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  • Writer's pictureKim WD, Psych NP

What Causes Mental Illness?

Wouldn't it be convenient if we could trace the appearance of a mental illness (or mental health disorder) to a specific event, chemical, personality type, or other illness? Unfortunately, it will never be that simple.

Most mental illnesses are the end result of not one but many factors, each contributing in ways both expected and unexpected. While we are not able to pinpoint the root cause of most mental illnesses, we are beginning to learn how different statuses and situations can increase our risk factors for developing a mental health disorder. Keep reading for a short review of some of the best known ones.


Genetics. Mental illness can run in families. If one first-degree relative (i.e., parent, sibling, child) has a mental illness, other family members are at an increased risk of developing a mental illness at some point in their lives. A person’s genetic risk for developing a mental health disorder is also dependent on the type of mental illness. So, how much of a role does genetics play in different mental illnesses?

  • Depression: 25-40% of cases have a genetic contributor.

  • ADHD: 50-75% of cases have a genetic contributor.

  • Bipolar disorder: 65-75% of cases have a genetic contributor.

  • Schizophrenia: 70-80% of cases have a genetic contributor.

Brain chemistry. Your brain uses chemical messengers called neurotransmitters to communicate with other parts of your brain and body. For many people, neurotransmitters do their job well and smoothly. But for some people, the chemical messenger system is glitchy, and their neurotransmitters are not doing their jobs effectively. Differences in neurotransmitter function in the brain (creation or transmission) may contribute to symptoms of mental illness. “May contribute,” however, does not mean “definitely causes.”

When neurotransmitters aren’t working right (too much, not enough, or not reaching their destinations), it is sometimes possible to give them a hand with a neurotransmitter-targeted medication.


A person’s personality can be a contributing factor in the development of a mental illness. People who have persistent, hard to control feelings of anxiety or obsessional thoughts, who engage in compulsive or impulsive acts, and/or have multiple physical complaints (that are not traceable to verifiable physical health issues) are more likely to develop mental health disorders. Other personality traits and tendencies that are linked to mental illness include:

  • Chronic excessive anxiety or indecision

  • High level of social or interpersonal dysfunction

  • Low self-esteem

  • Easily overwhelmed by stress

  • Chronically irritable, chronically angry, chronically blowing up

  • Prone to a negative outlook (pessimistic)


Trauma. Continual exposure to trauma (including cultural or familial violence, neglect, abuse, or poverty) may make some people more vulnerable to mental illness. Resilience (the ability to bounce back or overcome) is a protective factor.

Adverse childhood events (collectively referred to as ACE) are traumatic events that can add up. According to the CDC, adverse childhood events can include violence, abuse, and growing up in a family with mental health or substance use problems. Toxic stress from ACEs can change brain development and affect how the body responds to stress in the future. ACEs are linked to chronic health problems, mental illness, and substance misuse in adulthood. The more adverse childhood events that a child is exposed to (i.e., the higher their ACE score), the higher the likelihood that that child will be affected by mental health or substance use issues later in life.

Injury. While any injury can contribute to stress, a traumatic brain injury (TBI) ups the ante and can increase the risk of developing a mental illness by up to 50%, with depression being the most common. Vulnerability to mental illness can persist for decades after such an injury.

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disorder that results from repetitive brain injuries over a long period of time. Childhood sports participants (e.g., soccer, basketball, football) and domestic abuse victims are the primary populations at risk for CTE. CTE has been linked to a number of serious psychiatric symptoms, including depression, aggression, and suicidal thoughts and behavior.

Stress. Experiencing acute or chronic stress can have a major impact on mental health. Stress can disrupt brain function, which in turn may result in the loss of sociability and the avoidance of interactions with others. In recent studies, stress has been shown to kill brain cells, and in some instances even reduce the size of the brain. And we’re not just talking about acute, extreme, or traumatic stress – lower levels of chronic, ongoing stress can also cause damage to the brain and raise the risks for mental health disorders.

Chronic stress can affect emotional balance and mental health, and it can also shrink the area of the brain responsible for memory and learning. When you experience stress, your body puts out stress hormones, including adrenaline and cortisol. Excesses of stress hormones can disrupt almost all your body's processes. When this happens, you are at increased risk of many health problems, including –

  • Anxiety

  • Depression

  • Digestive problems

  • Headaches

  • Heart disease

  • Sleep problems

  • Weight gain

  • Memory and concentration impairment


Making healthy choices. It should go without saying, but making healthy choices (diet, exercise, sleep, and so on) can lower your risks for both physical and mental health problems. Studies have shown that some ways to head off mental health issues (and maintain a higher level of life satisfaction) include –

  • Maintaining a lower body mass index (BMI),

  • Engaging in more frequent physical and mental activities,

  • Not smoking (which includes vaping),

  • Limiting alcohol consumption,

  • Avoiding the use of illegal, street, and illicit drugs and other chemicals,

  • Getting enough sleep,

  • Not following a strict vegetarian or vegan diet (protein is brain food, and high quality protein is required for good brain function), and

  • Maintaining a regular social life!


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