include maternal exposure to stress or trauma, conditions of famine, obstetric birth complications, infections, and gestational exposure to alcohol or cocaine. these factors have been hypothesized to affect areas of neurodevelopment, general development, and restrict neuroplasticity. infection, disease and toxins there have been some findings of links between infection by the parasite toxoplasma gondii and schizophrenia. aids has been linked to some mental disorders. research shows that infections and exposure to toxins such as hiv and streptococcus cause dementia. this hiv infection that makes its way to the brain is called encephalopathy which spreads itself through the brain leading to dementia. the infections or toxins that trigger a change in the brain chemistry can develop into a mental disorder. depression and emotional liability may be also be caused by babesiosis. there is some evidence that there may be a relationship between bodv-1 infection and psychiatric disease. the research on lyme disease caused by a deer tick and toxins is expanding the link between bacterial infections and mental illness. injury and brain defects any damage to the brain can cause a mental disorder. the brain is the control system for the nervous system and the rest of the body. without it, the body cannot function properly. increased mood swings, insane behavior, and substance abuse disorders are traumatic brain injury (tbi) examples. findings on the relationship between tbi severity and prevalence of subsequent psychiatric disorders have been inconsistent, and occurrence relates to prior mental health problems. direct neurophysiological effects in a complex interaction with personality, attitude, and social influences. head trauma classifies as either open or closed head injury. in open head injury, the skull is punctured and the brain tissue is demolished. closed head injury is more common, the skull is not punctured because there is an impact of the brain against the skull that creates permanent structural damage (subdural hematoma). with both types, symptoms may disappear or persist over time. typically the longer the length of time spent unconscious and the length of post-traumatic amnesia the worse the prognosis for the individual. the cognitive residual symptoms of head trauma are associated with the type of injury (either an open head injury or closed head injury) and the amount of tissue destroyed. closed injury head trauma symptoms include; deficits in abstract reasoning ability, judgment, memory, and marked personality changes. open injury head trauma symptoms tend to be the experience of classic neuropsychological syndromes like aphasia, visual-spatial disorders, and types of memory or perceptual disorders. brain tumors are classified as either malignant and benign, and as intrinsic (directly infiltrate the parenchyma of the brain) or extrinsic (grows on the external surface of the brain and produces symptoms as a result of pressure on the brain tissue). progressive cognitive changes associated with brain tumors may include confusion, poor comprehension, and even dementia. symptoms tend to depend on the location of the tumor in the brain. for example, tumors on the frontal lobe tend to be associated with the sign of impairment of judgment, apathy, and loss of the ability to regulate/modulate behavior. findings have indicated abnormal functioning of brainstem structures in individuals with mental disorders such as schizophrenia, and other disorders that have to do with impairments in maintaining sustained attention. some abnormalities in the average size or shape of some regions of the brain have been found in some disorders, reflecting genes and experiences. studies of schizophrenia have tended to find enlarged ventricles and sometimes reduced volume of the cerebrum and hippocampus, while studies of (psychotic) bipolar disorder have sometimes found increased amygdala volume. findings differ over whether volumetric abnormalities are risk factors or are only found alongside the course of mental health problems, possibly reflecting neurocognitive or emotional stress processes and medication use or substance use. some studies have also found reduced hippocampal volumes in major depression, possibly worsening with time depression. generic neurotransmitter system neurotransmitter systems abnormal levels of dopamine activity correspond with several disorders (reduced in adhd and ocd, and increased in schizophrenia). the dysfunction in serotonin and other monoamine neurotransmitters (norepinephrine and dopamine) correspond with certain mental disorders and their associated neural networks. some include major depression, obsessive-compulsive disorder, phobias, post-traumatic stress disorder, and generalized anxiety disorder. studies of depleted levels of monoamine neurotransmitters show an association with depression and other psychiatric disorders, but "... it should be questioned whether 5-ht represents just one of the final and not the main, factors in the neurological chain of events underlying psychopathological symptoms...." simplistic "chemical imbalance" explanations for mental disorders have never received empirical support; and most prominent psychiatrists, neuroscientists, and psychologists have not espoused such ill-defined, facile etiological theories. instead, neurotransmitter systems have been understood in the context of the diathesis-stress or biopsychosocial models. the following 1967 quote from renowned psychiatric and neuroscience researchers exemplifies this more sophisticated understanding (in contrast to the woolly "chemical imbalance" notion). whereas specific genetic factors may be of importance in the etiology of some, and possibly all, depressions, it is equally conceivable that early experiences of the infant or child may cause enduring biochemical changes, that may predispose some individuals to depressions in adulthood. it is not likely that changes in the metabolism of the biogenic amines alone will account for the complex phenomena of normal or pathological affect. substance abuse substance abuse, especially long-term abuse, can cause or exacerbate many mental disorders. alcoholism is linked to depression while abuse of amphetamines and lsd can leave a person feeling paranoid and anxious. correlations of mental disorders with drug use include cannabis, alcohol, and caffeine. at more than 300 mg, caffeine may cause anxiety or worsen anxiety disorders. illicit drugs can stimulate particular parts of the brain that can affect development in adolescence. cannabis has also been found to worsen depression and lessen an individual's motivation. alcohol has the potential to damage "white matter" in the brain that affects thinking and memory. alcohol is a problem in many countries due to many people participating in excessive drinking or binge drinking. environmental factors the term "environment" is very loosely defined in the context of mental illnesses. unlike biological and psychological causes, environmental causes denote a wide range of stressors that individuals experience in everyday life. they are more psychologically than biologically based. events that evoke feelings of loss are the most likely to cause a mental disorder to develop in an individual. environmental factors include but are not limited to dysfunctional home life, poor interpesonal relationships, substance abuse, not meeting social expectations, low self-esteem, and poverty. the british charity organisation mind lists childhood abuse, trauma, violence, neglect, social isolation, discrimination, grief, stress, homelessness, social disadvantage, debt, unemployment, caring for a family member or friend, and significant trauma as an adult (such as war, an accident, or being the victim of a violent crime) as possible triggers of an episode of mental illness. repeating generational patterns are also risk factor for mental illness. life events and emotional stress mistreatment in childhood or adulthood (including sexual-, physical-, and emotional abuse, domestic violence, and bullying) has been linked to the onset of mental disorders through an interaction of societal, familial, psychological, and biological factors. more generally, negative or stressful life events have been implicated in the development of a range of disorders, including mood and anxiety disorders. the main risks appear to be from the accumulation of such experiences over time, although a single major trauma can sometimes lead to disorders, especially post-traumatic stress disorder. resilience to such experiences varies; a person may be resistant to some stressors but not to others. the psychological resilience of an individual can be affected by genetics, temperamental characteristics, cognitive flexibility, coping strategies, and previous experiences. for example, in the case of bipolar disorder, stress is not a specific cause but does place genetically and biologically vulnerable people at risk for more severe forms of the illness. adverse childhood experiences main article: adverse childhood experiences further information: stress in early childhood and childhood schizophrenia the adverse childhood experiences study has shown a strong dose–response relationship between adverse childhood experiences or aces (such as physical and/or emotional neglect, abuse, poverty, malnutrition, and traumatic experiences) and numerous health, social, and behavioral problems including suicide attempts and the frequency of depressive episodes. several such experiences can cause toxic stress. aces may affect the structural and functional development of the brain and lead to abnormalities, and chronic trauma can disrupt immune responses and cause lasting dysregulated inflammatory response. a child's neurological development can be disrupted when chronically exposed to stressful events, and his/her cognitive functioning and/or ability to cope with negative emotions can diminish. over time, the child may adopt various harmful coping strategies that contribute to later mental and physical problems. findings have been mixed, but some studies suggest that cognitive deficit is more related to neglect than other forms of adversity. poor parenting is a risk factor for depression and anxiety. separation, grief in families, and other forms childhood trauma are risk factors for schizophrenia. children are more susceptible to psychological harm from traumatic events than adults, but their reaction does vary by individual child, age, the type of event, and the length of exposure. studies have shown that human-induced trauma affects children more than natural disasters. neglect is a form of mistreatment in which the responsible caretakers fail to provide the necessary age-appropriate care, supervision, and protection. it is different from abuse in that it is, in this context, not intentional in causing harms. the long-term effects of neglect can be reduced physical, emotional, and mental health throughout the victim's life. familial and close relationships parental divorce, death, absence, or the lack of continuity appears to increase the risk of mental disorders in a child. early social privation, and the lack of "ongoing, harmonious, secure, committed" relationships have been implicated in the development of mental illnesses. continuous conflict with friends, one's support system, and family can all increase the risk of developing a mental illness or can worsen one's mental health. divorce is a factor that affects adults as well as children. divorcees may have emotional adjustment problems due to a loss of intimacy and social connections; however, new statistics show that the negative effects of divorce have been overstated. social expectations and self-esteem having both too low or too high self-esteem can be detrimental to an individual's mental health. low self-esteem in particular can result in aggression, self-deprecating behavior, anxiety, and other mental disorders. being perceived as someone who does not "fit in" can result in bullying and other types of emotional abuse, which can lead to the victim experiencing depression, anger, and loneliness. poverty poor czech poor children in 1917. studies show that there is a direct correlation between poverty and mental illness: the lower the socioeconomic status of an individual, the higher the risk of mental illness. impoverished people are two to three times more likely to develop mental illness than those of a higher economic class. this increased risk remains consistent for all poor individuals regardless of any in-group demographic differences, as all disadvantaged families experience economic stressors such as unemployment or lack of housing. a lower or more insecure educational, occupational, economic, or social position is generally linked to more mental disorders. children from these bacgkrounds may have low levels of self-efficiency and self-worth. studies have also shown a strong relationship between poverty and substance abuse, another risk factor in the onset of mental disorders. problems in one's community or culture including poverty, unemployment or underemployment, a lack of social cohesion, and migration have been associated with the development of mental disorders. there have been mixed findings on the nature of the links and on the extent to which pre-existing personal characteristics influence them. personal resources, community factors, and interactions between individual and regional-level income levels have been implicated. socioeconomic deprivation in neighborhoods can cause worse mental health, even after accounting for genetic factors. the effects of different socioeconomic factors varies by country. minority ethnic groups, including first or second-generation immigrants, are at a greater risk of developing mental disorders. this has been attributed to the insecurities in their lives and their disadvantages, including racism. there have been alternate models, such as the drift hypothesis to account for the complex relationship between an individual's social status and mental health. psychological and individual factors, including resilience some