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.

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.

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.

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.

Although there is no known cause for piblokto, Western scientists have attributed the disorder to the lack of sun, the extreme cold, and the desolate state of most villages in the region. A reason for this disorder present in this culture may be due to the isolation of their cultural group.

This culture-bound syndrome is possibly linked to vitamin A toxicity (hypervitaminosis A). The native Inughuit diet or Eskimo nutrition provides rich sources of vitamin A through the ingestion of livers, kidneys, and fat of arctic fish and mammals and is possibly the cause or a causative factor. This causative factor is through the disturbance that has been reported for males, females, adults, children, and dogs. The ingestion of organ meats, particularly the livers of some Arctic mammals, such as the polar bear and bearded seal, where the vitamin is stored in toxic quantities, can be fatal to most people.

Inughuit tradition states that it is caused by evil spirits possessing the living. Shamanism and animism are dominant themes in Inughuit traditional beliefs with the angakkuq (healer) acting as a mediator with the supernatural forces. Angakkuit use trance states to communicate with spirits and carry out faith healing. There is a view among the Inughuit that individuals entering trance states should be treated with respect given the possibility of a new "revelation" emerging as a result. Treatment in piblokto cases usually involves allowing the episode to run its course without interference. While piblokto can often be confused with other conditions, (including epilepsy) in which failure to intervene can lead to the victim coming to harm, most cases tend to be more typical.

Empirical studies have found that the prognosis for conversion disorder varies widely, with some cases resolving in weeks, and others enduring for years or decades. There is also evidence that there is no cure for Conversion Disorder, and that although patients may go into remission, they can relapse at any point. Furthermore, many patients who are 'cured' continue to have some degree of symptoms indefinitely.

Information on the frequency of conversion disorder in the West is limited, in part due to the complexities of the diagnostic process. In neurology clinics, the reported prevalence of unexplained symptoms among new patients is very high (between 30 and 60%). However, diagnosis of conversion typically requires an additional psychiatric evaluation, and since few patients will see a psychiatrist it is unclear what proportion of the unexplained symptoms are actually due to conversion. Large scale psychiatric registers in the US and Iceland found incidence rates of 22 and 11 newly diagnosed cases per 100,000 person-years, respectively. Some estimates claim that in the general population, between 0.011% and 0.5% of the population have conversion disorder.

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.

During a period of 13 years (1980–1993) for which admissions to the Kfar Shaul Mental Health Centre in Jerusalem were analysed, it was reported that 1,200 tourists with severe, Jerusalem-themed mental problems were referred to this clinic. Of these, 470 were admitted to hospital. On average, 100 such tourists have been seen annually, 40 of them requiring admission to hospital. About three and a half million tourists visit Jerusalem each year. Kalian and Witztum note that as a proportion of the total numbers of tourists visiting the city, this is not significantly different from any other city.

Piblokto, also known as pibloktoq and Arctic hysteria, is a condition most commonly appearing in Inughuit (Greenlandic Inuit) societies living within the Arctic Circle. Piblokto is a culture-specific hysterical reaction in Inuit, especially women, who may perform irrational or dangerous acts, followed by amnesia for the event. Piblokto may be linked to repression of the personality of Inuit women. The condition appears most commonly in winter. It is considered to be a form of a culture-bound syndrome, although more recent studies (see "Skepticism" section) question whether it exists at all. Piblokto is also part of the glossary of cultural bound syndromes found in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV).

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.

Recorded incidents of "amafufunyana" appear to have begun in the early 20th century and researchers such as Ngubane "et al" have suggested that its cultural formation may have had something to do with colonialism and migration of indigenous peoples away from their homes. There have also been widespread outbreaks of the condition, similar to events involving contagious spread of hysteria, recorded in the 1980s at a rural girl's boarding school.

The most common types of people that are identified as afflicted by the cultural group are those of the lowest economic and social level and more often during times of cultural hardship and change, such as during migrations. More women than men are also identified.

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.

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.

This syndrome is most commonly diagnosed when the two or more individuals concerned live in proximity and may be socially or physically isolated and have little interaction with other people. Various sub-classifications of "folie à deux" have been proposed to describe how the delusional belief comes to be held by more than one person :

- Folie imposée is where a dominant person (known as the 'primary', 'inducer' or 'principal') initially forms a delusional belief during a psychotic episode and imposes it on another person or persons (known as the 'secondary', 'acceptor' or 'associate') with the assumption that the secondary person might not have become deluded if left to his or her own devices. If the parties are admitted to hospital separately, then the delusions in the person with the induced beliefs usually resolve without the need of medication.

- Folie simultanée describes either the situation where two people considered to suffer independently from psychosis influence the content of each other's delusions so they become identical or strikingly similar, or one in which two people "morbidly predisposed" to delusional psychosis mutually trigger symptoms in each other.

Folie à deux and its more populous cousins are in many ways a psychiatric curiosity. The current Diagnostic and Statistical Manual of Mental Disorders states that a person cannot be diagnosed as being delusional if the belief in question is one "ordinarily accepted by other members of the person's culture or subculture" (see entry for delusion). It is not clear at what point a belief considered to be delusional escapes from the "folie à..." diagnostic category and becomes legitimate because of the number of people holding it. When a large number of people may come to believe obviously false and potentially distressing things based purely on hearsay, these beliefs are not considered to be clinical delusions by the psychiatric profession and are labelled instead as mass hysteria.

Amafufunyana is an unspecified "culture-bound" syndrome named by the traditional healers of the Xhosa people that relates to claims of demonic possession due to members of the Xhosa people exhibiting aberrant behavior and psychological concerns. After study, it was discovered that this term is directed toward people suffering from varying types of schizophrenia. A similar term, ukuthwasa, is used to refer to positive types of claimed possession, though this event also involves those suffering from schizophrenia. It has also found cultural usage among some groups of Zulu peoples.

The direct translation of the term "amafufunyana" is nerves and is a part of a much more complex cultural ideology connecting varying types of psychosis with religious, social, and recently psychiatric beliefs and activities. In a 1998 interview with Xhosa people suffering from schizophrenia by Lund et al., it was determined that through interaction with scientists and psychological services, the preferred treatment for the cultural condition had shifted from relation to traditional healers to active psychiatric assessment.

Psychosexual conflicts, personality factors, and cultural beliefs are considered as being of etiological

significance to koro. Sexual adjustment histories of non-Chinese victims are often significant, such as premorbid sex inadequacy, sexual promiscuity, guilt over masturbation, and impotence.

"Jerusalem syndrome as a discrete form, uncompounded by previous mental illness." This describes the best-known type, whereby a previously mentally balanced person becomes psychotic after arriving in Jerusalem. The psychosis is characterised by an intense religious character and typically resolves to full recovery after a few weeks or after being removed from the locality. It shares some features with the diagnostic category of a "brief psychotic episode", although a distinct pattern of behaviors has been noted:

1. Anxiety, agitation, nervousness and tension, plus other unspecified reactions.

2. Declaration of the desire to split away from the group or the family and to tour Jerusalem alone. Tour guides aware of the Jerusalem syndrome and of the significance of such declarations may at this point refer the tourist to an institution for psychiatric evaluation in an attempt to preempt the subsequent stages of the syndrome. If unattended, these stages are usually unavoidable.

3. A need to be clean and pure: obsession with taking baths and showers; compulsive fingernail and toenail cutting.

4. Preparation, often with the aid of hotel bed-linen, of a long, ankle-length, toga-like gown, which is always white.

5. The need to shout psalms or verses from the Bible, or to sing hymns or spirituals loudly. Manifestations of this type serve as a warning to hotel personnel and tourist guides, who should then attempt to have the tourist taken for professional treatment. Failing this, the two last stages will develop.

6. A procession or march to one of Jerusalem's holy places, ex:The Western Wall.

7. Delivery of a sermon in a holy place. The sermon is typically based on a plea to humankind to adopt a more wholesome, moral, simple way of life. Such sermons are typically ill-prepared and disjointed.

8. Paranoid belief that a Jerusalem syndrome agency is after the individual, causing their symptoms of psychosis through poisoning and medicating.

Bar-El et al. reported 42 such cases over a period of 13 years, but in no case were they able to actually confirm that the condition was temporary.

Hysteria, in the colloquial use of the term, means ungovernable emotional excess. Generally, modern medical professionals have abandoned using the term "hysteria" to denote a diagnostic category, replacing it with more precisely defined categories, such as somatization disorder. In 1980, the American Psychiatric Association officially changed the diagnosis of "hysterical neurosis, conversion type" (the most extreme and effective type) to "conversion disorder".

While the word "hysteria" originates from the Greek word for uterus, "hystera", the word itself is not an ancient one, and the term "hysterical suffocation" - meaning a feeling of heat and inability to breathe - was instead used in ancient Greek medicine. This suggests an entirely physical cause for the symptoms but, by linking them to the uterus, suggests that the disorder can only be found in women. Historically, hysteria was thought to manifest itself in women with a variety of symptoms, including: anxiety, shortness of breath, fainting, insomnia, irritability, nervousness, as well as sexually forward behaviour. These symptoms mimic symptoms of other more definable diseases and create a case for arguing against the validity of hysteria as an actual disease, and it is often implied that it is an umbrella term, used to describe an indefinable illness. Through to the 20th century, however, the label hysteria was applied to a mental, rather than uterine or physical, affliction. Hysteria is no longer thought of as a real ailment.

The history of hysteria has seen the approach of Ilza Veith, in which there is one disorder constant across time, and in which Freud is the hero with history becoming a steady progress towards his insights, replaced in the 1990s by scholarship based on closer knowledge of the original source texts. Through its lack of use as a medical diagnosis the term ‘hysteria’ now has connotations of mass panic, imagined or real. The term when applied to a singular person can mean that they are emotional or irrationally upset; when applied to a situation, it denotes it as funny.

Reports have stated that a similar phenomenon to "folie à deux" had been induced by the military incapacitating agent BZ in the late 1960s.

Neurosis is a class of functional mental disorders involving chronic distress but neither delusions nor hallucinations. The term is no longer used by the professional psychiatric community in the United States, having been eliminated from the "Diagnostic and Statistical Manual of Mental Disorders" in 1980 with the publication of DSM III. It is still used in the .

Neurosis should not be mistaken for psychosis, which refers to a loss of touch with reality. Neither should it be mistaken for neuroticism, a fundamental personality trait proposed in the big Five personality traits theory.

Pseudoneurotic schizophrenia is a postulated mental disorder categorized by the presence of two or more symptoms of mental illness such as anxiety, hysteria, and phobic or obsessive-compulsive neuroses. It is often acknowledged as a personality disorder. Patients generally display salient anxiety symptoms that disguise an underlying psychotic disorder.

In the 1940s, psychiatrists Paul Hoch and Philip Polatin created the term pseudoneurotic schizophrenia. This mental illness, however, is no longer acknowledged as a clinical entity. In 1972 it went on to be called borderline personality disorder, a term coined by Otto Friedmann Kernberg, which referred to an expansive range of issues.

Pseudoneurotic schizophrenia is in the Russian adapted version of the ICD-10 (code F21.3).

With the advent of industrialization came the mechanization of massage therapy, the steam powered 'Manipulator’ table massager created in the late 1860s and other devices similar in nature were becoming more available in the mid 19th century. Doctors could now increase their patient load by either investing in a portable vibratory device or having one installed in their office. This new technology also allowed husbands whose wives had been diagnosed with hysteria to partake in the treatments at home. This kind of treatment to induce what is now realized to be an orgasm in women was not considered a sexual act as, with the androcentric model for sexuality, it wasn't considered a true sexual act unless there was penetration and ejaculation. Other mechanized forms of treatment in the mid 19th century included Hydrotherapy with a pelvic douche massager, where cold water was blasted at a high pressure at a woman's abdomen. These devices were harder to sell to doctor’s offices because of the expense and the equipment needed to produce the right amount of water pressure, so spas took up the practice offering it not just as muscle therapy but also for treatment of hysteria.

When considering the biological mechanisms and evolutionary history of koro, it is important to look at it in the larger framework of mass hysteria. While the underlying mechanisms are still poorly understood, it has been suggested that the mirror neurons play a major role in mass hysteria outbreaks. Mirror neurons, which have been found in both human and non-human primates, are neurons that fire when one performs an action and when they observe another individual performing the same action. It is hypothesized that we evolved these mechanisms to learn from observation of others, as well as to facilitate imitation. However, within mirror neurons, there is some form of inhibitory process, which prevents us from blindly mimicking every action we observe others perform. New research into this area suggests that in mass hysteria outbreaks something goes amiss in this inhibitory process.

The hypothesis that those prone to extroversion or neuroticism, or those with low IQ scores, are more likely to be affected in an outbreak of hysterical epidemic has not been consistently supported by research. Bartholomew and Wesseley state that it “seems clear that there is no particular predisposition to mass sociogenic illness and it is a behavioural reaction that anyone can show in the right circumstances.”

Females are affected with mass psychogenic illness at greater rates than males. Adolescents and children are frequently affected in cases of MPI.