Causes of Mental Illness

Medically Reviewed by Poonam Sachdev on March 28, 2023
4 min read

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.

Many mental illnesses run in families. But that doesn’t mean you will have one if your mother or father did.

Some conditions involve circuits in your brain that are used in thinking, mood, and behavior. For instance, you may have too much, or not enough, activity of certain brain chemicals called neurotransmitters within those circuits. Brain injuries are also linked to some mental conditions.

Some mental illnesses may be triggered or worsened by psychological trauma that happens when you’re a child or teenager, such as:

  • Severe emotional, physical, or sexual abuse
  • A major loss, such as the death of a parent, early in life
  • Neglect

Major sources of stress, such as a death or divorce, problems in family relationships, job loss, school, and substance abuse, can trigger or aggravate some mental disorders in some people. But not everyone who goes through those things gets a mental illness.

It’s normal to have some grief, anger, and other emotions when you have a major setback in life. A mental illness is different from that.

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 treatments – 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 have one themselves. This susceptibility is passed on in families through genes. Experts believe that 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 likeliness to have a mental illness and doesn't necessarily get the illness. Mental illness itself comes 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 likeliness to have 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 (PANDAS) 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 play a part in certain conditions, such as autism spectrum disorder.
  • 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 mental illnesses.

Psychological factors that may contribute to mental illness include:

  • 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

Certain stressors can trigger an illness in a person who is more likely to have mental illness. These stressors include:

  • Death or divorce
  • A dysfunctional family life
  • Feelings of inadequacy, low self-esteem, anxiety, anger, or loneliness
  • Changing jobs or schools
  • Social or cultural expectations (For example, a society that associates beauty with thinness can be a factor in the development of eating disorders.)
  • Substance abuse by the person or the person's parents



Research continues to show a link between social and economic inequality and poor mental health. Adults and children/adolescents alike seem to be affected, along with immigrants. Socioeconomic factors that contribute to mental illness include:

  • Unemployment 
  • Low income 
  • Poverty  
  • Debt 
  • Poor or unstable living conditions
  • Education 

Socioeconomic factors are often connected to environmental factors.