This detailed answer explains various aspects of emotion, including its components, theories, and effects on the body and the immune system.
Emotions involve subjective labeling, behavioral, and cognitive components, and the process of emotion includes subjective experience, expression, cognitive appraisal, and physiological responses (Levenson, Carstensen, Friesen, & Ekman, 1991). Joy, anger, fear, and disgust are part of the core emotions. The theory of emotion that says we "label" an emotion because of our cognitive appraisal of a situation comes from Lazarus's cognitive-mediational theory and the Schachter-Singer two-factor theory. Charles Darwin believed that many of our emotional expressions are universal traits. Scientific research shows that experimental inducing participants to smile had them reporting more positive emotions. Opponent process theories of emotions explain the contrasting emotions experienced after the initial emotion, and Hans Seyle's term for the body's three-stage response to stress is the General Adaptation Syndrome. Stressful situations tend to result in increased heart rate and blood pressure, and stress affects the immune system by weakening it. Type A and Type B descriptions of people differ in terms of personality traits and responses to stress. Two Type A traits that play an especially important role in coronary heart disease are time urgency and expression of aggression.