Causes of Mental Illness

Written by Martha Anne Tudor
Medically Reviewed by Smitha Bhandari, MD on March 06, 2025
5 min read

What causes mental illness? It's complicated. Although the exact origin of most mental illnesses isn't known, research shows they often come from a complex mix of biological, genetic, psychological, socioeconomic, and environmental factors.

Some mental illnesses run in families. But that doesn't mean you'll have one just because your mother or father does.

There are certain mental health conditions that involve circuits in your brain used in thinking, mood, and behavior. Brain injuries are also linked to some mental conditions.

Mental illnesses can also 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

The risk for mental illness is higher for certain groups of people, regardless of their age. Those include the LGBTQ community, people with disabilities, those who are socially isolated, and people who've experienced loss, inequality, violence, homelessness, addiction, or abuse.

Major sources of stress, such as the death of a loved one, divorce, problems in your family relationships, job loss, school, and substance abuse can trigger or worsen mental disorders you already live with. But not everyone who goes through those challenges has issues with mental health.

It's normal to feel grief, anger, and other emotions when there's a major setback in your life. But mental illness is different than that.

Whether your feelings are normal responses or a sign of possible mental illness depends on many factors. They include how intense, persistent, or disruptive your feelings are. If your feelings last long after an event and they keep you from moving forward with your life, it's time to seek mental health help.

Some mental illnesses are linked to abnormal functioning of nerve cell circuits or pathways that connect particular regions of your brain. Nerve cells in these brain circuits use chemicals called neurotransmitters to send messages. "Tweaking" these chemicals — through medicines, psychotherapy, or other medical treatments — can help your brain circuits run more efficiently. In addition, defects in, or injury to, certain areas of your brain are also linked to some mental health conditions.

Other biological factors that might play a role in mental illness include:

Genetics (heredity). Mental illnesses sometimes run in families. If you have a family member with a mental illness, you could be more likely to have that. This risk is passed down through genes you inherit from your parents. Experts believe some mental illnesses are linked to abnormalities in many genes, rather than just one or a few. They believe the ways your genes interact with your environment are different for every person (even identical twins raised in the same home). That's why you can inherit a tendency for mental illness but not have it. Mental illness comes from the interaction of multiple genes and various other factors — such as stress, abuse, or a traumatic event.

Infections. Certain infections have been linked to brain damage and the development of mental illness or the worsening of mental illness symptoms. For example, a condition known as pediatric autoimmune neuropsychiatric disorder (PANDAS) linked to the streptococcus bacteria can be linked to obsessive-compulsive disorder (OCD) and other mental health conditions in children.

Brain defects or injury. Defects in or injury to certain areas of your brain are linked to some mental illnesses.

Prenatal damage. Some evidence suggests that problems in early fetal brain development or trauma during birth — for example, loss of oxygen to your brain — may increase your risk of mental health conditions such as autism spectrum disorder.

Substance abuse. Long-term substance abuse has been linked to mental health conditions including anxiety, depression, and paranoia.

Chronic health conditions. Many chronic medical problems, such as diabetes and epilepsy, raise your risk for mental health issues.

Other factors. Poor nutrition and exposure to toxins, such as lead, may make you more likely to get a mental illness.

Many psychological factors may lead to mental illness. Some include:

  • Trauma experienced as a child, such as emotional, physical, or sexual abuse
  • Significant loss early in life, such as the loss of a parent
  • Neglect
  • Poor ability to relate to others
  • Discrimination or stigma
  • Lack of healthy relationships

Certain stressors can trigger mental illness. They include:

  • Death of a loved one
  • 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, associating beauty with thinness may play a role in developing eating disorders)
  • Substance abuse by you or your parents
  • Financial problems
  • Work or career stress
  • Social isolation
  • Domestic violence
  • Natural disasters

Research continues to show a link between social and economic inequality and poor mental health. This seems to affect adults as well as children and adolescents, including immigrants. Socioeconomic factors that lead to mental illness include:

  • Unemployment
  • Low income
  • Poverty
  • Debt
  • Homelessness
  • Low or no education
  • Asylum status
  • Displaced person status
  • Refugee status

Socioeconomic factors are often linked to environmental factors.

What is the root cause of mental illness?

Mental illnesses can have multiple causes, including genetic, biological, psychological, socioeconomic, and environmental factors. Life experiences also play a big role.

Can lack of sleep cause mental illness?

Yes. Lack of sleep can lead to mental illnesses, including depression and anxiety. Not getting enough sleep can also raise your risk of suicide. If you or someone you know is having thoughts of self-harm or suicide, help is available any time day or night. Call or text the 988 Suicide and Crisis Lifeline.

Can something trigger a mental illness?

Yes. If you have a very stressful life event or situation, it can trigger mental illness or make existing mental illness worse. Triggers are different for different people, depending on your experiences and past trauma. What triggers one person might not affect someone else. Triggers are more likely to start or worsen mental illness if you're predisposed to it. That's because mental illness often stems from a combination of genetic, environmental, and other factors.