APA Dictionary of Psychology

a theoretical construct proposing that stable personality types and coping styles (e.g., chronic stress reactivity, maladaptive emotion regulation, hostility, pessimism) increase an individual’s vulnerability to physical illness, particularly coronary heart disease and cancer, by influencing physiological stress responses, health behaviors, and immune or endocrine functioning. The concept was historically influential but controversial, with current research emphasizing specific, measurable traits and mechanisms (e.g., stress appraisal, coping, allostatic load) rather than a single, disease-prone personality type. See also Type A personality.