What Is a Mental Illness?

Definition of mental illness plus the five major categories of mental illness and misconceptions about mental illness.

Definition of mental illness plus the five major categories of mental illness and misconceptions about mental illness.

A mental illness is a disease that causes mild to severe disturbances in thinking, perception and behavior. If these disturbances significantly impair a person's ability to cope with life's ordinary demands and routines, then he or she should immediately seek proper treatment with a mental health professional. With proper care and treatment, a person can recover and resume normal activities.

Many mental illnesses are believed to have biological causes, just like cancer, diabetes and heart disease, but some mental disorders are caused by a person's environment and experiences.

The five major categories of mental illness:

Anxiety Disorders

Anxiety disorders are the most common mental illnesses. The three main types are phobias, panic disorders, and obsessive-compulsive disorder. People who suffer from phobias experience extreme fear or dread from a particular object or situation. Panic disorders involve sudden, intense feelings of terror for no apparent reason and symptoms similar to a heart attack. People with obsessive-compulsive disorder try to cope with anxiety by repeating words or phrases or engaging in repetitive, ritualistic behavior such as constant hand washing.

Mood Disorders

Mood disorders include depression and bipolar disorder (or manic depression) symptoms may include mood swings such as extreme sadness or elation, sleep and eating disturbances, and changes in activity and energy levels. Suicide may be a risk with these disorders.


Schizophrenia is a serious disorder that affects how a person thinks, feels, and acts. Schizophrenia is believed to be caused by chemical imbalances in the brain that produce a variety of symptoms including hallucinations, delusions, withdrawal, incoherent speech and impaired reasoning.


This group of disorders includes diseases like Alzheimer's which leads to loss of mental functions, including memory loss and a decline in intellectual and physical skills.

Eating Disorders

Anorexia nervosa, binge eating disorder, and bulimia are serious, potentially life-threatening illnesses. People with these disorders have a preoccupation with food and irrational fear of being fat. Anorexia is self-starvation while bulimia involves cycles of bingeing (consuming large quantities of food) and purging (self-inducing vomiting or abusing laxatives). Behavior may also include excessive exercise. 

Common Misconceptions About Mental Illness

Myth: "Young people and children don't suffer from mental health problems."

Fact: It is estimated that more than 6 million young people in America may suffer from a mental health disorder that severely disrupts their ability to function at home, in school, or in their community.

Myth: "People who need psychiatric care should be locked away in institutions."

Fact: Today, most people can lead productive lives within their communities thanks to a variety of supports, programs, and/or medications.

Myth: "A person who has had a mental illness can never be normal."

Fact: People with mental illnesses can recover and resume normal activities. For example, Mike Wallace of "60 Minutes," who has clinical depression, has received treatment and today leads an enriched and accomplished life.

Myth: "Mentally ill persons are dangerous.

Fact: The vast majority of people with mental illnesses are not violent. In the cases when violence does occur, the incidence typically results from the same reasons as with the general public such as feeling threatened or excessive use of alcohol and/or drugs.

Myth: "People with mental illnesses can work low-level jobs but aren't suited for really important or responsible positions."

Fact: People with mental illnesses, like everyone else, have the potential to work at any level depending on their own abilities, experience and motivation.

How You Can Combat Stigma:

1. Share your experience with mental illness. Your story can convey to others that having a mental illness is nothing to be embarrassed about.

2. Help people with mental illness re-enter society. Support their efforts to obtain housing and jobs.

3. Respond to false statements about mental illness or people with mental illnesses. Many people have wrong and damaging ideas on the subject. Accurate facts and information may help change both their ideas and actions.

For More Information:

Contact your local Mental Health Association, community mental health center, or for additional resources, please call 1-800-969-NMHA.

NMHA offers additional pamphlets on a variety of mental health topics. For more information or to order multiple copies of pamphlets, please call 1-800-969-NMHA

Source: Mental Health America

APA Reference
Writer, H. (2009, January 6). What Is a Mental Illness?, HealthyPlace. Retrieved on 2019, August 25 from

Last Updated: July 2, 2019

Medically reviewed by Harry Croft, MD

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