Abnormal behavior, often referred to as mental illness, results from changes in brain function that influence thought patterns, behaviors, and social interactions. Psychologists and psychiatrists typically assess abnormal behavior using three primary criteria: deviance, maladaptation, and personal distress, particularly when these traits persist over long periods.

Deviant Behavior
Deviance in behavior refers to actions or thought patterns that significantly diverge from societal norms or statistical averages. These behaviors are considered atypical within a cultural or social context. For example, someone who repeatedly checks their locks every few minutes exhibits a pattern that departs significantly from typical behavior. Although such repetitive actions may be intended to provide reassurance, they could stem from underlying anxieties or obsessive-compulsive tendencies, indicating a substantial departure from cultural expectations.

Maladaptive Behavior
Maladaptive behavior impairs an individual's ability to adapt to everyday demands, often disrupting normal functioning effectively. This type of behavior can include compulsive actions that lead to inefficiencies and increased stress. For instance, a person who avoids stepping on pavement cracks to prevent imagined misfortune may take a longer route, resulting in significant delays. While these behaviors may seem harmless, they can interfere with punctuality for work or social commitments, impairing daily functionality and diminishing overall quality of life.

Personally Distressful Behavior
Behaviors that cause ongoing emotional distress reflect an internal struggle beyond occasional discomfort. Individuals experiencing such behaviors may endure persistent anxiety, self-criticism, or other negative emotional states. For example, someone who severely restricts their food intake due to an intense fear of weight gain may constantly struggle with body image issues, leading to chronic anxiety and harmful self-perception. Such prolonged distress is often associated with disorders like anorexia nervosa, where restrictive eating patterns dominate the individual's life.