Emotions evolved to bind people together, motivate them to achieve their goals, and help them make decisions and plans. The experience of emotion involves physiological changes, cognitive processes, action tendencies, and subjective feelings. Some facial expressions—anger, fear, sadness, happiness, disgust, surprise, contempt, and possibly pride—are widely recognized across cultures. But an accurate reading of others' facial expressions increases among members of the same ethnicity, and depends on the social context. Also, because people can and do disguise their emotions, their expressions do not always communicate accurately.

The amygdala is responsible for initially evaluating the emotional importance of incoming sensory information and is especially involved in fear. The cerebral cortex provides the cognitive ability to override this initial appraisal. Regions of the left prefrontal cortex appear to be specialized for the motivation to approach others (as with happiness and anger), whereas regions of the right prefrontal region are specialized for withdrawal or escape (as with disgust and fear). Mirror neurons throughout the brain are activated when people observe others, especially other people of the same group or others they like. These neurons seem to be involved in empathy, imitation, synchrony, and mood contagion. During the experience of any emotion, epinephrine and norepinephrine produce a state of physiological arousal to prepare the body for an output of energy.

Cognitive approaches to emotion emphasize the perceptions and appraisals that are involved in different emotions. Thoughts and emotions operate reciprocally, each influencing the other. Some emotions, such as shame and guilt, require complex cognitive capacities.

Many psychologists believe that all human beings share the ability to experience certain basic emotions. However, cultural differences in values, norms, and appraisals generate emotion blends and culture-specific emotional feelings. Culture affects almost every aspect of emotional experience, including which emotions are considered appropriate or wrong, and what people feel emotional about.

Culture strongly influences display rules, including those governing nonverbal body language, that regulate how and whether people express their emotions. Emotion work is the effort a person makes to display an emotion he or she does not feel but feels obliged to convey.

Women and men are equally likely to feel all emotions, although gender rules shape differences in emotional expression. American women on average are more expressive than men, except when it comes to expressing anger at strangers. Both sexes are less expressive to a person of higher status than they, both sexes will do the emotion work their job requires, and some situations foster expressiveness in everybody.

Hans Selye argued that environmental stressors produce a general adaptation syndrome, in which the body responds in three stages: alarm, resistance, and exhaustion. If a stressor persists, it may overwhelm the body's ability to cope, and illness may result. Modern research has added to Selye's work. When a person is under stress or in danger, the hypothalamus sends messages to the endocrine glands along two major pathways. One activates the sympathetic division of the autonomic nervous system, releasing adrenal hormones from the inner part of the adrenal glands. In the other, the hypothalamus initiates activity along the HPA axis. When the stressors of poverty and unemployment become chronic, they can increase people's stress levels and increase their chances of illness. But responses to stress differ across individuals, depending on the type of stressor and the individual's own genetic predispositions. Researchers in psychoneuroimmunology (PNI) are studying the interaction among psychological factors, the nervous and endocrine systems, and the immune system (particularly the white blood cells that destroy harmful foreign bodies, called antigens).

Realistic optimism, conscientiousness, and having an internal locus of control improve immune function and also increase a person's ability to tolerate pain, live with ongoing problems, and recover from illness, possibly because they motivate people to take better care of themselves.

Researchers have sought links between emotions, stress, and illness. There is no “cancer-prone personality,” but chronic anger, especially in the form of cynical or antagonistic hostility, is a strong risk factor in heart disease. Major depression also increases the risk of later heart disease.

People who consciously suppress their emotions (caused by serious matters) are at greater risk of illness than people who acknowledge and cope with negative emotions. The effort to suppress worries, secrets, and memories of upsetting experiences can become stressful to the body.

Two ways of letting go of negative emotions include confession and forgiveness. The goal is to achieve insight and understanding, distance oneself from the bad experience, and let go of grudges. Forgiveness can be harmful, of course, if it keeps people in violent and abusive relationships.

An effective approach to coping is to focus on solving the problem (problem-focused coping) rather than on venting the emotions caused by the problem (emotion-focused coping).

Rethinking about a problem, which involves reappraisal, learning from the experience, and comparing oneself to others can provide new insights and a revised frame of mind.

Social support is essential in maintaining physical health and emotional well-being; it even prolongs life and speeds recovery from illness. A touch or a hug from a supportive partner calms the alarm circuits of the brain and raises levels of oxytocin, which may result in reduced heart rate and blood pressure. However, friends and family can also be sources of stress. In close relationships, couples who fight in a hostile and negative way show impaired immune function.