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What Causes Mental Illness?

Katelyn Brenner FNP

Reviewed by Katelyn Hagerty FNP

Written by Geoffrey Whittaker

Published 12/07/2021

Updated 12/08/2021

It’s safe to say that life can be stressful and, at times, overwhelming. While everyone has days where you dread getting out of bed in the morning, for many, this reality is not just a passing phase. 

When intrusive thoughts or behaviors start to make it difficult to do simple tasks, perform at your job or make meaningful connections with friends and family, you might be experiencing mental illness.

Unfortunately, mental illness, if left untreated, can profoundly affect your quality of life. 

If you’ve been diagnosed with a mental illness or are in the early stages of researching if you have one, know that you are not alone and there is hope. Mental illness is no one’s fault, but the first step to recovery is to learn more about what causes mental illness in the first place, and what you can do to process and overcome it.

Mental illness is a medical condition that affects a person’s thoughts, mood or behavior. Your personal experiences, lifestyle and genetics all play a role in the way you see yourself. They also play a role in how you connect with the world around you. 

So, having a stressful home life, working in a toxic environment or experiencing a traumatic life event can make you more susceptible to developing a mental illness. 

Your individual brain chemistry is something that you have little to no control over, and yet it’s a major factor in your ability to positively process the experiences you have day to day.

It’s also a determining element in how you relate to others, and whether you do so in a healthy, positive way.

Unfortunately, when your thoughts, mood and behavior are influenced by mental illness, that illness can have a profound impact on your life and can make it difficult for you to engage in society and to form healthy relationships with others.

Despite what you may have been told, mental illness is common. A reported one in five U.S. adults experience some form of mental illness each year. 

Surprised? Here are some additional statistics about mental illness you might find interesting:

  • One in six young people between ages six and 17 will experience a mental health disorder each year.

  • Fifty percent of mental illnesses begin by age 14, and 75 percent by age twenty-four.

What are mental health risk factors you can look out for? Multiple extrinsic and intrinsic factors — often in combination — can lead to a diagnosis for mental illness, which means that your biological factors and environmental factors can both increase your risk.

Extrinsic factors that impact mental health are environmental or experiential, such as job stress, a traumatic life event, consuming drugs or alcohol or having a history of abuse or neglect. 

It can also include damage the brain may incur from events like a traumatic injury or even exposure to toxic chemicals or viruses while in the womb.

Intrinsic factors are innate and therefore more difficult to control, including your biochemical processes and genetic makeup. 

Anomalies in your brain chemistry may lead to impaired neural networks that limit the function of nerve receptors to support healthy brain function, causing mood disorders. 

This can in turn lead to negative thoughts or unhealthy habits like loss of sleep, which can be difficult to manage without an effective behavioral or medical coping strategy.

In addition to the causes listed above, there are factors that will exacerbate a person’s mental illness. 

A person’s support system, as well as socio-economic factors, play big roles in the potential duration and severity of their mental illness. 

Financial issues including poverty, homelessness or legal troubles create an unstable environment that make it difficult to sustain positive mental health. 

Similarly, feelings of isolation from a lack of friends, or experiencing toxic friends or relationships in your life can add to the strain of a mental illness.

It’s worth noting that these are just a few of many examples of things that might exacerbate mental health issues. 

Treating a mood disorder or other mental illness isn’t an easy process. In fact most people are never really “cured,” so much as they find an effective treatment to manage their condition. 

The best way to treat mental health conditions is on a case-by-case basis, with one or more treatment options that may include:

Practicing self-care

Sleeping and eating well, as well as exercising regularly and making other smart lifestyle choices are important components to leading a healthy lifestyle. 

Maintaining a routine can help break negative thought and behavioral patterns and lead to an overall improvement in your mental health.

Engaging in routine medical care

Always stay on top of your checkups and remember to talk to your healthcare provider if you have difficulty sleeping or want to learn more about diet or exercise routines that will suit your needs. 

It’s also possible to have a physical illness that could cause negative mental health symptoms.

Connecting with others

Humans are social creatures, and we all get by with a little help from friends and family. 

Forming relationships with others and maintaining a healthy support system can help you lead a more healthy and fulfilling lifestyle. 

If you’re struggling, don’t hesitate to reach out to your network for help.

Seeking professional help

When you’re having difficulty coping on your own, there are mental health professionals who can provide you with comprehensive care including therapy, individual or group counseling and medications to help you manage your mental illness. 

For more severe cases, a visit to a residential treatment program or psychiatric hospital may be a necessary respite to focus on improving your mental health.

“Mental illness” is a broad term that covers a variety of conditions that impact mood and behavior. 

These may be classified as a mood disorder or emotional disorder — mental illness can go by many names. Here are the most common forms of mental illness:

Anxiety Disorder

Though everyone experiences a case of nerves from time to time, someone can be characterized as having an anxiety disorder when they are consistently afraid of situations which are non-threatening.

These situations include things like talking to a cashier in a grocery store or ordering in a restaurant. 

Anxiety disorder is the most common mental illness in the US, with over 40 million people (19.1 percent) reporting symptoms. 

Attention-Deficit/Hyperactivity Disorder (ADHD)

Commonly associated with overly hyperactive children, ADHD can manifest in adulthood, as well. 

Difficulty focusing, impulsivity and fidgeting are all hallmarks of this disorder, which although manageable, can in certain contexts provide significant challenges to the demands of everyday life.

Bipolar Disorder

People with bipolar disorder, as the name suggests, experience low and high moods intensely on opposite poles: depression and mania. 

In a depressed state, a person with this disorder becomes lethargic and easily overwhelmed with daily tasks. 

While in a manic state, their mood elevates to an unsustainable high that devolves into unpredictability and irritability at best, and delusional, destructive behavior at worst.

Borderline Personality Disorder (BPD)

More often diagnosed in women, people with BPD experience intense feelings and have difficulty regulating their emotion, leading to unstable relationships and impulsive, self-destructive behavior. 

Recent research suggests that more men may have BPD than previously thought, having been misdiagnosed with another disorder such as PTSD.


Feeling down or struggling through a tough time is one thing, but you can start to label that feeling “depression” when these feelings last for more than two weeks. 

Losing interest in activities or food, inability to sleep and loss of energy and motivation are some of the hallmarks of a depressive disorder. 

In severe cases, depression can manifest in physical symptoms or lead to suicidal thoughts.

Dissociative Disorder

Often a result of experiencing a traumatic event, dissociative order causes you to involuntarily escape from reality. 

These episodes cause memory loss, lead to detachment and can create a sense of lost identity. 

Treatment for dissociative disorders typically involves both psychotherapy and medication.

Eating Disorders

When food becomes an object of obsession in your life, you might have an eating disorder. 

Losing control over your relationship to food can come in several forms. People with anorexia nervosa deny food to achieve unattainable weight loss goals, while sufferers of bulimia nervosa and binge eating disorder self-soothe with food and find it impossible to stop.

Obsessive-Compulsive Disorder (OCD)

It’s become a cliche to say “I have OCD” if you happen to get irked by crooked picture frames, but the reality of OCD is more harmful. 

People with this disorder have irrational thoughts that they are unable to control and that interfere with their daily life. 

They may perform a ritual like hand-washing multiple times in a row, just to relieve their anxiety.

Post-traumatic Stress Disorder

As its name indicates, post-traumatic stress disorder is an involuntary response to a traumatic event.

In the case of an assault for example, the victim may have difficulties actively remembering the incident, but then experience intrusive recurring thoughts or memories of the event at other times, creating a “fight-or-flight” bodily response.


The concept of the “psycho” in pop culture doesn’t accurately convey what “psychosis” is in the clinical sense. 

Psychosis is actually a symptom rather than a disorder, which causes a person to experience disruptions to their thoughts and perceptions that confuse their sense of reality. 

It’s also more common than you may think, with 100,000 young adults experiencing a psychotic episode each year in the U.S., and three percent of people experiencing one over the course of their lifetime.


Schizophrenia is a complicated and long-term mental illness that severely interferes with a person’s ability to make decisions and form healthy relationships with others. 

While it can be difficult to diagnose, some symptoms include hallucinations and disorganized thoughts or speech. 

Diagnosing schizophrenia early on increases a person’s ability to manage the illness and reduce the psychotic episodes they experience.

Schizoaffective Disorder

Schizoaffective disorder combines symptoms of schizophrenia, such as delusions, with symptoms of a mood disorder, such as mania or depression. 

Since it manifests as a combination of symptoms from other disorders, it is often misdiagnosed.

Whether suffering from a mental illness is affecting your ability to complete your daily activities today or not, you should definitely address signs that you may have a mental health condition with a mental health profession tomorrow. 

Emotional disorders like anxiety and depression and everything else we discussed here should be addressed by a treatment plan created by a therapy professional.

Left untreated, these common disorders can prevent you from enjoying everything from social activities to relationships — there are just too many reasons to get help now. 

A diagnosis will be the first task, and once you know that you have severe depression or generalized anxiety disorder or seasonal affective disorder (or something else!), a mental health professional can help you combat the negative symptoms to prevent harm to your physical health, social isolation and everything else that can come from untreated mental illness.

14 Sources

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  2. “Mental Illness.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 8 June 2019,
  3. “Mental Health Conditions.” NAMI,
  4. “Mental Disorders.” MedlinePlus, U.S. National Library of Medicine, 12 Oct. 2021,
  5. “Schizoaffective Disorder.” NAMI,
  6. “Schizophrenia.” NAMI,
  7. “Eating Disorders.” NAMI,
  8. “Posttraumatic Stress Disorder.” NAMI,
  9. “Psychosis.” NAMI,
  10. “ADHD.” NAMI,
  11. “Depression.” NAMI,
  12. “Borderline Personality Disorder.” NAMI,
  13. “Bipolar Disorder.” NAMI,
  14. “Dissociative Disorders.” NAMI,
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