Stress can be defined in many different ways, depending on the person experiencing it and the perspective used to understand it. One basic definition of stress is "a psychological feeling of strain and pressure." Behavioral medicine and health psychology are two approaches to analyzing and discussing stress.

To scientists, a stressor is any action or situation that places special physical or psychological demands upon a person, and can be anything that can unbalance the individual's equilibrium. Stress may stem from a major life change, or it may be a built-in part of one's daily life; it can be a constant and unconscious background experience, like the noise of a city, or the daily chore of driving a car. When people are faced with demands to which they feel unable to adequately respond, they are motivated to do something to change the situation. The nature of this response depends on a combination of different factors, including the extent of the demand, the personal characteristics and coping resources of the person, the constraints on the person trying to cope, and the support received from others.

Distress vs. Eustress

Stress can be either positive (eustress) or negative (distress). Importantly, the body itself cannot physically discern between distress or eustress; the distinction is dependent on the experience of the individual experiencing the stress. Distress, or negative stress, has negative implications, and is usually perceived to be potentially overwhelming and out of a person's control. Catastrophes, illnesses, and accidents tend to be the focus of negative stress. Eustress, or positive stress, on the other hand, is the positive emotional or cognitive response to stress that is healthy; it gives a feeling of fulfillment or happiness. Eustress has a positive correlation with life satisfaction and hope because it fosters challenge and motivation toward a goal. Any event can cause either distress or eustress, depending on how the individual interprets the information. For example, traumatic social events may cause great distress, but also eustress in the form of resilience, coping, and fostering a sense of community.

Stress and Health

Prolonged psychological stress may negatively impact health, and has been cited as a factor in cognitive impairment with aging, depressive illness, and expression of disease. There is evidence that certain negative mental states (such as depression and anxiety) can directly affect physical immunity through the production of stress hormones, such as catecholamines and glucocorticoids. Stress management is the application of methods to either reduce stress or increase tolerance to stress. Relaxation techniques are physical methods used to relieve stress. Psychological methods include cognitive therapy, meditation, and positive thinking, which work by reducing the response to stress. Improving relevant skills, such as problem-solving and time-management skills, reduces uncertainty and builds confidence, which also reduces the reaction to negative stress-causing situations in which those skills are applicable.

Athletic competition

Competing in athletic events often leads to eustress.