Supervised by: Ellen Froustis MA, MSc. Ellen Froustis is a DPhil. Education candidate at the University of Oxford. She has a Master’s of Education-Special Emphasis School Counselling and a Master’s in Clinical Psychology. As the founder and director of EIMAI, and regional director of Peace Jam Greece, Ellen provides youth leadership development programs, bringing together youth with Nobel Peace Laureates and university students to create positive change in themselves and their communities. Ellen has served as General Secretary of the Greek Adlerian Psychological Association (2012-2016) and Vice President of Habitat for Humanity, Greater Athens (2006-2010). Ellen’s work with youth and schools has been awarded by the Near East Council of Overseas Schools, The Loukoumi Make A Difference Foundation, The Nobel Peace Laureate’s Billion Acts of Peace and Character.Org for best practices in character education.


This investigation looked into the causes and treatments for Cluster B and C personality disorders and the differences between the two clusters. Oxford Scholastica Psychology Interns conducted a literature review and summarised the key findings to make a comparison between the two clusters. The strongest environmental factor shared by both Cluster B and C personality disorders was childhood abuse and poor parenting, resulting in trauma. Antisocial-Personality disorder, a cluster B disorder often characterised by violence and aggression, is heavily associated with more severe forms of childhood trauma, especially sexual abuse. From a neurobiological perspective, abusive parenting has the potential to affect the normal growth of the emotional and decision-making parts of the brain in children that must endure the daily distress of abuse in their lives. It was found that both Cluster B and C personality disordered patients have abnormalities in the amygdala – the area of the brain regulating emotion. Abnormalities of the amygdala in Cluster B patients mainly impacts impulsiveness whereas this for Cluster C patients, it impacts predominantly anxiety. As for treatment, both Cluster B and C personality disorders have been mainly treated using cognitive behavioural therapy (CBT) (Beck, 1990). Cluster C disorders respond to treatments better than Cluster B disorders, which are more difficult to treat. Treatments which have been developed specifically for many Cluster B disorders, and particularly for BPD, have found some effectiveness beyond CBT. These are Dialectical Behavioural Therapy (DBT), Schema Therapy, and Mentalization Based Therapy (MBT). Medication cannot effectively treat these disorders beyond the use of SSRIs in treating the comorbidity of anxiety or depression, which often develop as a result of  the distress that the personality disorders cause. Overall, the best preventative measures are associated with family support to prevent child abuse and collective interventions to identify red flags on a school and community level. Interventions to educate and support families are vital regardless of their socioeconomic status, as abuse is prevalent across SES (socioeconomic status), gender and culture.


Personality disorders (PD) make lives more challenging for people diagnosed with one and for the people around them. It is considerably harder to notice or detect if someone is diagnosed with a personality disorder, compared to a physical disorder. In fact, it is difficult for people to accept they have a personality disorder, even after diagnosis. However, in time, their behaviour often gives clues that perhaps their logic is not so normative, and their response to the world is rather extreme, in comparison to others. Personality disorders are characterised in “clusters” according to the Diagnostic Statistical Manual (DSM), which is used by practitioners to diagnose mental illnesses (APA, 2022). Cluster A disorders involve behaviours considered strange or erratic. Cluster B disorders exhibit impulsivity and extreme emotions. Cluster C disorders share the common trait of anxieties and fears. Cluster B and C personality disorders are often harder to detect than the more visible features of Cluster A (APA, 2022). The causes and treatment of a personality disorder can make a significant difference in the disorder’s progression. Prevention and treatment is an important part of research into mental health and therefore, causal factors for Cluster B and C disorders, and differences in treatment will be explored in this research paper.

Cluster B includes four types of personality disorders, which are: Antisocial Personality Disorder (ASPD), Borderline Personality Disorder (BPD), Histrionic Personality Disorder (HPD), and Narcissistic Personality Disorder (NPD). All four of them are characterised by intense experiences of emotions, as well as a tendency to behave impulsively and irrationally (APA, 2022). While Cluster B disorders are generally characterised by dramatic, emotional or erratic behaviours, the disorders can be distinguished in terms of their primary characteristics: ASPD i characterised primarily by a lack of empathy for others, BPD by unstable emotions, relationships, and behaviours, HPD by an excessive need to be in the centre of the attention, and NPD by an exaggerated self-image. Narcissistic Personality Disorder in particular is characterised by constant/exaggerated display of condescending superiority, lack of empathy and concern for others, and intense preoccupation with self-regard/self-esteem (APA, 2022).

Cluster C personality disorders are characterised by anxious, fearful thinking or behaviour. They include; Avoidant Personality Disorder, Dependent Personality Disorder and Obsessive Compulsive Personality Disorder. Personality is defined as the combination of thoughts, emotions and behaviours that makes you unique. It’s the way you view, understand, and relate to the outside world, as well as how you see yourself. Personality disorders in Cluster C, like all others, are thought to be caused by a combination of genetic and environmental influences. Your genes may make you vulnerable to developing a personality disorder, and a life situation may trigger the actual development. Individuals with Avoidant Personality Disorder view themselves as inferior to the people around them. They tend to experience extreme anxiety and low self esteem in social settings. Those with Dependent Personality Disorder believe that they need to rely on others to take care of them. They have trouble making decisions or completing tasks, and need constant reassurance as a result of their lack of self-confidence. Symptoms of Obsessive Compulsive Personality Disorder include hyperfixation to minute details, lack of flexibility, and perfectionism (Massaal-van der Ree et al., 2022).

How common are personality disorders? The prevalence of Cluster C personality disorders exceeds those of Cluster B personality disorders (PD). Cluster C has a prevalence rate of 2.7%, while Cluster B has a prevalence rate of 1.5% (Massaal-van der Ree et al., 2022). However, the majority of research on PDs has focused on Cluster B PDs. Nearly 249.6 million people suffer from these disorders globally. Personality disorders affect a significant minority of individuals. According to most studies, the prevalence of Axis II disorders of the Diagnostic Statistical Manual (DSM) in the general population is around 10 percent. Obsessive Compulsive Personality Disorder (Cluster C) is considered to be the most frequent Axis II disorder in community samples in the United States, followed by Narcissistic and Borderline Personality Disorders (Cluster B). Prevalence rates of personality disorders in other countries (outside of the USA) show wide variation, from 6.1 to 13.4 percent. The averaging of these two low/high percentages results in 9.7 percent (Massaal-van der Ree et al., 2022).

​​It is important that personality disorders are treated because they can significantly disrupt the patients’ lives, as well as those of the people around them. If left untreated, those with personality disorders may face huge difficulties, including: poor interpersonal relationships, difficulty maintaining jobs, and an increased risk of developing poor coping skills such as substance misuse (Pruthi et al., 2016). In the case of ASPD, patients are at a higher risk for engaging in criminal behaviours, which can result in incarceration. Recognising the importance of treatment for personality disorders directly recognises the disruption they cause individuals who are affected by them. By finding solutions in the form of treatment for diagnosed patients, we are able to lessen their day-to-day difficulties and, in the long run, prevent serious consequences, such as resorting to acts of violence, violation of the law, and substance abuse.

As stated earlier, prevalence ratings of cluster B PDs (1.5% of the population) and cluster C PDs (2.7% of the population) show that approximately 249.6 million people globally suffer from these personality disorders alone (Massaal-van der Ree, et al, 2022). People with cluster B and C disorders are often stigmatised, making it harder for them to find their place in society. The topic of personality disorders is important to investigate because of its prevalence in society, and general misunderstandings of the disorders. There are many presumptions and beliefs about personality disorders that are incorrect, and some that have some truth to them. It is important to investigate these disorders so that misunderstandings can be clarified. With the relatively high prevalence of personality disorders in our society, it is important to understand how people with these disorders view and respond to the world, and how we can aid them in their journey to becoming a functioning member of society. 

Oxford Scholastica’s Psychology Intern Co-Researchers will investigate the research question: “What are the causal factors of Cluster B and C personality disorders and differences in treatment?”.

Literature Review

Cluster B Disorders

Borderline Personality Disorder (BPD)

Mental illnesses, including personality disorders, are examined from biological and environmental  perspectives to understand their prevention and to identify targeted interventions. From a biological perspective, genetics can play a big role in defining traits that may be a symptom of a PD. Studies on the neuroanatomy and imaging of Borderline Personality Disorder (BPD) patients showed that abnormalities in the emotional processing areas of the brain (including the amygdala, prefrontal regulatory regions, hippocampus, and others) could explain why people with BPD have difficulty managing impulsivity and emotional outbursts (Pier et al., 2016). According to a literature review written by Pier et al. (2016), BPD was more prevalent in individuals with family members who also have the disorder. A study was conducted to investigate the degree to which BPD clustered within families and how much of this was due to genetic predispositions to BPD. They found that the relative risk for an individual with genetic relations to BPD patients was 3.9.  Furthermore, twin studies have also shown that the heritability of BPD is approximately 40% to 70% (Pier et al., 2016). All of these studies in Pier et al.’s (2016) review contribute to the evidence indicating that BPD is influenced by an individual’s genes.

In an experiment conducted by Völlm et al. (2007), researchers compared the neural responses of cognitive tasks in a control group and a group with Cluster B personality disorders. To test this, they had the participants perform a reward task and a loss task during scanning sessions. They found that during the reward task, there was an absence of prefrontal responses in the patient group, and that the amount of loss of prefrontal response was positively correlated with the patients’ impulsivity scores, such that as impulsivity scores increased, less prefrontal activity was seen. Furthermore, they also found that the orbitofrontal cortex was not activated in the reward task but was activated in the loss task. These findings may be an important factor in the investigation of the causes of Cluster B PDs as another study further backed it up. In a study led by Payer et al. (2015), participants were again, divided into a control group and a group with personality disorders, which was further divided between Cluster B and C. Participants had to undergo image processing of their brains which showed abnormalities in the orbitofrontal cortex. These abnormalities were found to be located at a lower area of the orbitofrontal cortex for Cluster B patients.  People with BPD have shown more activation of the area in the limbic system, which is responsible for processing aggression and fear (Salters-Pedneault, 2020).

The causes of BPD show a strong indication for environmental factors. Environmental causes include: experiences of abandonment;emotional or physical neglect; insensitivity of parents towards a child; and experience of physical or sexual abuse (Salters-Pedneault, 2020). In a study conducted by Kaur and Sanches (2022), environmental factors such as parenting styles were examined. The study categorised BPD by emotional dysregulation, impulsivity, self-harm, an unstable sense of identity, and difficulty maintaining interpersonal relationships. Findings from the study indicated that there was a strong association between parenting styles and a child’s likelihood of developing BPD. Researchers explored categories of parenting styles defined by Baumrind as authoritarian, authoritative, and permissive (Kaur & Saches, 2022). Self-reports of children’s experiences of the different parenting styles indicated that adolescents with BPD received significantly less emotional warmth, more rejection, or overprotection from their mothers in comparison to the control group (Kaur & Sanches, 2022). Furthermore, the study found that childhood trauma predicts insecure attachment, which in turn increases the likelihood of individuals developing BPD. This suggests that childhood trauma and authoritarian parenting styles increase the risk of developing BPD.

The study also explores the possibility of an overlap of family environment and inheritance factors in the development of BPD. Notably, the study also found that there is a  4- to 20-fold increase in the risk of developing BPD when one has first-degree relatives with BPD (Kaur & Sanches, 2022), which suggests that BPD could be inherited. However, an alternative explanation is that the child’s increased likelihood of developing BPD can be due to the influence the home environment has on the child. This is supported by the study’s finding that children with mothers who have a history of trauma  depression (which are often seen in BPD patients) may be at a higher risk of developing an insecure attachment style (Kaur, 2022). As the majority of children spend more time around their mother during early stages of their life, this supports the theory that the increased likelihood of developing BPD when relatives have the disorder is due to the quality of the child’s nurturing in the home environment. 

Furthermore, in a year-long longitudinal study of BPD outpatients, more family involvement was associated with a decreased rate of re-hospitalization, and better recovery. This further supports assumptions that a warm and nurturing home environment can decrease the risk of developing BPD, while also decreasing relapse of BPD. However, the study equally found that family criticism had little influence in the rate of re-hospitalization and recovery of BPD in  outpatients, suggesting perhaps that other environmental or biological factors may be contributing factors.

Finally, the study also found that there are “individual characteristics” that help to manage adversity better. This includes personal traits such as higher intelligence, better self-regulation skills, high self-esteem, and adequate prosocial skills. Environmental factors such as positive family support and parental warmth also contribute to resilience. This suggests that children with a more supportive home environment, as well as certain individual traits, could possibly act as ‘protective’ factors for BPD. Similarly, this also suggests that lack of resilience should be considered as a contributing factor to BPD with a need for further research (Kaur & Sanches, 2022).

Antisocial Personality Disorder (ASPD)

A second Cluster B disorder, Antisocial Personality Disorder, is characterised by interpersonal distress and behaviours that harm others, which can range from mild to criminal (Farrington, 1993; Moran, 1999). It is widely speculated that environmental causes such as abuse and early adverse experiences play a tremendous role in how the brain develops, which for some people, results in an ASPD (Farrington, 1993). Neuroimaging technology is often used to understand the neurobiology of ASPD. Studies show that ASPD is associated with neurobiological, neurodevelopmental and neuropsychological deficits (Bazanis et al., 2002), brain lobe abnormalities in terms of structure (specifically in the left hemisphere) (Raine et al., 2000), aberrant serotonergic function (Dolan et al., 2001) and increased genetic liability (McGuffin and Thapar, 1993). Studies that have been conducted on changes of behaviour due to brain injury indicate that prefrontal damage, specifically in the ventromedial cortex, can be a causative factor for increased impulsivity and poor behavioural control – characteristics similar to those of ASPD (Damasio et al., 1990, 1994). Moreover, patients with antisocial personality disorder exhibit a plethora of prefrontal executive and temporal memory function deficits (Bazanis et al., 2002). Furthermore, studies using fMRI (functional magnetic resonance imaging) scans to detect brain activation have shown that different neural networks are activated to inhibit prepotent responses in people with ASPD compared to people that haven’t been diagnosed with a personality disorder. More widespread temporal and prefrontal areas of the brain are activated in ASPD controls than healthy controls. 

A meta-analysis conducted by Loomans et al. (2010) examined studies conducted between 1990-2009 that used brain scans to investigate ASPD. Findings showed impairments in the prefrontal cortex, amygdala, hippocampus, superior temporal gyrus, corpus callosum and anterior cingulate cortex. These impairments could potentially be the explanation for the antisocial behaviour as there is a high proportion of research supporting these findings. The research also proposed that psychopathy is connected mainly with impairments in a prefrontal-temporal-limbic system. The researchers concluded that detached communication between parts of the brain structure and deficient development of parts of the brain might be the factors contributing to and explanations for the antisocial behaviour of people with ASPD. People with ASPD often carry narcissistic traits.

The causes of  ASPD can be correlated with a myriad of environmental factors that can be divided into two main categories: abuse, and previous mental disorders individuals with ASPD were diagnosed with. Notably, in DeLisi et al., (2019), a mixed measures design was used to investigate the relationship between types of childhood abuse and the occurrence of ASPD. The measures used included interviews with active correctional criminals, and examination of individual case reports (which included documents relevant to the participants’ social and criminal histories as well as their psychiatric and treatment reports). The study concluded that “sexual abuse and physical abuse among various forms of maltreatment are more strongly linked to aggressive forms of deviance” (DeLisi et al., 2019). This suggests that there is a strong correlation between childhood abuse, particularly sexual and physical abuse, and increased likelihood of developing ASPD. 

Furthermore, the study investigated the correlation between other mental disorders that the individuals were diagnosed with and their likelihood of developing ASPD. Oppositional Defiant Disorder (ODD) and  Attention Deficit Hyperactivity Disorder (ADHD) were not significantly associated with the development of ASPD (DeLisi et al., 2019). However, there was a greater risk of ASPD for those with childhood psychopathy, substance use and criminal behaviour (DeLisi et al., 2019). This was supported by the secondary data from participants’ psychiatric diagnoses.  

People suffering from ASPD often have experienced trauma related to betrayal (Yalch et al., 2021). The study gives insight into how high, medium and low levels of  betrayal trauma are associated with ASPD, using a sample from Amazon’s Mechanical Turk (N = 363) and structural equation modelling to differentiate the levels of betrayal trauma. The research indicated a strong association between trauma and ASPD traits in general, but this relationship depends on the influence of specific forms of trauma on different sexes, as well as the severity of the trauma. The research displays that the consistent predictor for males having ASPD traits is high betrayal trauma, whereas the consistent predictors  for females having ASPD traits are medium and low betrayal trauma.

Narcissistic Personality Disorder (NPD)

As a mental health condition, Narcissistic Personality Disorder (NPD) involves three key elements: (i) self-centred, arrogant thinking and behaviour; (ii) a lack of empathy and consideration for other people; and (iii) an excessive need for admiration. Moreover, those with NPD are intensely defined by fixed distinctive thinking and behavioural patterns, which they engage with irrespective of time and space; they are not only tremendously challenging, arrogant, manipulative, self-centred and condescending, but also particularly resilient to changing their extreme behaviour, overreacting to any criticisms, disagreements (Mitra and Fluyau, 2022).

Narcissism could be classified according to the severity of the dysfunctional self-centred attitude and behaviours. Actually, there are a number of narcissistic traits, which can be either: (i) adaptive (or helpful) narcissism, which signifies the so-called “supportive” features of narcissism – for example, an inflated self-image of high self-sufficiency and self-confidence may result in a positive sense of independency and determination; or (ii) maladaptive (or unhelpful) narcissism, which is categorised as NPD with destructive and vicious traits underpinning an idealised, exaggerated, and overstated image of oneself as well as commitment to manipulate and abuse other people. Based on specific traits, there are five subtypes of narcissism including overt or grandiose narcissism, covert or vulnerable type, communal narcissism, antagonistic narcissism and the malignant form:

  •       Overt or grandiose narcissism refers to an exaggerated unrealistic self-image and high self-esteem, which is expressed in an extroverted, problematic, egotistical, and arrogant form. People with overt/grandiose narcissism tend to consistently overestimate their own emotional intelligence, are confident and assertive, and often try to undo any feelings of inferiority.
  •       Covert or vulnerable narcissism emphasises narcissists who are introverted, extremely sensitive to criticism, and have low self esteem. Inconsistent to the well-known dominant trait, covert narcissists are less likely to overvalue their sensitive capacities. They are passive-aggressive and, even, defensive people.   
  •       Communal narcissism refers to those with NPD, who present as unselfish, altruistic, and even supportive people, who assert for impartiality. Nevertheless, they are strictly interested in their social dominance, superiority and power, which is in fact a result of a lack of empathy, and intolerance of failures and imperfections.
  •       Antagonistic narcissists are usually classified as aggressive and hostile people as they consider social interactions as highly competitive situations with a very clear outcome: “to fail/to lose” and “to win”. This kind of approach generally conflicts with communal narcissists.
  •       Malignant narcissism remains the most controversial type, as well as the most destructive form of personality disorder. People with malignant narcissism are aggressive and sadistic, taking advantage of their paranoid thinking and behaviours, and exhibiting antisocial traits.

NPD is recognized as a complex picture focused on characteristic deficits in six broad areas of functioning: (i). self-concept; (ii) interpersonal relationships; (iii) social adaptation; (iv) ethics, standards and ideals; (v) love and sexuality; and (vi) cognitive style (Akthar, 1982). However, the accurate basis of NPD is still not fully known. NPD remains a trait-based disorder, as it is still seen as a pathological amplification of narcissistic traits (Paris, 2014), with a multifaceted pathobiology, such that there is a pattern of factors supporting the occurrence of NPD in adulthood. In NPD, certain traits are amplified to the point of dysfunction. This process often occurs due to feelings of entitlement, or as the result of a  failure to ground assessment of the self in objective accomplishments (Ronningstam, 2010; Paris, 2014). The development of NPD with either an ego dystonic or ego syntonic nature may be explained by an interplay between the biopsychosocial model and modernity theory, resulting in an expressive, excessive and malfunctioning individualism view. Different clinical theories about narcissism promoted by Kohut (1970) and Kernberg (1976), along with the cultural theory promoted by Lasch (1979), collectively describe the roles of excessive individualistic values, fragile self-concept, fear of commitments, temperamental vulnerability, psychological adversity and a disbalance between individual goals and social attachments (Paris, 2014).

Several factors contribute to NPD development, including: a genetic predisposition (family history or a specific trait profile influence vulnerability to later development of NPD) toward the disorder; personality and temperament traits, particularly aggression, decreased tolerance to distress, and dysfunctional affect adjustment; adverse developmental experiences, such as childhood trauma (including physical, sexual and verbal abuse, as well as childhood rejection), hypersensitivity to textures, noise or light during childhood, and a fragile ego during early childhood; antisocial behaviour, often involving disregarding the rights or safety of others;  and excessive praise, which affirms the belief that a child may have extraordinary abilities. Different cognitive and personality studies have emphasised gender differences in narcissism. However, the neural basis of sex-specific narcissism, including morphometry and functional connectivity analyses, are poorly explored. Gender-related differences in brain structure and resting state functional connectivity which have been related to Narcissistic Personality Disorder rely on differences between externally and internally focused attention. These neural aspects of brain structure and functional connectivity are generally more dynamic and intrinsic in females with higher narcissistic scores (as evaluated by the Narcissistic Personality Inventory self-reported measure of narcissism and self-esteem scale) than in males. This might  indicate that it is a blurring of the boundaries between internal reflection and external perception which primarily underlies the gender differences in NPD , as suggested by Yang (2015).

The diagnosis of NPD classically requires that an individual presents at least 5 of the following characteristics: overinflated or grandiose sense of self-importance; need for excessive admiration; constant thoughts about being more successful, powerful, smart, loved or attractive than others, and willingness to take advantage of others to achieve goals; sense of entitlement; lack of understanding and consideration for other people’s feelings and needs; feelings of superiority and desire to only associate with high-status people; arrogant or snobby behaviours and attitudes; and a need for constant praise and excessive admiration. Narcissists feel special and in control as they drive self-glorifying fantasies of boundless victory, power, success, attractiveness, and ideal love. Aside from their grandiosity and obsessive desire for affirmation, which are correlated with dominant and aggressive behaviours (Yang, 2014), narcissists focus on their own dreams, lack empathy, deny reality, and live in their fantasy world. This is reinforced by distortion and magical thinking to defend their insatiable ego from shame, inner emptiness (Paris, 2014; Yang, 2014).

It is not only challenging to adequately define and identify the aetiology of NPD, but there has also been significant debate regarding the methods for managing this personality disorder. Recent publication has detailed some interesting data regarding the relevance of attachment theory to the conceptualization and treatment of pathological narcissism, as well as the potential for transference-focused psychotherapy to be used as a treatment option for NPD (Diamond, 2020). Susanne Bennett has proposed that the relational context of development and the interpersonal interpretive capacities emerge as a part of the attachment system, and both represent significant factors in explaining the aetiology and treatment of narcissism. Several attachment models and their correlation to adult narcissism have been explored, which has resulted in the conclusion that establishing a “secure base” is mandatory for the clinical management of different narcissistic traits.

Furthermore, in a more recent approach to NPD management, Diamond and Hersh (2020) have investigated and analysed the clinical utility of transference-focused psychotherapy in NPD. Given the benefits of this empirically validated theory in patients with Borderline Personality Disorder, Diamond and Hersh (2020) have modified and adapted the technique for NPD and people with narcissistic traits, such that it focuses on disturbed interpersonal patterns of interacting. Their evidence indicates that this treatment is able to address changes in personality organisation and real-world changes in specific areas, including work and love. The authors have also emphasised the importance of assisting patients with maximum flexibility and self-reflection, in order to address the issues of extreme  mental state fluctuations, which are often seen in individuals with NPD.

To summarise, Narcissistic Personality Disorder remains a complex personality disorder that often occurs along with other personality or affective conditions. The holistic approach towards managing and treating NPD should take into account the aetiology, the classification of NPD subtypes, and complications related to disordered personality, and should involve discussions regarding potential management options currently available.

Overall, as evidenced in the Cluster B disorders, childhood trauma appears to impact brain development, while also hindering the growth of resilient personality traits. These changes may  result in individuals having a greater risk of developing personality disorders later in life. This is shown through a study by Back et al. (2021), who tested for PTSD in individuals who had already been diagnosed with personality disorders. They found that childhood trauma has some significant effects on the development of personality, which could cause maladaptive traits (underdeveloped or overdeveloped personality traits) which are often seen in a range of personality disorders.


Cluster C Disorders

Cluster C personality disorders are characterised by anxious, fearful thinking or behaviour. They include; Avoidant Personality Disorder, Dependent Personality Disorder and Obsessive Compulsive Personality Disorder.

Avoidant Personality Disorder (AVPD)

While it is reported that roughly 2.5% of the population meet the criteria  for a diagnosis of Avoidant Personality Disorder, it is believed  to be a disorder which is often undiagnosed and untreated (Smith, 2022). Thus the rate of diagnosis is unlikely to be reflective of the true prevalence of the disorder. It is a chronic disorder that affects both men and women equally. The disorder can develop in childhood, and symptoms have been detected in children as young as 2 years old. However, like other personality disorders, Avoidant Personality Disorder is typically only diagnosed in adults (Smith, 2022).

People with Avoidant Personality Disorder display a number of behaviours that are abnormal and atypical. People with this disorder have a poor self-image, seeing themselves as inadequate and inferior to others. They tend to have a few close friends due to the need to be certain that they will be liked; they also exaggerate problems and have an inability to form stable relationships. People with this disorder also tend to be shy, self-conscious, and awkward due to the fear of doing something wrong or embarrassing. They are overly sensitive and get hurt when they are criticised, and they also tend to have severe anxiety (Smith, 2022).

The exact cause of Avoidant Personality Disorder is not entirely understood by researchers. However, it is believed and widely accepted that both genetics and environment play a role. It is believed that Avoidant Personality Disorder may be passed down in families through genes but this has not yet been proven. Environmental factors, particularly in childhood, do play an important role.  For example, those with the disorder often report past experiences of parental or peer rejection, which can impact a person’s self-esteem and sense of worth (Johnson et al., 1999). While shyness is normal in young children, for those with Avoidant Personality Disorder, this shyness continues into adolescence and adulthood. This can be the result of decreased self-esteem and lack of a sense of worth following rejection during childhood. 

Early traumatic experiences and childhood neglect are also linked to the development of AVPD. Research suggests that children who see their caregivers as lacking in affection and encouragement and/or experience rejection from them may be at increased risk (Johnson et al., 1999). So, too, are children who experience abuse,  or an overall lower level of care. Verbal, physical, and sexual abuse have been shown to increase one’s risk of developing AVPD at varying levels. Researchers note that a change in appearance due to a physical illness can also influence AVPD (Johnson et al., 1999). In response to these experiences, children may avoid socialising with others as a coping strategy. 

Recent studies have begun to compare and contrast AVPD with similarly diagnosed disorders, and have been able to closely relate it to social anxiety disorder (SAD) (Lampe & Malhi, 2018). Researchers have expressed that “AVPD and SAD were likely one disorder with different subtypes” and that a multidimensional model of social anxiety, or a social anxiety spectrum would help to settle disputes over overlapping diagnosis criteria of the two disorders (Lampe & Malhi, 2018). AVPD was also closely compared with dependent personality disorder (DPD) to properly analyse similar symptoms between the two disorders, such as increased sensitivity to criticism, constant demand for reassurance, and feelings of inadequacy (Lampe & Malhi, 2018). The most agreed-upon conclusion was that “these studies are consistent with the high degree of overlap generally reported between PDs in the DSM, particularly within Clusters” (Lampe & Malhi, 2018).

From a neurobiological perspective, one study recorded a hyperreactive amygdala in response to social reappraisal in individuals with AVPD (Danny et al., 2015). As the amygdala’s primary function is the regulation of emotion, this result reveals that the symptoms of AVPD are fueled by anticipatory anxiety. A follow-up study determined that the volume of grey matter in the right amygdala in AVPD patients was greater when compared with healthy controls, which relates mainly to the prevalence of negative emotions (Danny et al., 2016). Grey matter volume was also positively correlated with patients’ STAI-state anxiety score, further confirming that the symptoms of distress in AVPD are associated with grey matter volume in the amygdala.

Obsessive Compulsive Personality Disorder (OCPD)

OCPD is one of the most common personality disorders, reflecting  “reduced cognitive flexibility and planning ability” (Marincowitz et al., 2021). The prevalence of OCPD has been estimated to range from 2.1 to 7.9 % (Zimmerman, 2022). The factors which are involved in the development of OCPD are thought to be: trauma, childhood attachment types, neurochemical and structural abnormalities, as well as genetic vulnerability (Pinto et al., 2015). Most of the empirical evidence available provides support for disturbed attachment as a primary cause for OCPD (Diedrich et al., 2015). OCPD is also highly inheritable, which highlights the genetic factor of OCPD (Hertler et. al 2016). Childhood neglect can have harmful consequences on the development of a child. Their emotional, social, and cognitive development can be affected. Children who are victims of neglect and physical abuse are more asocial and have withdrawn personalities (Hildyard & Wolfe, 2002). Nordahl and Tore (1997) proposed that faulty parenting plays a part in the development of personality disorders. Parents who are emotionally abusive can cause emotional dysregulation and maladaptive social functioning in their child. This can lead to insecurity in relationships with others. (Bukhari et. al 2018). Gluck (2014) suggests that individuals who are raised in an environment which lacks intimacy, is overly focussed on rigidity and perfectionism, or where they are prevented from expressing their feelings are more likely to experience OCPD in later life (Bukhari et al 2018).

Neurobiologically, neuroimaging of OCPD patients showed spontaneous brain activity throughout the brain. This is likely reflective of OCPD symptoms. These patients also had lower hippocampal and amygdalar volumes compared to healthy control subjects. Some OCPD symptoms may be related to limited availability of dopamine D2/D3 receptors in striatal regions, and to the availability of serotonin transporter the midbrain. The Ser9Gly dopamine D3 receptor (DRD3) polymorphism is associated with heightened rates of OCPD symptoms. Males are more likely to suffer from OCPD than females (Light et. al 2006). There is also a possible genetic correlation, as this disorder is more common in individuals with relatives who have OCPD (Bukhari et. al 2018).

In brief, Cluster C disorders have a similar neurobiological profile. Both environmental and genetic factors contribute to this profile.



Cluster B Disorders

The most effective treatment method for Cluster B disorders is psychotherapy (Meadows-Fernandez, 2018). Cognitive Behavioural Therapy (CBT) is an evidence-based treatment now broadly used for many disorders and mental health issues. It focuses on helping people change unhelpful ways of thinking and behaving. The following psychotherapies are based on CBT and were originally developed for the treatment of Borderline Personality Disorder and now used more broadly for Cluster B disorders.

Psychotherapy tries to understand the thinking processes that create negative emotions and reactions, and then teaches strategies to raise awareness and to deal with difficult moments, particularly in the case of regulating intense emotions. In Cluster B disorders, however, psychotherapy is often a challenging method of treatment, as the process is carried out with a therapist, and those with these types of disorders may find it difficult to establish comfortable relationships with the therapist (Narud et al., 2005). Those with Cluster B disorders may refuse diagnosis or proper treatment, unless under court order or perhaps when it is initiated by a significant relationship.

Despite this, specific types of psychotherapy have been deemed to be effective methods of treatment for Cluster B disorders. Dialectical Behaviour Therapy (DBT) is a clinical treatment, which was developed by Dr. Marsha Linehan in the early 1990s. DBT is used to help people with BPD. DBT has evidenced efficiency in treating BPD, as well as other psychological disorders (May et al., 2016). For example, in a meta-analysis of eleven studies which used DBT to treat BPD, Bloom et al. (2012) found that in most cases, DBT treatment resulted in a decrease in suicidal thoughts, self harm, anxiety and depression.  DBT is similar to CBT, as  both psychotherapeutic approaches place heavy emphasis on emotional regulation, with a goal of curbing impulsivity and emotional outbursts. It differs from CBT in that it also includes techniques on self-acceptance and involves more group work (Mind, n.d.). 

Schema-focused Therapy, which is done either individually or in groups, addresses basic childhood needs that have not been met, such as attachment, needs for safety, acceptance, and love. When needs are inadequately met as a child, people often develop unhealthy ways of interpreting and interacting with the world, thus developing maladaptive early schemas. The goal of Schema-focused Therapy, therefore, is to tackle feelings of shame, emotional neglect, enmeshment and social isolation that result from beliefs of unworthiness due to early neglect and abuse (Salters-Pedneault, 2020).

Patients may also be recommended Mentalisation-based Therapy (MBT).  In MBT, the therapist helps the person understand their internal mental state, by helping them to identify how they are thinking and feeling, and how this relates to others (Daubney & Bateman, 2015). Developing alternative perspectives help the client to reconstruct their image as well as their feelings, which may be extreme. Some patients may also find the application of insights from the understanding of emotions through relationships with their therapists effective, thus following the use of Transference-focused Psychotherapy (Daubney & Bateman, 2015).

With respect to medication, there has yet to be any approved drugs for the treatment of cluster B disorders (Ripoll, 2013). When medication is prescribed, it targets specific symptoms which arise from personality disorders, such as depression, impulsiveness, aggression or anxiety. Medications may consist of antidepressants, antipsychotics or mood-stabilisers. Often, stabilising mood using medications supports people in participating in psychotherapy more effectively.

ASPD, a disorder characterised by impulsivity and aggression is one of the personality disorders that is most difficult to treat. ASPD starts in childhood or early adolescence and is diagnosed as conduct disorder. If a person’s symptoms persist past the age of 18 and into adulthood, it is diagnosed as ASPD. The presentation of symptoms of ASPD is moderated by age. Therefore many older adults do not meet the criteria for diagnosis. The US Food and Drug Administration has not approved any medications for treatment of the disorder and there are no proven psychological treatments. However, medications can be prescribed to treat comorbid disorders (e.g., panic disorder, major depression disorder), or to target aggression and impulsivity associated with ASPD. Treatment models employing methods from Cognitive Behavioural Therapy have been developed, and some reports suggest that this approach may be beneficial (Black, 2017). CognitiveBehaviour Therapy may be helpful for those with milder syndromes. Davidson et al (2009) investigated the effectiveness of CBT by carrying out a randomised controlled trial on men with ASPD who were aggressive. Their study showed that CBT did not improve outcomes more than usual treatment for men with ASPD who are aggressive and living in the community, thus indicating that CBT may not always be an effective approach to treating ASPD. However, there is generally a lack of information and study on the effectiveness of other potential treatments for ASPD.

Most people who have ASPD are undiagnosed because they believe that they do not need any treatment. Therefore, the individuals who have been diagnosed are usually those who have committed crimes and have entered the criminal justice system, where they are diagnosed and receive treatment. In the criminal justice system, patients are given either group-based Cognitive  Behavioural interventions, reasoning and rehabilitation programs, therapeutic community interventions, or pharmacological interventions. 

In a literature review conducted by the National Collaborating Centre for Mental Health, these treatment methods were evaluated and analysed for their effectiveness in treating ASPD. (National Collaborating Centre for Mental Health UK, 2010). Group-based Cognitive Behavioural interventions are mainly used to reduce patients’ impulsivity and interpersonal difficulties. On the other hand, the reasoning and rehabilitation programs are more effective in decreasing violent behaviours in ASPD patients, particularly crimes . Although both types of treatment address the behavioural components of ASPD, they target different aspects of the behaviour. The effectiveness of these treatment methods would greatly depend on the specific individual and what symptoms they are experiencing. Another type of treatment that is often used for ASPD patients is therapeutic community interventions (National Collaborating Centre for Mental Health UK, 2010). This is where patients are put into residential communities, where they learn social skills and norms, and increase their responsibility levels to spark change in their antisocial behaviour. Patients also undergo one-on-one keyworking with a therapist to develop practical skills, interests, and education. However studies have shown that there were no significant differences between those who were in a therapeutic community compared to those who received treatment in a regular prison service (National Collaborating Centre for Mental Health UK, 2010). Lastly, pharmacological interventions would be used if the patient had severe dysregulation of mood or anxiety. ASPD patients would be given selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants, venlafaxine or monoamine oxidase inhibitors to regulate mood and anxiety. A disadvantage of medication is that it doesn’t treat the underlying cause of the disorder (National Collaborating Centre for Mental Health UK, 2010). 

In summary, treatment for Cluster B disorders aims to raise awareness about how individuals’ interpretations of their interactions with others result in behaviours that negatively affect their relationships. As people with Cluster B disorders struggle with regulating intense emotions that arise suddenly, a key goal is to identify the intensifying of emotions before they escalate to the point that they cannot be controlled. As childhood trauma is often at the root of these disorders, disentangling old ways of viewing the world as hostile helps to allow individuals to see new situations as less threatening. Therapy usually cannot “cure” these disorders, but helps people to manage themselves better. ASPD, Borderline and Narcissistic disorders still remain difficult to treat.

Cluster C Disorders

Cluster C personality disorders are anxiety based disorders and therefore psychotherapy aims to reduce these symptoms. A study comparing the effectiveness of 5 psychotherapeutic treatment modalities for Cluster C patients found that patients in all treatment groups had improved on all outcomes after 12 months. Patients receiving short-term inpatient treatment demonstrated greater improvement rates than patients receiving any other treatment modalities. This evidence would suggest that  psychotherapeutic treatment, particularly in the short-term inpatient modality, is an effective treatment for people suffering from personality disorders in Cluster C (Bartak et al., 2009).

Obsessive Compulsive Personality Disorder does not have a definitive empirically supported treatment, despite OCPD patients often presenting themselves for treatment.  In a case report, a man with OCPD underwent a novel therapeutic intervention which consisted of two CBT modules: a module on CBT for clinical perfectionism/rigidity, preceded by a skills training module on emotional regulation and relationship flexibility (Pinto, 2015). The different modules of the 14-week treatment program were chosen to target  the aspects of OCPD that directly impact normal functioning. The patient was adherent and highly engaged in the treatment. He showed clinically significant improvement, which was maintained for 2 months post treatment. Although the results from this particular pilot are promising, there is a vital need for further research to allow for the appropriate treatments to be developed (Pinto, 2015).

Evidence suggests that Cognitive Behavioural Therapy is currently the best treatment of OCPD. However, various factors, such as self-esteem variability, early alliances, and distress level, appear to predict CBT outcomes, thus indicating that the effectiveness of CBT differs on an individual basis (Diedrich, 2015). Additionally, OCPD inpatients may benefit from an intensive multimodal psychiatric treatment (Smith et al., 2017). Strauss et al. (2006) conducted a CBT trial on 16 OCPD patients. Following CBT treatment, 53% of these patients showed a clinically significant decrease in depressive symptoms, and 83% showed clinically significant decreases in OCPD symptoms.  This suggests that CBT is effective in treating OCPD (Bhukhari et al., 2018). Diedrich’s (2005) finding that various individual factors predict CBT outcomes may explain why not all of the patients showed significant improvements following treatment.

SSRI medication has also been used to treat OCPD. Ansseau (1994) treated four outpatients with Obsessive Compulsive Personality Disorder with the SSRI fluvoxamine for a 3-month period. This study found that the ratings of DSM-IIIR individual criteria showed significant improvement following SSRI treatment, which suggests that serotonergic dysfunction does play a role in OCPD, and indicates that there is some evidence for the effectiveness of SSRIs as a treatment option (Ansseau, 1994).

Overall, milder experiences of Cluster B and C disorders are generally more treatable, although they are never “cured”.



This investigation looked into the causes and treatments for Cluster B and C personality disorders and the differences between the two Clusters. We researched this by exploring previous literature regarding the personality disorders in each Cluster and summarised the key findings to make a comparison between the two. 

Understanding the development of personality disorders and other mental health issues requires an examination of environmental and biological factors that may cause them. The strongest environmental factor shared by both Cluster B and C personality disorders was childhood abuse and poor parenting, resulting in trauma. The role of trauma is quite prevalent in causing Cluster B and C personality disorders. Both clusters have been shown to be triggered by some sort of trauma experienced at an earlier stage of life. ASPD is heavily associated with more severe forms of childhood trauma, especially sexual abuse. The earlier the onset of trauma, the more diverse types of traumatic experiences and the longer the duration, the more complex the trauma can be, which increases the risk of developing a personality disorder and distorted view of the world.

As the brain is a living organ that develops in response to the environment, abusive parenting has the potential to affect the normal growth of the emotional and decision-making parts of the brain. However, not all children who experience abuse end up with a personality disorder. Whether or not someone develops a personality disorder following childhood abuse and trauma is greatly affected by biological factors, such as the temperament they are born with (inhibited vs uninhibited) and their genes and heritability (likelihood that other family members have mental health issues or disorders). The more psychologically and biologically vulnerable and less resilient a child is, the greater the risk of developing a personality disorder. When brain development is affected, it is visible in behaviours (e.g. ,inability to manage intense fear, anger, hostility, aggression, anxiety etc.), as well as in brain scans.

It was found that both Cluster B and C personality disordered patients have abnormalities in the amygdala – the area of the brain regulating emotion. Furthermore, the orbitofrontal cortex (decision-making part of the brain) was found to be located at a lower area in Cluster B patients. In AVPD, there seems to be a positive correlation between the volume of grey matter and anxiety levels. Spontaneous brain activity was found in OCPD patients, while in an experiment with reward and loss tasks Cluster B patients showed a lack of activity in the prefrontal area of the brain (Lei et al., 2020). Another difference between the two Clusters is that the abnormalities of the amygdala in Cluster B patients mainly impacts the impulsiveness of patients whereas this impact is predominantly on anxiety for Cluster C patients.

Overall, prevalence rates of Cluster C PDs exceed those of Cluster B PDs (2.7% vs. 1.5%). However, Cluster B PDs represent a more severe disease category with respect to alcohol and drug use, and lifetime suicide attempts. Some argue that this justifies the specialised treatment programs for Cluster B PDs that target these specific symptoms, which are more studied and available than treatment programs for Cluster C PDs. Relative to Cluster C disorders, Cluster B personality disorders have a higher correlation with suicide attempts (Massaal-van der Ree et al., 2022). High rates of Childhood traumatization (CT) are found in both Cluster B and C PDs and are related to a less favourable course of progression and a negative treatment outcome (Massaal-van der Ree et al., 2022). 

As for treatment, both Cluster B and C personality disorders have been mainly treated using Cognitive Behavioural Therapy (Beck, 1990). However, more specialised treatments have been developed for many Cluster B disorders, and particularly for BPD, some of which have been suggested to be more effective than CBT. These are Dialectical Behavioural Therapy (DBT), Schema Therapy, and Mentalization Based Therapy (MBT). The main goal of therapy is to raise awareness of dysfunctional thinking patterns that cause greater emotional reactions, which are harder to control. Therefore, encouragement to change perspectives, and help in developing emotional self-control are key to effective therapy. Not all Cluster B and C disorders can be treated effectively, however. Research has shown that personality disorders such as ASPD and OCPD are quite hard to treat and don’t have a definitive empirically supported method of treatment. Because of the lack of effectiveness of the treatment of these disorders, it makes it extremely difficult for patients diagnosed with them to cope. Future research regarding this topic could explore other factors that may influence the development of personality disorders such as gender, ethnicity, and more. It is important for more research to be conducted on personality disorders, as it can make a huge impact on people’s lives. 



Adverse experiences such as childhood traumas and unstable family environments can increase a patient’s likelihood of developing Cluster B and Cluster C personality disorders. In Cluster B and Cluster C personality disorders, prevention of the development of the mental disorders is essential. Whilst no individual should be subject to any form of abuse, abuse cannot be entirely avoided for all individuals, as many factors such as culture and family situation can result in an individual being subject to adverse experiences. Therefore, early detection of abuse and a collective responsibility to take preventative action is essential in preventing the development of Cluster B and Cluster C personality disorders. 

One example of how this could be done is in medical care facilities, where red flags for physical child abuse should be identified. During physical examinations “an abused child may have soft-tissue injuries, rib fracture, or other long-bone fractures in various stages of healing” (Staheli, 2007). As individuals, we can also contribute to a collective prevention mechanism by detecting red flags for abuse and unstable family environments, and involving schools and child protection services if necessary. In detecting and preventing the aggravation of abuse and unstable family environments as well as in providing adequate support to individuals who have fallen victim to these, a lasting impact can be made on an individual’s life in reducing their likelihood of developing Cluster B and Cluster C personality disorders. Interventions to educate and support families are vital regardless of their socioeconomic status, as abuse is prevalent across SES, gender and culture.


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