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Anxiety & Panic Disorders Health Center

Causes of Mental Illness

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What are the causes of mental illness? 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.

What Biological Factors Are Involved in Mental Illness?

Some mental illnesses have been linked to abnormal functioning of nerve cell circuits or pathways that connect particular brain regions. Nerve cells within these brain circuits communicate through chemicals called neurotransmitters. "Tweaking" these chemicals -- through medicines, psychotherapy or other medical procedures -- can help brain circuits run more efficiently. In addition, defects in or injury to certain areas of the brain have also been linked to some mental conditions.

Other biological factors that may be involved in the development of mental illness include:

  • Genetics (heredity): Mental illnesses sometimes run in families, suggesting that people who have a family member with a mental illness may be somewhat more likely to develop one themselves. Susceptibility is passed on in families through genes. Experts believe many mental illnesses are linked to abnormalities in many genes rather than just one or a few and that how these genes interact with the environment is unique for every person (even identical twins). 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 bacteria has been linked to the development of obsessive-compulsive disorder and other mental illnesses in children.
  • Brain defects or injury: Defects in or injury 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.
  • Substance abuse: Long-term substance abuse, in particular, has been linked to anxiety, depression, and paranoia. 
  • Other factors: Poor nutrition and exposure to toxins, such as lead, may play a role in the development of mental illnesses.

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