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Although the exact cause of most mental illnesses is not known, it is becoming clear through research that many of these conditions are caused by a combination of biological, psychological, and environmental factors.




Some mental illnesses have been linked to an abnormal balance of special chemicals in the brain called neurotransmitters. Neurotransmitters help nerve cells in the brain communicate with each other. If these chemicals are out of balance or are not working properly, messages may not make it through the brain correctly, leading to symptoms of mental illness.


  • Genetics (heredity): Many mental illnesses run in families, suggesting that people who have a family member with a mental illness are more susceptible to developing a mental illness. Susceptibility is passed on in families through genes. Experts believe many mental illnesses are linked to abnormalities in many genes, not just one. That is why a person inherits a susceptibility to a mental illness and doesn't necessarily develop the illness. Mental illness itself occurs from the interaction of multiple genes and other factors such as stress, abuse, or a traumatic event, which can influence or trigger an illness in a person who has an inherited susceptibility to it. 

  • Infections: Certain infections have been linked to brain damage and the development of mental illness or the worsening of its symptoms. For example, a condition known as pediatric autoimmune neuropsychiatric disorder (PANDA) associated with the Streptococcus (Strep) bacteria has been linked to the development of obsessive-compulsive disorder and other mental illnesses in children.  Brain defects or injury: Defects in or injuries to certain areas of the brain have also been linked to some mental illnesses. 

  • Prenatal damage: Some evidence suggests that a disruption of early fetal brain development or trauma that occurs at the time of birth, for example, loss of oxygen to the brain, may be a factor in the development of certain conditions, such as autism.

  • Other factors: Poor nutrition and exposure to toxins, such as lead, may play a role in the development of mental illnesses.



  • Severe psychological trauma suffered as a child, such as emotional, physical, or sexual abuse

  • An important early loss, such as the loss of a parent

  • Neglect

  • Poor ability to relate to others



  • A dysfunctional family life

  • Living in poverty

  • Significant life changes 

  • Social or cultural expectations

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