What Causes Mental Illness? Genetics, Environment, Risk Factors

What causes mental illness? Is mental illness hereditary? Is mental illness genetic? Get answers plus the risk factors in mental illness. Read this.

What causes mental illness? The question is a crucial one, for knowing the causes of mental illness aids in both prevention and mental health treatment. However, the answer to that key question is still being researched. As scientists in the field of psychology and mental health look deeper into the causes of mental illness, they're turning their attention to things like genetics and the environment as both causes and risk factors.

Regarding mental illness causes, much is still a mystery. However, there are certain truths that are known with certainty:

Many Factors Cause Mental Illness

The development of mental illness is rarely if ever caused by a single factor. The major forces at work, the main focus of researchers when they look into the causes of mental illness, include:

  • biology (neurochemistry, brain structure, and genetics)
  • environment
  • lifestyle
  • the combination of and interaction between these

What Causes Mental Illness? Biology, Genetics

Is mental illness hereditary? Is mental illness genetic? These common questions about the biological nature of mental illness don't have a simple answer.

Studies of identical twins and of mentally ill parents and their children (Mental Illness in Children: Types, Symptoms, Treatments) indicate that there is indeed a genetic component to mental illness. However, it's inaccurate to say that mental illness is hereditary. For a trait to be hereditary, it must be passed directly from one generation to the next (or, in some cases, from a grandparent to grandchild). Characteristics like male pattern baldness and eye color are hereditary. While mental illness often runs in families, mental illness is not hereditary.

Mental illness is heritable. This means that people don't inherit mental illness; rather, they inherit genes that make them susceptible to mental illness. Mental illness isn't a trait, so it can't be passed down directly from parent to child. The genes that have the potential to activate mental illness can be passed from parent to child, so mental illness is indeed genetic.

The brain itself can also be a cause of mental illness. Its structure and neurochemistry—neurochemicals and other molecules in the brain—can make it vulnerable to the development of mental illness. Traumatic brain injury, too, can be a cause of mental illness.

What Causes Mental Illness? Environment, Lifestyle

To answer the question of what causes mental illness, researchers also turn to the environment, the world in which someone lives and functions. Environmental causes are causes external to the person. This is a broad category whose list is extensive. Just a few examples are

  • chronic stressors, such as economic hardship or social struggles
  • low quality of life, due to poverty or a feeling of dissatisfaction with one's life
  • trauma
  • exposure to toxins, especially at certain developmental stages
  • family and/or relationships problems
  • child abuse
  • lifestyle considerations like substance use and risk-taking

To be sure, extreme adversity in one's environment can be a cause or contributing factor to mental illness. Still, the picture is complex. Take posttraumatic stress disorder (PTSD), for example. To develop PTSD, someone must experience, either directly or vicariously, a trauma, and the person must be biologically/genetically predisposed to developing PTSD. Otherwise, everyone exposed to trauma would develop PTSD, and this isn't the case.

Risk Factors of Mental Illness

Generally, risk factors are those things that make someone vulnerable to developing mental illness. Because they're similar in nature to the causes of mental illness, it's hard to differentiate between things that increase someone's risk for developing mental illness and things that cause mental illness to develop.

A list of risk factors is similar to a list of causes or contributing factors. Often, looking at a diagnosis of mental illness, causes, and risk factors will reveal that assigning a cause or identifying a risk factor is a matter of the chicken and the egg. Which comes first? Perhaps it doesn't deeply matter.

All of the different causes of mental illness—biological and genetic causes and the wide variety of environmental causes—plus the very similar risk factors dance together in a complex motion to lead to the diagnosis of a specific mental illness.

APA Reference
Peterson, T. (2018, October 23). What Causes Mental Illness? Genetics, Environment, Risk Factors, HealthyPlace. Retrieved on 2024, July 24 from

Last Updated: October 23, 2019

Medically reviewed by Harry Croft, MD

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