A mental disorder or mental illness is a psychological or behavioral pattern generally associated with subjective distress or disability that occurs in an individual, and which is not a part of normal development or culture. Such a disorder may consist of a combination of affective, behavioral, cognitive and perceptual components.
The recognition and understanding of mental health conditions have changed over time and across cultures, and there are still variations in the definition, assessment, and classification of mental disorders, although standard guideline criteria are widely accepted. A few mental disorders are diagnosed based on the harm to others, regardless of the subject’s perception of distress. Over a third of people in most countries report meeting criteria for the major categories at some point in their lives.
The causes are often explained in terms of a diathesis-stress model or bio psycho social model. In biological psychiatry, mental disorders are conceptualized as disorders of brain circuits likely caused by developmental processes shaped by a complex interplay of genetics and experience.