Socioeconomic status has also been looked at as a potential cause for personality disorders. There is a strong association with low parental/neighborhood socioeconomic status and personality disorder symptoms. In a recent study comparing parental socioeconomic status and a child's personality, it was seen that children who were from higher socioeconomic backgrounds were more altuistic, less risk seeking, and had overall higher IQs. These traits correlate with a low risk of developing personality disorders later on in life. In a study looking at female children who were detained for disciplinary actions found that psychological problems were most negatively associated with socioeconomic problems. Furthermore, social disorganization was found to be inversely correlated with personality disorder symptoms.

Risk factors for mental illness include genetic inheritance, such as parents having depression, or a propensity for high neuroticism or "emotional instability".

In depression, parenting risk factors include parental unequal treatment, and there is association with high cannabis use.

In schizophrenia and psychosis, risk factors include migration and discrimination, childhood trauma, bereavement or separation in families, and abuse of drugs, including cannabis, and urbanicity.

In anxiety, risk factors may include family history (e.g. of anxiety), temperament and attitudes (e.g. pessimism), and parenting factors including parental rejection, lack of parental warmth, high hostility, harsh discipline, high maternal negative affect, anxious childrearing, modelling of dysfunctional and drug-abusing behaviour, and child abuse (emotional, physical and sexual).

Environmental events surrounding pregnancy and birth have also been implicated. Traumatic brain injury may increase the risk of developing certain mental disorders. There have been some tentative inconsistent links found to certain viral infections, to substance misuse, and to general physical health.

Social influences have been found to be important, including abuse, neglect, bullying, social stress, traumatic events and other negative or overwhelming life experiences. For bipolar disorder, stress (such as childhood adversity) is not a specific cause, but does place genetically and biologically vulnerable individuals at risk for a more severe course of illness. The specific risks and pathways to particular disorders are less clear, however. Aspects of the wider community have also been implicated, including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures.

Child abuse and neglect consistently show up as risk factors to the development of personality disorders in adulthood. A study looked at retrospective reports of abuse of participants that had demonstrated psychopathology throughout their life and were later found to have past experience with abuse. In a study of 793 mothers and children, researchers asked mothers if they had screamed at their children, and told them that they did not love them or threatened to send them away. Children who had experienced such verbal abuse were three times as likely as other children (who did not experience such verbal abuse) to have borderline, narcissistic, obsessive-compulsive or paranoid personality disorders in adulthood. The sexually abused group demonstrated the most consistently elevated patterns of psychopathology. Officially verified physical abuse showed an extremely strong correlation with the development of antisocial and impulsive behavior. On the other hand, cases of abuse of the neglectful type that created childhood pathology were found to be subject to partial remission in adulthood.

Individual differences in women's estrogen cycles may be related to the expression of BPD symptoms in female patients. A 2003 study found that women's BPD symptoms were predicted by changes in estrogen levels throughout their menstrual cycles, an effect that remained significant when the results were controlled for a general increase in negative affect.

Correlations of mental disorders with drug use include cannabis, alcohol and caffeine, use of which appears to promote anxiety. For psychosis and schizophrenia, usage of a number of drugs has been associated with development of the disorder, including cannabis, cocaine, and amphetamines. There has been debate regarding the relationship between usage of cannabis and bipolar disorder.

There is a strong correlation between child abuse, especially child sexual abuse, and development of BPD. Many individuals with BPD report a history of abuse and neglect as young children, but causation is still debated. Patients with BPD have been found to be significantly more likely to report having been verbally, emotionally, physically, or sexually abused by caregivers of either gender. They also report a high incidence of incest and loss of caregivers in early childhood. Individuals with BPD were also likely to report having caregivers of both sexes deny the validity of their thoughts and feelings. Caregivers were also reported to have failed to provide needed protection and to have neglected their child's physical care. Parents of both sexes were typically reported to have withdrawn from the child emotionally and to have treated the child inconsistently. Additionally, women with BPD who reported a previous history of neglect by a female caregiver and abuse by a male caregiver were significantly more likely to experience sexual abuse by a non-caregiver.

It has been suggested that children who experience chronic early maltreatment and attachment difficulties may go on to develop borderline personality disorder. Writing in the psychoanalytic tradition, Otto Kernberg argues that a child's failure to achieve the developmental task of and failure to overcome splitting might increase the risk of developing a borderline personality. A child's inability to tolerate delayed gratification at age four does not predict later development of BPD.

Reported prevalence of STPD in community studies ranges from 0.6% in a Norwegian sample, to 4.6% in an American sample. A large American study found a lifetime prevalence of 3.9%, with somewhat higher rates among men (4.2%) than women (3.7%). It may be uncommon in clinical populations, with reported rates of 0% to 1.9%.

Together with other Cluster A personality disorders, it is also very common among homeless people.

A University of Colorado Colorado Springs study comparing personality disorders and Myers-Briggs Type Indicator types found that the disorder had a significant correlation with the Introverted (I), Intuitive (N), Thinking (T), and Perceiving (P) preferences.

Genetic

Schizotypal personality disorder is widely understood to be a "schizophrenia spectrum" disorder. Rates of schizotypal personality disorder are much higher in relatives of individuals with schizophrenia than in the relatives of people with other mental illnesses or in people without mentally ill relatives. Technically speaking, schizotypal personality disorder may also be considered an "extended phenotype" that helps geneticists track the familial or genetic transmission of the genes that are implicated in schizophrenia. But there is also a genetic connection of STPD to mood disorders and depression in particular.

Social and environmental

There is now evidence to suggest that parenting styles, early separation, trauma/maltreatment history (especially early childhood neglect) can lead to the development of schizotypal traits. Neglect or abuse, trauma, or family dysfunction during childhood may increase the risk of developing schizotypal personality disorder. Over time, children learn to interpret social cues and respond appropriately but for unknown reasons this process does not work well for people with this disorder.

Schizotypal personality disorders are characterized by a common attentional impairment in various degrees that could serve as a marker of biological susceptibility to STPD. The reason is that an individual who has difficulties taking in information may find it difficult in complicated social situations where interpersonal cues and attentive communications are essential for quality interaction. This might eventually cause the individual to withdraw from most social interactions, thus leading to asociality.

The lifetime prevalence of dissociative disorders varies from 10% in the general population to 46% in psychiatric inpatients. Diagnosis can be made with the help of structured interviews such as the Dissociative Disorders Interview Schedule (DDIS) and the Structured Clinical Interview for DSM-IV Dissociative Disorders (SCID-D), or with the Dissociative Experiences Scale (DES) which is a self-assessment questionnaire. Some diagnostic tests have also been adapted and/or developed for use with children and adolescents such as the Children's Version of the Response Evaluation Measure (REM-Y-71), Child Interview for Subjective Dissociative Experiences, Child Dissociative Checklist (CDC), Child Behavior Checklist (CBCL) Dissociation Subscale, and the Trauma Symptom Checklist for Children Dissociation Subscale.

There are problems with classification, diagnosis and therapeutic strategies of dissociative and conversion disorders which can be understood by the historic context of hysteria. Even current systems used to diagnose DD such as the DSM-IV and ICD-10 differ in the way the classification is determined. In most cases mental health professionals are still hesitant to diagnose patients with Dissociative Disorder, because before they are considered to be diagnosed with Dissociative Disorder these patients have more than likely been diagnosed with major depression, anxiety disorder, and most often post-traumatic disorder.

An important concern in the diagnosis of dissociative disorders is the possibility that the patient may be feigning symptoms in order to escape negative consequences. Young criminal offenders report much higher levels of dissociative disorders, such as amnesia. In one study it was found that 1% of young offenders reported complete amnesia for a violent crime, while 19% claimed partial amnesia. There have also been incidences in which people with dissociative identity disorder provide conflicting testimonies in court, depending on the personality that is present.

Another theory suggests a possible relationship between histrionic personality disorder and antisocial personality disorder. Research has found 2/3 of patients diagnosed with histrionic personality disorder also meet criteria similar to those of the antisocial personality disorder, which suggests both disorders based towards sex-type expressions may have the same underlying cause. Women are hypersexualized in the media consistently, ingraining thoughts that the only way women are to get attention is by exploiting themselves, and when seductiveness isn't enough, theatricals are the next step in achieving attention. Men can just as well be flirtatious towards multiple women yet feel no empathy or sense of compassion towards them. They may also become the center of attention by exhibiting the "Don Juan" macho figure as a role-play.

Some family history studies have found that histrionic personality disorder, as well as borderline and antisocial personality disorders, tend to run in families, but it is unclear if this is due to genetic or environmental factors. Both examples suggest that predisposition could be a factor as to why certain people are diagnosed with histrionic personality disorder, however little is known about whether or not the disorder is influenced by any biological compound or is genetically inheritable. Little research has been conducted to determine the biological sources, if any, of this disorder.

The development of conduct disorder is not immutable or predetermined. A number of interactive risk and protective factors exist that can influence and change outcomes, and in most cases conduct disorder develops due to an interaction and gradual accumulation of risk factors. In addition to the risk factors identified under cause, several other variables place youth at increased risk for developing the disorder, including child physical abuse and prenatal alcohol abuse and maternal smoking during pregnancy. Protective factors have also been identified, and most notably include high IQ, being female, positive social orientations, good coping skills, and supportive family and community relationships.

However, a mere correlation between a particular risk factor and a later developmental outcome (such as conduct disorder) cannot be taken as definitive evidence for a causal link. Co-variation between two variables can arise, for instance, if they represent age-specific expressions of similar underlying genetic factors. For example, the tendency to smoke during pregnancy (SDP) is subject to substantial genetic influence (D'Onofrio et al., 2007), as is conduct disorder. Thus, the genes that dispose the mother to SDP may also dispose the child to CD following mitotic transmission. Indeed, Rice et al. (2009) found that in mother-fetus pairs that were not genetically related (by virtue of in-vitro fertilisation), no link between SDP and later conduct problems arose. Thus, the distinction between causality and correlation is an important consideration.

DID is rarely diagnosed in children, despite the average age of appearance of the first alter being three years. This fact is cited as a reason to doubt the validity of DID, and proponents of both etiologies believe that the discovery of DID in a child that had never undergone treatment would critically undermine the SCM. Conversely, if children are found to only develop DID after undergoing treatment it would challenge the traumagenic model. , approximately 250 cases of DID in children have been identified, though the data does not offer unequivocal support for either theory. While children have been diagnosed with DID before therapy, several were presented to clinicians by parents who were themselves diagnosed with DID; others were influenced by the appearance of DID in popular culture or due to a diagnosis of psychosis due to hearing voices—a symptom also found in DID. No studies have looked for children with DID in the general population, and the single study that attempted to look for children with DID not already in therapy did so by examining siblings of those already in therapy for DID. An analysis of diagnosis of children reported in scientific publications, 44 case studies of single patients were found to be evenly distributed (i.e., each case study was reported by a different author) but in articles regarding groups of patients, four researchers were responsible for the majority of the reports.

The initial theoretical description of DID was that dissociative symptoms were a means of coping with extreme stress (particularly childhood sexual and physical abuse), but this belief has been challenged by the data of multiple research studies. Proponents of the traumagenic hypothesis claim the high correlation of child sexual and physical abuse reported by adults with DID corroborates the link between trauma and DID. However, the DID-maltreatment link has been questioned for several reasons. The studies reporting the links often rely on self-report rather than independent corroborations, and these results may be worsened by selection and referral bias. Most studies of trauma and dissociation are cross-sectional rather than longitudinal, which means researchers can not attribute causation, and studies avoiding recall bias have failed to corroborate such a causal link. In addition, studies rarely control for the many disorders comorbid with DID, or family maladjustment (which is itself highly correlated with DID). The popular association of DID with childhood abuse is relatively recent, occurring only after the publication of "Sybil" in 1973. Most previous examples of "multiples" such as Chris Costner Sizemore, whose life was depicted in the book and film "The Three Faces of Eve", disclosed no history of child abuse.

Data from the 2001–02 National Epidemiologic Survey on Alcohol and Related Conditions indicates a prevalence rate of 2.36% in the American general population. It appears to occur with equal frequency in males and females. In one study, it was seen in 14.7% of psychiatric outpatients.

Little is known about prognosis of untreated DID. It rarely, if ever, goes away without treatment, but symptoms may resolve from time to time or wax and wane spontaneously. Patients with mainly dissociative and posttraumatic symptoms face a better prognosis than those with comorbid disorders or those still in contact with abusers, and the latter groups often face lengthier and more difficult treatment. Suicidal ideation, failed suicide attempts, and self-harm also occur. Duration of treatment can vary depending on patient goals, which can extend from elimination of all alters to merely reducing inter-alter amnesia, but generally takes years.

While the cause of conduct disorder is complicated by an intricate interplay of biological and environmental factors, identifying underlying mechanisms is crucial for obtaining accurate assessment and implementing effective treatment. These mechanisms serve as the fundamental building blocks on which evidence-based treatments are developed. Despite the complexities, several domains have been implicated in the development of conduct disorder including cognitive variables, neurological factors, intraindividual factors, familial and peer influences, and wider contextual factors. These factors may also vary based on the age of onset, with different variables related to early (e.g., neurodevelopmental basis) and adolescent (e.g., social/peer relationships) onset.

Dependent personality disorder occurs in about 0.6% of the general population. The disorder is diagnosed more often in females than males; however, research suggests that this is largely due to behavioural differences in interviews and self-reporting rather than a difference in prevalence between the sexes. A 2004 twin study suggests a heritability of 0.81 for developing dependent personality disorder. Because of this, there is significant evidence that this disorder runs in families. Children and adolescents with a history of anxiety disorders and physical illnesses are more susceptible to acquiring this disorder.

Externalizing disorders are frequently comorbid or co-occurring with other disorders. Individuals who have the co-occurrence of more than one externalizing disorder have homotypic comorbidity, whereas individuals who have co-occurring externalizing and Internalizing disorders have heterotypic comorbidity. It is not uncommon for children with early externalizing problems to develop both internalizing and further externalizing problems across the lifespan.

According to Professor Emily Simonoff of the Institute of Psychiatry, Psychology and Neuroscience, "childhood hyperactivity and conduct disorder showed equally strong prediction of antisocial personality disorder (ASPD) and criminality in early and mid-adult life. Lower IQ and reading problems were most prominent in their relationships with childhood and adolescent antisocial behaviour."

There is evidence that narcissistic personality disorder is heritable, and individuals are much more likely to develop NPD if they have a family history of the disorder. Studies on the occurrence of personality disorders in twins determined that there is a moderate to high heritability for narcissistic personality disorder.

However the specific genes and gene interactions that contribute to its cause, and how they may influence the developmental and physiological processes underlying this condition, have yet to be determined.

Because of reduced levels of trust, there can be challenges in treating PPD. However, psychotherapy, antidepressants, antipsychotics and anti-anxiety medications can play a role when an individual is receptive to intervention.

The causes of narcissistic personality disorder are unknown. Experts tend to apply a biopsychosocial model of causation, meaning that a combination of environmental, social, genetic and neurobiological factors are likely to play a role in formulating a narcissistic personality.

Dissociative disorders (DD) are widely believed to have roots in traumatic childhood experience (abuse or loss), but symptomology often goes unrecognized or is misdiagnosed in children and adolescents. There are several reasons why recognizing symptoms of dissociation in children is challenging: it may be difficult for children to describe their internal experiences; caregivers may miss signals or attempt to conceal their own abusive or neglectful behaviors; symptoms can be subtle or fleeting; disturbances of memory, mood, or concentration associated with dissociation may be misinterpreted as symptoms of other disorders.

In addition to developing diagnostic tests for children and adolescents (see above), a number of approaches have been developed to improve recognition and understanding of dissociation in children. Recent research has focused on clarifying the neurological basis of symptoms associated with dissociation by studying neurochemical, functional and structural brain abnormalities that can result from childhood trauma. Others in the field have argued that recognizing disorganized attachment (DA) in children can help alert clinicians to the possibility of dissociative disorders.

Clinicians and researchers also stress the importance of using a developmental model to understand both symptoms and the future course of DDs. In other words, symptoms of dissociation may manifest differently at different stages of child and adolescent development and individuals may be more or less susceptible to developing dissociative symptoms at different ages. Further research into the manifestation of dissociative symptoms and vulnerability throughout development is needed. Related to this developmental approach, more research is required to establish whether a young patient’s recovery will remain stable over time.

A genetic contribution to paranoid traits and a possible genetic link between this personality disorder and schizophrenia exist. A large long-term Norwegian twin study found paranoid personality disorder to be modestly heritable and to share a portion of its genetic and environmental risk factors with the other cluster A personality disorders, schizoid and schizotypal.

Psychosocial theories implicate projection of negative internal feelings and parental modeling. Cognitive theorists believe the disorder to be a result of an underlying belief that other people are unfriendly in combination with a lack in self-awareness.

Being a personality disorder, which are usually chronic and long-lasting mental conditions, avoidant personality disorder is not expected to improve with time without treatment. It is a poorly studied personality disorder and in light of prevalence rates, societal costs, and the current state of research, AvPD qualifies as a neglected disorder.

Approximately 1–3% of the general population may be diagnosed with HPD. Major character traits may be inherited, while other traits may be due to a combination of genetics and environment, including childhood experiences. This personality is seen more often in women than in men. It has typically been found that at least two thirds of persons with HPD are female, however there have been a few exceptions. Whether or not the rate will be significantly higher than the rate of women within a particular clinical setting depends upon many factors that are mostly independent of the differential sex prevalence for HPD. Those with HPD are more likely to look for multiple people for attention which leads to marital problems due to jealousy and lack of trust from the other party. This makes them more likely to become divorced or separated once married.