Environmental factors associated with the development of schizophrenia include the living environment, drug use, and prenatal stressors.

Maternal stress has been associated with an increased risk of schizophrenia, possibly in association with reelin. Maternal Stress has been observed to lead to hypermethylation and therefore under-expression of reelin, which in animal models leads to reduction in GABAergic neurons, a common finding in schizophrenia. Maternal nutritional deficiencies, such as those observed during a famine, as well as maternal obesity have also been identified as possible risk factors for schizophrenia. Both maternal stress and infection have been demonstrated to alter fetal neurodevelopment through pro-inflammatory proteins such as IL-8 and TNF.

Parenting style seems to have no major effect, although people with supportive parents do better than those with critical or hostile parents. Childhood trauma, death of a parent, and being bullied or abused increase the risk of psychosis. Living in an urban environment during childhood or as an adult has consistently been found to increase the risk of schizophrenia by a factor of two, even after taking into account drug use, ethnic group, and size of social group. Other factors that play an important role include social isolation and immigration related to social adversity, racial discrimination, family dysfunction, unemployment, and poor housing conditions.

It has been hypothesized that in some people, development of schizophrenia is related to intestinal tract dysfunction such as seen with non-celiac gluten sensitivity or abnormalities in the intestinal flora. A subgroup of persons with schizophrenia present an immune response to gluten different from that found in people with celiac, with elevated levels of certain serum biomarkers of gluten sensitivity such as anti-gliadin IgG or anti-gliadin IgA antibodies.

About half of those with schizophrenia use drugs or alcohol excessively.

Amphetamine, cocaine, and to a lesser extent alcohol, can result in a transient stimulant psychosis or alcohol-related psychosis that presents very similarly to schizophrenia. Although it is not generally believed to be a cause of the illness, people with schizophrenia use nicotine at much higher rates than the general population.

Alcohol abuse can occasionally cause the development of a chronic, substance-induced psychotic disorder via a kindling mechanism. Alcohol use is not associated with an earlier onset of psychosis.

Cannabis can be a contributory factor in schizophrenia, potentially causing the disease in those who are already at risk. The increased risk may require the presence of certain genes within an individual or may be related to preexisting psychopathology. Early exposure is strongly associated with an increased risk. The size of the increased risk is not clear, but appears to be in the range of two to three times greater for psychosis. Higher dosage and greater frequency of use are indicators of increased risk of chronic psychoses.

Other drugs may be used only as coping mechanisms by individuals who have schizophrenia, to deal with depression, anxiety, boredom, and loneliness.

Schizophrenia disorders in children are rare. Boys are twice as likely to be diagnosed with childhood schizophrenia. There is often an disproportionately large number of males with childhood schizophrenia, because the age of onset of the disorder is earlier in males than females by about 5 years. People have been and still are reluctant to diagnose schizophrenia early on, primarily due to the stigma attached to it.

While very early-onset schizophrenia is a rare event, with prevalence of about 1:10,000, early-onset schizophrenia is manifests more often with an estimated prevalence of 0.5 %.

There is no known single cause or causes of schizophrenia, however, it is a heritable disorder.

Several environmental factors, including perinatal complications and prenatal maternal infections could cause schizophrenia. These factors in a greater severity or frequency could result in an earlier onset of schizophrenia. Maybe a genetic predisposition is a important factor too, familial illness reported for childhood-onset schizophrenic patients.

According to the Mayo Clinic, it is best to start receiving treatment for paranoid schizophrenia as early as possible and to maintain the treatment throughout life. Continuing treatment will help keep the serious symptoms under control and allow the person to lead a more fulfilling life. This illness is typically unpreventable.

It has a strong hereditary component with a first degree parent or sibling. There is some possibility that there are environmental influences including "prenatal exposure to a viral infection, low oxygen levels during birth (from prolonged labor or premature birth), exposure to a virus during infancy, early parental loss or separation, and verbal, physical or sexual abuse in childhood". Eliminating any of these factors could help reduce an individual's future risk of developing paranoid schizophrenia.

Paranoid schizophrenia is an illness that typically requires lifelong treatment with neuroleptics to allow someone to have a relatively stable and normal lifestyle. In order to be successfully treated, a person with schizophrenia should seek help from family or primary care doctors, psychiatrists, psychotherapists, pharmacists, family members, case workers, psychiatric nurses, or social workers, provided he or she is not unable to do so, due to many people with schizophrenia having the inability to accept their condition. Non-compliance with neuroleptics may also occur if the patient considers the side effects (such as extrapyramidal symptoms) to be more debilitating than the condition itself. The main options that are offered for the treatment of paranoid schizophrenia are the following: neuroleptics, psychotherapy, hospitalization, electroconvulsive therapy, and vocational skills training.

There are many different types of disorders that have similar symptoms to paranoid schizophrenia. There are tests that psychiatrists perform to achieve a correct diagnosis. They include "psychiatric evaluation, in which the doctor or psychiatrist will ask a series of questions about the patient's symptoms, psychiatric history, and family history of mental health problems; medical history and exam, in which the doctor will ask about one's personal and family health history and will also perform a complete physical examination to check for medical issues that could be causing or contributing to the problem; laboratory tests in which the doctor will order simple blood and urine tests can rule out other medical causes of symptoms".

There are side effects associated with antipsychotic medication. Neuroleptics can cause high blood pressure and high cholesterol. Many people who take them exhibit weight gain and have a higher risk of developing diabetes.

Studies suggest that the prevalence of paraphrenia in the elderly population is around 2-4%.

While paraphrenia can occur in both men and women, it is more common in women, even after the difference has been adjusted for life expectancies. The ratio of women with paraphrenia to men with paraphrenia is anywhere from 3:1 to 45:2

It has possibly the earliest onset compared to all other schizophrenias, considered to begin in some within childhood. Symptoms of "schizophrenia" "simplex" include an absence of will, impoverished thinking and flattening of affect. There is a gradual deterioration of functioning with increased amotivation and reduced socialization. It is considered to be rarely diagnosed and is a schizophrenia without psychotic symptoms.

In a study of patients in a Massachusetts hospital, persons suffering with "simple schizophrenia" were found to make attempts at reality fulfillment with respect to the more primitive needs; tending toward the achievement of fulfillment of these needs rather than engaging in fantasy as is typically found as a reaction to environmental stimuli by the psychotic person.

A paranoid reaction may be caused from a decline in brain circulation as a result of high blood pressure or hardening of the arterial walls.

Drug-induced paranoia, associated with amphetamines, methamphetamine and similar stimulants has much in common with schizophrenic paranoia; the relationship has been under investigation since 2012. Drug-induced paranoia has a better prognosis than schizophrenic paranoia once the drug has been removed. For further information, see Stimulant psychosis and Substance-induced psychosis.

Based on data obtained by the Dutch NEMISIS project in 2005, there was an association between impaired hearing and the onset of symptoms of psychosis, which was based on a five-year follow up. Some older studies have actually declared that a state of paranoia can be produced in patients that were under a hypnotic state of deafness. This idea however generated much skepticism during its time.

Simple-type schizophrenia is a sub-type of schizophrenia as defined in the International Classification of Diseases . It is not included in the current "Diagnostic and Statistical Manual of Mental Disorders" (DSM-5). Simple-type schizophrenia is characterized by negative ("deficit") symptoms, such as avolition, apathy, anhedonia, reduced affect display, lack of initiative, lack of motivation, low activity; with absence of hallucinations or delusions of any kind.

Social circumstances appear to be highly influential on paranoid beliefs. Based on data collected by means of a mental health survey distributed to residents of Ciudad Juárez, Chihuahua (in Mexico) and El Paso, Texas (in the United States), paranoid beliefs seem to be associated with feelings of powerlessness and victimization, enhanced by social situations. Potential causes of these effects included a sense of believing in external control, and mistrust which can be strengthened by lower socioeconomic status. Those living in a lower socioeconomic status may feel less in control of their own lives. In addition, this study explains that females have the tendency to believe in external control at a higher rate than males, potentially making females more susceptible to mistrust and the effects of socioeconomic status on paranoia.

Emanuel Messinger reports that surveys have revealed that those exhibiting paranoia can evolve from parental relationships and dis-trustworthy environments. These environments could include being very disciplinary, stringent, and unstable. It was even noted that, "indulging and pampering (thereby impressing the child that he is something special and warrants special privileges)," can be contributing backgrounds. Experiences likely to enhance or manifest the symptoms of paranoia include increased rates of disappointment, stress, and a hopeless state of mind.

Discrimination has also been reported as a potential predictor of paranoid delusions. Such reports that paranoia seemed to appear more in older patients who had experienced higher levels of discrimination throughout their lives. In addition to this it has been noted that immigrants are quite susceptible to forms of psychosis. This could be due to the aforementioned effects of discriminatory events and humiliation.

The causes of melancholic-type major depressive disorder are believed to be mostly biological factors; some may have inherited the disorder from their parents. Sometimes stressful situations can trigger episodes of melancholic depression, though this is a contributing cause rather than a necessary or sufficient cause. People with psychotic symptoms are also thought to be more susceptible to this disorder. It is frequent in old age and often unnoticed by some physicians who perceive the symptoms to be a part of dementia. Major depressive disorder, melancholic or otherwise, is a separate condition that can be comorbid with dementia in the elderly.

Melancholic depression, or depression with melancholic features, is a DSM-IV subtype of clinical depression requiring at least one of the following symptoms:

- Anhedonia (the inability to find pleasure in positive things)

- Lack of mood reactivity (i.e. mood does not improve in response to positive events)

And at least three of the following:

- Depression that is subjectively different from grief or loss

- Severe weight loss or loss of appetite

- Psychomotor agitation or retardation

- Early morning awakening

- Guilt that is excessive

- Worse mood in the morning

Melancholic features apply to an episode of depression that occurs as part of either major depressive disorder or bipolar disorder I or II.

Melancholic depression is often considered to be a biologically based and particularly severe form of depression. Treatment involves antidepressants, electroconvulsive therapy, or other empirically supported treatments such as cognitive behavioral therapy and interpersonal therapy for depression. A 2008 analysis of a large study of patients with unipolar major depression found a rate of 23.5% for melancholic features. It was the first form of depression extensively studied, and many of the early symptom checklists for depression reflect this.

The incidence of melancholic depression has been found to increase when the temperature and/or sunlight are low.

According to the DSM-IV, the "melancholic features" specifier may be applied to the following only:

1. Major depressive episode, single episode

2. Major depressive episode, recurrent episode

3. Bipolar I disorder, most recent episode depressed

4. Bipolar II disorder, most recent episode depressed

The onset of alcohol dementia can occur as early as age thirty, although it is far more common that the dementia will reveal itself anywhere from age fifty to age seventy. The onset and the severity of this type of dementia is directly correlated to the amount of alcohol that a person consumes over his or her lifetime.

Epidemiological studies show an association between long-term alcohol intoxication and dementia. Alcohol can damage the brain directly as a neurotoxin, or it can damage it indirectly by causing malnutrition, primarily a loss of thiamine (vitamin B1). Alcohol abuse is common in older persons, and alcohol-related dementia is under-diagnosed. A discredited French study claimed that moderate alcohol consumption (up to four glasses of wine per week) protected against dementia, whereas higher rates of consumption have conclusively been shown to increase the chances of getting it.

Dementia praecox (a "premature dementia" or "precocious madness") is a disused psychiatric diagnosis that originally designated a chronic, deteriorating psychotic disorder characterized by rapid cognitive disintegration, usually beginning in the late teens or early adulthood. Over the years, the term "dementia praecox" was gradually replaced by "schizophrenia", which remains in current diagnostic use.

The term "dementia praecox" was first used in 1891 by Arnold Pick (1851–1924), a professor of psychiatry at Charles University in Prague. His brief clinical report described the case of a person with a psychotic disorder resembling hebephrenia. German psychiatrist Emil Kraepelin (1856–1926) popularised it in his first detailed textbook descriptions of a condition that eventually became a different disease concept and relabeled as schizophrenia. Kraepelin reduced the complex psychiatric taxonomies of the nineteenth century by dividing them into two classes: manic-depressive psychosis and dementia praecox. This division, commonly referred to as the Kraepelinian dichotomy, had a fundamental impact on twentieth-century psychiatry, though it has also been questioned.

The primary disturbance in dementia praecox was seen to be a disruption in cognitive or mental functioning in attention, memory, and goal-directed behaviour. Kraepelin contrasted this with manic-depressive psychosis, now termed bipolar disorder, and also with other forms of mood disorder, including major depressive disorder. He eventually concluded that it was not possible to distinguish his categories on the basis of cross-sectional symptoms.

Kraepelin viewed dementia praecox as a progressively deteriorating disease from which no one recovered. However, by 1913, and more explicitly by 1920, Kraepelin admitted that while there may be a residual cognitive defect in most cases, the prognosis was not as uniformly dire as he had stated in the 1890s. Still, he regarded it as a specific disease concept that implied incurable, inexplicable madness.

Neurocognitive disorders can have numerous causes: genetics, brain trauma, stroke, and heart issues. The main causes are neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease because they affect or deteriorate brain functions. Other diseases and conditions that cause NDCs include vascular dementia, frontotemporal degeneration, Lewy body disease, prion disease, normal pressure hydrocephalus, and dementia/neurocognitive issues due to HIV infection. They may also include dementia due to substance abuse or exposure to toxins.

Neurocongnitive disorder may also be caused by brain trauma, including concussions and Traumatic Brain Injuries, as well as post-traumatic stress and alcoholism. This is referred to as amnesia, and is characterized by damage to major memory encoding parts of the brain such as the hippocampus. Difficulty creating recent term memories is called anterograde amnesia and is caused by damage to the hippocampus part of the brain, which is a major part of the memory process. Retrograde amnesia is also caused by damage to the hippocampus, but the memories that were encoded or in the process of being encoded in long term memory are erased

Often, apathy is felt after witnessing horrific acts, such as the killing or maiming of people during a war, e.g. posttraumatic stress disorder. It is also known to be a distinct psychiatric syndrome that is associated with many conditions, some of which are: CADASIL syndrome, depression, Alzheimer's disease, Chagas disease, Creutzfeldt–Jakob disease, dementia (and dementias such as Alzheimer's disease, vascular dementia, and frontotemporal dementia), Korsakoff's syndrome, excessive vitamin D, hypothyroidism, hyperthyroidism, general fatigue, Huntington's disease, Pick's disease, progressive supranuclear palsy (PSP), brain damage, schizophrenia, schizoid personality disorder, bipolar disorder, autism, ADHD, Asperger's syndrome, and others. Some medications and the heavy use of drugs such as opiates or GABA-ergic drugs may bring apathy as a side effect.

Delirium can be caused by the worsening of previous medical conditions, substance abuse or withdrawal, mental illness, severe pain, immobilization, sleep deprivation and hypnosis.

Other common causes that may increase the risk of delirium include infections of urinary tract, skin and stomach, pneumonia, old age, and poor nutrition.

Pseudodementia is a phenotype approximated by a wide variety of underlying disorders (1). Data indicate that some of the disorders that can convert to a pseudodementia-like presentation include depression (mood), schizophrenia, mania, dissociative disorders, Ganser syndrome, conversion reaction, and psychoactive drugs (2). Although the frequency distribution of disorders presenting as pseudodementia remains unclear, what is clear is that depressive pseudodementia, synonymously referred to as depressive dementia(3) or major depression with depressive dementia (4), represents a major subclass of the overarching category of pseudodementia (4).

It has long been observed that in the differential diagnosis between dementia and pseudodementia, depressive pseudodementia appears to be the single most difficult disorder to distinguish from nosologically established "organic" categories of dementia(5), especially degenerative dementia of the Alzheimer type (6).

Depressive Pseudodementia is a syndrome seen in older people in which they exhibit symptoms consistent with dementia but the cause is actually depression.

Older people with predominant cognitive symptoms such as loss of memory, and vagueness, as well as prominent slowing of movement and reduced or slowed speech, were sometimes misdiagnosed as having dementia when further investigation showed they were suffering from a major depressive episode. This was an important distinction as the former was untreatable and progressive and the latter treatable with antidepressant therapy or electroconvulsive therapy or both. In contrast to major depression, dementia is a progressive neurodegenerative syndrome involving a pervasive impairment of higher cortical functions resulting from widespread brain pathology.

Chronic hallucinatory psychosis is a psychosis subtype, classified under "Other nonorganic psychosis" by the . Other abnormal mental symptoms in the early stages are, as a rule, absent. The patient is most usually quiet and orderly, with a good memory.

It has often been a matter of the greatest difficulty to decide under which heading of the recognized classifications individual members of this group should be placed. As the hallucinations give rise to slight depression, some might possibly be included under melancholia. In others, paranoia may develop. Others, again, might be swept into the widespread net of dementia praecox. This state of affairs cannot be regarded as satisfactory, for they are not truly cases of melancholia, paranoia, dementia praecox or any other described affection.

This disease, as its name suggests, is a hallucinatory case, for it is its main feature. These may be of all senses, but auditory hallucinations are the most prominent. At the beginning, the patient may realize that the hallucination is a morbid phenomenon and unaccountable. They may claim to hear a "voice" speaking, though there is no one in the flesh actually doing so. Such a state of affairs may last for years and possibly, though rarely, for life, and the subject would not be deemed insane in the ordinary sense of the word.

It's probable, however, that this condition forms the first stage of the illness, which eventually develops on definite lines. What usually happens is the patient seeks an explanation for the hallucinations. As none is forthcoming he/she tries to account for their presence and the result is a delusion, and, most frequently, a delusion of persecution. Also, it needs to be noted that the delusion is a comparatively late arrival and is the logical result of the hallucinations.

The highest rates of delirium (often 50% to 75% of people) is seen among those who are critically ill in the intensive care unit (ICU) As a result, this was referred to as "ICU psychosis" or "ICU syndrome", terms largely abandoned for the more widely accepted term ICU delirium. Since the advent of validated and easy-to-implement delirium instruments for ICU patients such as the Confusion Assessment Method for the ICU (CAM-ICU) and the Intensive Care Delirium Screening Checkllist (IC-DSC)., of the hundreds of thousands of ICU patients who develop delirium in ICUs every year, it has been recognized that most of them belong to the hypoactive variety, which is easily missed and invisible to the managing teams unless actively monitored using such instruments. The causes of delirium in such patients depend on the underlying illnesses, new problems like sepsis and low oxygen levels, and the sedative and pain medicines that are nearly universally given to all ICU patients. Outside the ICU, on hospital wards and in nursing homes, the problem of delirium is also a very important medical problem, especially for older patients.

The most recent area of the hospital in which delirium is just beginning to be monitored routinely in many centers is the Emergency Department, where the prevalence of delirium among older adults is about 10%. A systematic review of delirium in general medical inpatients showed that estimates of delirium prevalence on admission ranged from 10 to 31%. About 5% to 10% of older adults who are admitted to hospital develop a new episode of delirium while in hospital. Estimates of the prevalence of delirium in nursing homes are between 10% to 45%.

While apathy and anxiety may appear to be separate, and different, states of being, there are many ways that severe anxiety can cause apathy. First, the emotional fatigue that so often accompanies severe anxiety leads to one's emotions being worn out, thus leading to apathy. Second, the low serotonin levels associated with anxiety often lead to less passion and interest in the activities in one's life which can be seen as apathy. Third, negative thinking and distractions associated with anxiety can ultimately lead to a decrease in one's overall happiness which can then lead to an apathetic outlook about one's life. Finally, the difficulty enjoying activities that individuals with anxiety often face can lead to them doing these activities much less often and can give them a sense of apathy about their lives. Even behavioral apathy may be found in individuals with anxiety in the form of them not wanting to make efforts to treat their anxiety.

Delirium arises through the interaction of a number of predisposing and precipitating factors. A predisposing factor might be any biological, psychological or social factor that increases an individual’s susceptibility to delirium. An individual with multiple predisposing factors is said to have "high baseline vulnerability". A precipitating factor is any biological, psychological or social factor that can trigger delirium. The division of causes into "predisposing" and "precipitating" is useful in order to assess an individual’s risk of suffering from delirium, and in guiding the management of delirium – however there may be a significant degree of overlap between the two categories.

Delirium most commonly affects the old age and those of ill health. Health results from physical and socioeconomic assets, and opposing factors come from physical and socioeconomic deficits. Individuals with significant predisposing factors don't compensate for physical or social stressors ("precipitating factors"). In such an individual, a single or mild precipitating factor could be sufficient to trigger an episode of delirium. Conversely, delirium may only result in a healthy individual if they suffer serious or multiple precipitating factors. It is important to note that the factors affecting those of an individual can change over time, thus an individual’s risk of delirium is in a state of flux.

Disorders that cause injury or damage to the brain and contribute to OBS include, but are not limited to:

- Alcoholism

- Alzheimer's Disease

- Attention deficit/hyperactivity disorder

- Autism

- Concussion

- Encephalitis

- Epilepsy

- Fetal alcohol syndrome

- Hypoxia

- Parkinson's disease

- Intoxication/overdose caused by drug abuse including alcoholism

- Sedative hypnotic dependence and drug abuse

- Intracranial hemorrhage/trauma

- Korsakoff Syndrome

- Mastocytosis

- Meningitis

- Psychoorganic syndrome

- Stroke/transient ischemic attack (TIA)

- Withdrawal from drugs, especially sedative hypnotics, e.g. alcohol or benzodiazepines

Other conditions that may be related to organic brain syndrome include: clinical depression, neuroses, and psychoses, which may occur simultaneously with the OBS.