For example, individuals with high neuroticism tend to experience worsening depressive symptoms under stress or negative events, often accompanied by persistent difficulties in emotion regulation and ineffective coping strategies. This pattern of cognitive distortion, including over-interpretation and catastrophizing, further amplifies suicide risk in these patients.

Elevated neuroticism has also been identified as a predictor of BD symptoms, in both one-dimensional models (bipolarity) and two-dimensional models (mania and depression) (47). Although the suicide rate is high in BD, most cases occur during depressive or mixed episodes (48), underscoring the contribution of depressive symptoms to suicide risk in this population. One key finding of this study is that neuroticism indirectly increases suicide risk by exacerbating depressive symptoms, offering new insight into the suicide risk model in BD. The impact of neuroticism in BD may change over time. In particular, manic and depressive episodes could further shape its influence. Future research should further investigate how neuroticism interacts with clinical features, such as depressive episodes.

This study supports earlier findings regarding the relationship between selected psychological factors and suicide risk. In patients with MDD, disease duration was significantly longer in those with a reported lifetime risk of suicide compared to those without. Studies have revealed that even during remission, patients with chronic depression remain vulnerable to relapse and suicide, particularly as illness duration increases (49). Similarly, Pan et al. (50) found that the high risk of suicidal thoughts and behaviors was associated with the duration of the illness. One possible explanation is that the longer course of illness contributes a decline in social functioning and self-worth, which may, in turn, increase suicidal ideation. This study found that age was significantly associated with current suicide risk. Melhem et al. described that younger patient with depressive symptoms had a higher risk of suicide (51). However, Grav et al. (52) stated that older patients were more likely to exhibit suicidal behavior—a pattern not observed in the current study. In older adults, suicide risk may be related to bereavement, and living alone (53), whereas in younger individuals, it is more often linked to family conflict and impulsivity (54). Living alone often lacks social support, which significantly contributes to increased suicide risk. Feelings of loneliness, isolation, and hopelessness, intensified by living alone, are key drivers of suicidal ideation and behavior. The lack of social support reinforces these emotions and increases suicide risk (55).

The findings of this study suggest that high neuroticism is associated with heightened suicide risk. Neuroticism contributes to current suicide risk through different mediation pathways in MDD and BD, primarily via depressive symptoms. In MDD, neuroticism is associated with current suicide risk through both direct and indirect pathways. Pharmacological treatment remains the first-line approach for managing depressive symptoms. Nevertheless, additional benefit may be gained by combining medical treatment with personality interventions for individuals with high levels of neuroticism. Resilience training, targeted cognitive-behavioral therapy, and mindfulness may be effective strategies for addressing neuroticism. Integrating standard medical and personality-based interventions may lead to improve emotional regulation and reduce suicide vulnerability. In contrast, managing depressive symptoms should be prioritized in BD patients with high neuroticism to effectively address current suicide risk. This can be achieved through mood stabilization, and the reduction of acute symptoms. Meanwhile, by improving emotional regulation and preventing depressive recurrence, personality-informed interventions may offer protection against current suicide risk. Moving forward, these distinctions may inform the development of targeted suicide prevention strategies adapted to individual risk profiles.

A deeper knowledge of its inherent pathological systems may be obtained from multi-omics approaches. This could help identify individual vulnerability traits. It may also support the development of a robust framework for precise risk prediction and targeted interventions.

This study is subject to several limitations. The cross-sectional design of the study prevented the collection of follow-up data on individual trajectories. In addition, the potential effect of antipsychotics medication on suicide risk could not be evaluated. Such evaluations would require longitudinal studies to better clarify the relationship between neuroticism and suicide risk. The focus of this study was on the association between neuroticism and suicide risk—both lifetime and current, without distinguishing between suicide attempts and suicidal ideation. Analyzing the association between neuroticism and either suicide attempts or suicidal ideation was beyond the scope of this study. Future studies should incorporate multiple follow-up assessments to capture changes in depressive and manic symptoms over time. Additionally, a broader age range was included to improve sample diversity. Despite phenotypic differences in ADs across age groups, including participants aged 16 years and older offers substantial value for research. Future studies should expand the sample size, with particular attention to adolescents and young adults. A final limitation is that all participants were from a Chinese population, potentially restricting the generalizability of the findings. Cultural differences in emotional expression, help-seeking, and attitudes toward suicide could influence the observed associations. Future studies should examine the consistency of these patterns across culturally diverse populations.

This study explored the relationship between neuroticism and suicide risk in MDD and BD. The findings demonstrated a significant association between neuroticism and both lifetime and current suicide risk in patients with ADs. Mediation analyses further indicated the neuroticism contributes current suicide risk, by intensifying depressive symptoms, both directly and indirectly. Clinicians are encouraged to evaluate neuroticism to develop personalized interventions and enhance suicide prevention measures.