Bullying emerges from a tangle of personality traits, brain wiring, hormonal influences, childhood experiences, and social environments, with no single factor acting alone. Research over the past two decades has moved well beyond the old stereotype of the insecure loner lashing out. The picture that has formed is more unsettling and more interesting: many bullies are socially skilled, strategically motivated, and neurologically distinct in how they process other people’s distress.
The Personality Profile of a Bully
One of the strongest and most consistent findings in the field links bullying to a cluster of personality traits psychologists call the Dark Triad: psychopathy (callousness and lack of remorse), narcissism (grandiosity and entitlement), and Machiavellianism (manipulativeness and cynical disregard for morality). A recent systematic review and meta-analysis of workplace bullying found that all three traits predicted perpetration, with psychopathy showing the strongest correlation, followed by narcissism and then Machiavellianism.1PubMed Central. Dark Triad traits and workplace bullying: a systematic review and meta-analysis of personality, power, and psychosocial safety A separate study looking at individual predictors found that Machiavellianism and psychopathy each independently explained a substantial share of the variation in bullying behavior, and that bullies also tended to score high on extraversion and low on agreeableness.2PubMed Central. Workplace bullies, not their victims, score high on the Dark Triad and Extraversion, and low on Agreeableness and Honesty-Humility That last point is easy to miss: bullies are often outgoing, socially confident people, not withdrawn ones.
Low empathy is another consistent predictor, and researchers have started to distinguish between its two forms. Cognitive empathy is the ability to understand what someone else is thinking or feeling. Affective empathy is the capacity to actually share that feeling, to be moved by someone else’s pain. A longitudinal study of young children found that low affective empathy predicted future bullying perpetration, but so did low cognitive empathy.3JCPP Advances. Cognitive and affective empathy predict young children’s involvement in bullying one year later This matters because the popular idea that bullies “know exactly what they’re doing” and simply don’t care turns out to be only half the story. Some bullies genuinely struggle to read social cues, while others read them perfectly well but feel nothing in response.
Emotion regulation adds another layer. Adolescent bullies frequently have difficulty identifying and managing their own emotions, a trait sometimes called alexithymia. When this is combined with a tendency to interpret ambiguous social situations as hostile, the result is a cognitive loop where the bully perceives threats that aren’t there, becomes angry, and then acts aggressively in what feels to them like self-defense.4PubMed Central. The relationship between difficulties in emotion regulation and alexithymia with anger in male adolescents with bullying behaviors: the mediating role of hostile attribution bias
What Happens Inside a Bully’s Brain
Brain-imaging research has started to reveal what makes a bully’s neural processing different. In one study, adolescents who reported higher levels of bullying showed greater activation in the ventral striatum, amygdala, medial prefrontal cortex, and insula when they watched scenes of someone being socially excluded. Those brain regions are associated with reward processing, salience detection, and motivation.5PubMed Central. Links between adolescent bullying and neural activation to viewing social exclusion In plain terms, while most people’s brains register someone being left out as unpleasant, a bully’s brain may register it as interesting or even rewarding.
The amygdala, which processes emotional reactions to faces, plays a particularly nuanced role. A study of adolescents found that higher amygdala response to angry faces predicted more relational bullying, but only when the amygdala response to fearful faces was low.6Social Cognitive and Affective Neuroscience. Amygdala activity to angry and fearful faces relates to bullying and victimization in adolescents This suggests a selective emotional tuning: the bully’s brain is highly reactive to signs of threat or confrontation but relatively unmoved by signs of distress in others. It is a pattern consistent with the empathy findings above, written in neural circuitry.
Hormones modulate these circuits. Testosterone activates subcortical brain areas that drive aggression, while cortisol and serotonin generally act as brakes on those impulses. When cortisol is low and testosterone is high, the prefrontal cortex has a harder time restraining emotional signals from deeper brain structures.7PubMed Central. Testosterone and Aggressive Behavior in Man This does not mean testosterone “causes” bullying. Most high-testosterone individuals are not bullies. But the hormonal balance between activation and inhibition helps explain why some individuals have a lower threshold for aggression than others.
Genetics and Epigenetics
The question of whether bullying “runs in families” is more complicated than a simple yes or no. A study of over 500 children tracked from first grade into early adulthood used a genetic risk score derived from conduct-disorder research to predict bullying profiles. The score was associated with which type of bully a child became, but the relationship was not straightforward: children in a moderate bully-victim profile had the highest genetic risk scores, while those in a high bully-victim profile had the lowest.8Psychiatry Research. Evaluating the genetic susceptibility to peer reported bullying behaviors Genetic predisposition, in other words, shapes the terrain but doesn’t draw the map.
Epigenetics offers a more dynamic view. Adverse early experiences can alter how genes are expressed without changing the DNA sequence itself, and these changes can persist into adulthood. Research has linked early-life adversity and aggressive behavior to altered DNA methylation patterns across the genome, particularly in genes involved in the serotonin system, stress response, and dopamine signaling.9eScholarship@McGill. The methylome of early adversity and aggression10PubMed. Epigenetics of Aggression This means a child who grows up in a harsh or unpredictable environment may undergo biological changes that make aggressive behavior more likely, creating a bridge between the social environment and the neural mechanisms described above.
How Parenting and Home Life Shape the Behavior
Parenting style is one of the most studied environmental predictors. A large study of over 8,700 Chinese adolescents found that parenting marked by both high expectations and high warmth significantly reduced bullying behavior. The mechanism was not just direct discipline; this style of parenting improved the child’s interpersonal awareness, their ability to read and respond to social situations, which in turn reduced the impulse to bully.11PubMed Central. The effect of parenting styles on adolescent bullying behaviours in China: The mechanism of interpersonal intelligence and intrapersonal intelligence Conversely, parenting that was either highly authoritarian with little warmth, or permissive with few boundaries, predicted more bullying.
This finding aligns well with what we know about emotion regulation. Children who never learn to name their feelings or to see things from someone else’s perspective are working with a smaller emotional toolkit. When conflict arises, they reach for the bluntest tool available. Hostile home environments also feed the hostile attribution bias described earlier: a child who grows up expecting aggression learns to see it everywhere, even where it doesn’t exist.
The School Environment Matters More Than You Might Think
Individual psychology only goes so far. The same child who bullies in one school might not in another, because institutional climate has a measurable effect on bullying rates. Schools with stronger engagement, clearer safety protocols, and better teacher-student and parent-teacher relationships see more bystander defending and less passive tolerance of bullying. These effects were especially pronounced for Black and Latino youth, highlighting how relational trust within a school can serve as a buffer.12PubMed Central. School Climate and Bullying Bystander Responses in Middle and High School
The transition between schools, particularly from primary to middle school, is a high-risk window. A longitudinal study in Portugal found that students who perceived improving teacher-student relationships, peer relationships, school safety, and fairness of rules across that transition showed declining victimization and bullying. Boys showed a larger increase in victimization during the transition than girls did.13Contemporary Educational Psychology. The influence of school climate in bullying and victimization behaviors during middle school transition The implication is that bullying is not just about who a child is; it’s also about what the surrounding institution permits and inadvertently encourages.
Bullying as Social Strategy
One of the more uncomfortable findings in this literature is that bullying often works, at least in the short term. A meta-analysis of studies on bullying and peer status found that bullying predicted higher popularity among peers over time. Bullies were also more likely to be rejected by some peers, but the popularity gains remained statistically significant even after adjusting for confounders.14PubMed Central. Bullying perpetration and social status in the peer group: A meta‐analysis In other words, bullies gain visibility and social dominance while simultaneously being disliked by a segment of the group. They trade broad acceptance for power.
Evolutionary researchers argue this is not accidental. A recent analysis found that bullying was positively associated with social dominance and dating popularity, but these advantages depended on the bully also using manipulative affiliation, essentially switching between coercive and prosocial strategies depending on the audience.15PubMed. An Evolutionary Perspective on Bullying and Social Power: The Roles of Cooperation and Manipulation The picture that emerges is of bullying as a flexible social tool rather than a mindless expression of rage. The most effective bullies are not the ones who are aggressive all the time; they are the ones who know when to be aggressive and when to be charming.
This strategic dimension also shows up across species. A large cross-species analysis of dominance hierarchies in 172 social groups spanning 85 species found that while most groups followed a simple downward heuristic (aggress against anyone lower-ranked), roughly a fifth showed a pattern the researchers specifically labeled “bullying,” where aggression was directed at individuals ranked far below the aggressor.16Proceedings of the National Academy of Sciences. Aggression heuristics underlie animal dominance hierarchies and provide evidence of group-level social information Bullying in this context was associated with more sophisticated use of social information. It was not the primitive strategy; it was the calculated one.
Gender Differences in How Bullying Shows Up
Boys and girls bully differently, and the differences are more structural than many people assume. A study examining the factor structure of bullying behavior found that boys’ bullying encompassed both physical and relational forms, while girls’ bullying was predominantly relational, focused on social exclusion, rumor-spreading, and alliance manipulation. Girls also showed greater longitudinal stability in their bullying patterns and stronger pathways from being victimized to later becoming perpetrators.17International Journal of Educational Research. Does the conception of bullying differ by gender? Examining differences in factor structures, longitudinal stabilities, and victimization-perpetration overlap
The personality correlates differ by gender as well. In men, higher physical aggression is linked to lower agreeableness and lower extraversion. In women, higher physical aggression is associated with more depression and lower stress management. Relational aggression, however, is tied to low agreeableness in both sexes, though men who are relationally aggressive tend toward neuroticism while women who are relationally aggressive tend toward lower interpersonal skills.18Social Behavior and Personality: an international journal. GENDER DIFFERENCES IN RELATIONAL AND PHYSICAL AGGRESSION These findings suggest that the “same” behavior, relational aggression, may have different psychological roots depending on who is doing it.
The Bully-Victim
Not all bullies fit neatly into a single category. A significant subset of aggressive children are also being bullied themselves, a group researchers call bully-victims. A study of African American children found that emotion dysregulation and anxiety symptoms were predicted by an interaction between bullying and victimization. For children low in victimization, higher levels of bullying predicted more emotional problems. But for children who were heavily victimized themselves, bullying did not additionally predict these outcomes, possibly because the distress of being victimized was already so high that perpetrating aggression did not add measurably to it.19Journal of Black Psychology. Emotion Correlates of Bullies, Victims, and Bully-Victims in African American Children
Bully-victims tend to have worse outcomes than either “pure” bullies or “pure” victims. They often come from the most chaotic home environments, have the poorest social skills, and face the most intense peer rejection. Understanding this subgroup matters because interventions that treat all bullies the same may miss the fact that some aggressive children are also deeply distressed and need a different kind of support.
Cyberbullying and the Disinhibition Effect
The shift to online environments has changed the calculus of bullying in ways that extend beyond simply giving bullies a new platform. A systematic review of online disinhibition and adolescent cyberbullying found that greater feelings of disinhibition online corresponded with a higher likelihood of cyberbullying. The mechanism worked partly through moral disengagement, the ability to rationalize harmful behavior as acceptable, and through lower self-control.20ScienceDirect. Online disinhibition and adolescent cyberbullying: A systematic review The evidence on anonymity specifically was more mixed, with inconsistent results across studies. The more reliable driver seems to be the broader psychological experience of feeling “freed” from normal social constraints online, not anonymity alone.
This has practical implications. Removing anonymity, a common policy proposal, may not be sufficient to curb cyberbullying if the disinhibition effect is driven more by the absence of face-to-face social cues than by whether a user’s name is visible. The same personality traits that predict in-person bullying, particularly the Dark Triad combination, likely predict cyberbullying as well, but the online environment lowers the threshold for people who might never bully face to face.
What Happens to Bullies Later
The long-term health trajectory of bullies contains one of the field’s stranger findings. A prospective study tracking participants from childhood into adulthood measured C-reactive protein, a marker of systemic inflammation associated with cardiovascular disease and other chronic conditions. While CRP rose for all participants over time, being bullied predicted steeper increases. Being the bully, by contrast, predicted lower increases in CRP than uninvolved children, even after controlling for body weight, substance use, and mental health.21PubMed Central. Childhood bullying involvement predicts low-grade systemic inflammation into adulthood The researchers suggested that bullying may confer a kind of biological “protection” through enhanced social status, though they were careful not to frame this as a health recommendation.
In workplace settings, bullying continues to exact a toll on targets. Workplace bullying has been linked to reduced life satisfaction and greater functional impairment among those on the receiving end, with these factors mediating the pathway to emotional distress.22PubMed Central. The Impact of Workplace Bullying and Organizational Incivility on Nurses’ Emotional Distress For the perpetrators themselves, the picture is more ambiguous. The same personality traits that drive workplace bullying, particularly Machiavellianism and psychopathy, are often associated with career advancement in competitive organizational cultures, which may partially explain why workplace bullying remains so persistent despite decades of awareness campaigns.
Prevention Programs and What They Change
If bullying arises from such a complex mix of biology, personality, and environment, can school-based programs actually reduce it? The evidence suggests yes, with caveats. The KiVa antibullying program, developed in Finland, is one of the most rigorously evaluated. A large randomized controlled trial in the Netherlands found that both victimization and bullying decreased in KiVa schools compared to control schools, though it took two full school years of implementation before the effects became clearly significant.23PubMed Central. A Large-Scale Replication of the Effectiveness of the KiVa Antibullying Program: a Randomized Controlled Trial in the Netherlands
The program works partly by changing bystander behavior. KiVa increases students’ sense of responsibility to intervene and their expectation that intervening will actually stop the bullying.24Journal of School Psychology. Effects of the KiVa anti-bullying program on defending behavior: Investigating individual-level mechanisms of change This is a fundamentally different approach from targeting the bully directly. Instead of trying to change the personality of the child doing the bullying, it changes the social environment that rewards or tolerates the behavior. When bystanders shift from passive witnesses to active defenders, the social payoff of bullying collapses.
The results are not universal, though. A three-arm trial of KiVa in Chile found only a small effect on victimization and witnessed bullying, and no significant effect on bullying perpetration itself.25PubMed. Effectiveness of the KiVa Antibullying Program with and without the Online Game in Chile Cultural context clearly matters. A program designed for Nordic schools does not automatically transfer to a different social and educational system. The underlying principle, that shifting peer norms and bystander expectations can reduce bullying, appears sound, but the specific implementation has to fit the local culture.
When the Label Gets Applied Too Broadly
One risk in the growing public conversation about bullying is that the term has started to expand beyond its original meaning. Researchers define bullying as repeated aggressive behavior involving a power imbalance. A single argument between equals, a rude comment from a stranger, or a personality clash between coworkers does not meet that definition. When “bullying” gets applied to every interpersonal conflict, it dilutes the seriousness of the real thing and makes it harder to design interventions that target the actual mechanism: the strategic, repeated exploitation of a power differential by someone with a specific psychological profile.
The research reviewed here paints a picture of bullying as a behavior with identifiable biological precursors, measurable brain-level differences, consistent personality correlates, and environmental triggers that can be modified. None of these factors is destiny on its own. A child with high genetic risk, a reactive amygdala, and a difficult temperament who grows up in a warm, structured home and attends a school with a strong antibullying culture may never bully anyone. A child with none of those biological risk factors who lands in a chaotic home and a permissive school environment might. The factors interact, and the interaction is where the real story lives.