2 Stress and Health

Stress and its sources

Stress is the coordinated response to a challenge that threatens—or is perceived to threaten—a person’s well-being or ability to cope. It includes the person’s appraisal of the challenge and the resulting bodily, emotional, and behavioral responses. The challenge itself is a stressor.

Stressors may be physical, such as injury, illness, pain, or extreme temperatures, or psychological and social, such as conflict, caregiving demands, financial hardship, discrimination, work pressure, or uncertainty. Major life changes can be stressful even when welcome, and smaller everyday hassles may accumulate. Stress may arise from a single event, repeated events, or an ongoing condition; the source alone does not determine how stressful it feels.

Appraisal and individual differences

Stress depends in part on appraisal: how a person interprets a situation and their ability to manage it. In a common model, a person first evaluates whether an event matters and whether it represents harm, threat, or challenge. They also assess the options and resources available to them, such as time, skills, health, and support.

An upcoming exam, for example, may seem manageable to someone who feels prepared but overwhelming to someone who feels unprepared and unsupported. Appraisal may be rapid and partly automatic, not a deliberate calculation.

People differ in their appraisals, physiological reactivity, and recovery. Prior experience, health, personality, learned coping patterns, and social resources can all matter. The same person may react differently to the same stressor at different times. Stress therefore reflects the interaction between perceived demands and the resources a person believes they can use, rather than being simply a property of an event.

The body’s stress responses

The body responds to stress through interacting nervous and hormonal systems. The fast-acting sympathetic–adrenal–medullary (SAM) system involves sympathetic nerves and the adrenal medulla releasing norepinephrine and epinephrine. Heart rate and blood pressure rise, energy becomes more available, and blood flow shifts to support action. These changes prepare the body to respond to a challenge. As the challenge passes, parasympathetic activity helps the body return toward its resting state.

A slower response involves the hypothalamic–pituitary–adrenal (HPA) axis. The hypothalamus signals the pituitary gland, which signals the adrenal glands to release cortisol. Cortisol helps regulate energy use and other functions during a challenge.

The effects of cortisol are not inherently harmful: they are part of an adaptive response. Their consequences depend on the timing, intensity, and duration of the response.

Stress, health, and recovery

Short-lived stress responses can be useful by mobilizing attention and energy for immediate demands. When activation is frequent or recovery is inadequate, however, the body may bear a cumulative physiological burden called allostatic load.

Over time, persistent stress can affect cardiovascular, metabolic, immune, sleep, and emotional functioning, and may contribute to health risks. These relationships are complex: stress does not inevitably cause illness. Effects vary with the stressor, its duration, a person’s health and vulnerability, and available coping resources.

Stress can also influence health through behavior. Under pressure, people may sleep less, become less active, change eating habits, or use substances; others may seek care or practical support. These behaviors can in turn affect health, so stress may influence both bodily processes and everyday choices.