Mental illness is a term used to describe significant disturbances in thought, mood or behavior that cause patients to have difficulty functioning psychologically. Patients may have difficulty interacting with others in social settings, performing efficiently on the job or at school, forging strong relationships or carrying out other aspects of day-to-day life.

There are many different formally recognized types of mental illness. Approximately 54 million people in the United States experience some form of mental illness annually, according to the National Mental Health Association.

Mental illnesses are classified according to the symptoms that a patient experiences, as well as the clinical features of the illness. Some of the major categories of mental illness include anxiety disorders, cognitive disorders, developmental disorders, dissociative disorders, mood disorders, personality disorders, schizophrenia and substance abuse disorders.

Although many mental illnesses are chronic, others are cyclical (e.g., seasonal affective disorder) or temporary (e.g., postpartum depression) in duration.

There are many different potential causes of mental illness. Some people are born with genetic factors or chemical imbalances that make them more likely than others to develop a particular mental condition. Risk factors other than biology, such as a traumatic event or environmental stress, can also trigger mental illness. In some cases, the cause of a particular mental illness is unknown. However, researchers are currently working to identify factors that contribute to these conditions.

The signs and symptoms of mental illness vary significantly in both nature and severity depending on the individual and the condition that is present. Some are obvious, whereas others are more subtle. In diagnosing a mental illness, a physician or a non-physician mental health professional will note these signs and symptoms, as well as any impairment in occupation or social functioning that is present.

Psychotherapy, medications or a combination of both are often used to treat symptoms associated with mental illness. Many mental illnesses cannot be prevented. However, some symptoms can be prevented or managed before they worsen by taking steps such as trying to remain positive about life circumstances, learning and using problem-solving skills that can help one cope with life’s challenges, and discussing concerns and difficulties with trusted family members and friends.