What is Stress?

Stress is often used to describe a certain physical and emotional state, but the definition of "stress" is rather subjective, as you will see below.

Hans Selye, an endocrinologist, is considered to first to use the term stress in a biological context in the 1930s. He defined it as the body’s non-specific response to any demand made on it.

Stress in not by definition synonymous with nervous tension or anxiety even though most of the population makes that connotation. The important thing to remember about stress is that certain forms are normal and essential. Selye termed negative stress “distress” and positive stress “eustress”. The system whereby the body copes with stress, the hypothalamic-pituitary-adrenal axis (HPA axis) system, was also first described by Selye. He pointed to an "alarm state", a "resistance state", and an "exhaustion state", largely referring to glandular status.

There are essentially 6 types of stressors…

  1. Physical: trauma (accidental or surgical), lack of sleep, intense exertion (physical activity or manual labour)

  2. Biochemical: drugs, alcohol, caffeine, nicotine, cleaning agents, pesticides, certain foods (that you have a sensitivity or intolerance to), vitamin and mineral deficiencies

  3. Mental: perfectionism, worry, anxiety, long work hours

  4. Emotional: anger, guilt, loneliness, sadness, fear

  5. Environmental: changes in temperature, wind, humidity

  6. Psycho-Spiritual: relationships, financial or career pressures, challenges with life goals, spiritual alignment and general state of happiness

Whatever the stressor is, it requires the body to make physical and chemical adjustments in order to maintain the necessary physiological balance for survival. After the threat has passed or a change has taken place, the “alarm” signs disappear. The body is still aroused but is adapting to the change. However, if the stressors continue to be present, the ability to adapt runs out and exhaustion occurs, causing damage to the person’s physical and emotional well-being.

Our lives are filled with many demands that continue over a long period of time. Demands such as work overload may result in distress. Unrelieved stress can take an emotional as well as physical toll, in the form of anxiety or depression, high blood pressure, cardiovascular disease, heart disease ulcers, allergies, asthma, or migraine headaches. If unattended, stress can seriously damage physical health, psychological well-being, and relationships with friends, family, and coworkers.

Selye conceptualized the physiology of stress as having two components: a set of responses, which he called the "general adaptation syndrome” (GAS), and the development of a pathological state from ongoing, unrelieved stress.

General Adaptation Syndrome

A diagram of the General Adaptation Syndrome model

A diagram of the General Adaptation Syndrome model

Physiologists define stress as how the body reacts to a stressor (a stimulus that causes stress), real or imagined. Acute stressors affect an organism in the short term; chronic stressors over the longer term.

Alarm is the first stage of stress. When the threat or stressor is identified or realized, the body's stress response initiates a state of alarm. During this stage, adrenaline will be released into circulation, thus bringing about the flight-or-fight response: the general discharge by the sympathetic nervous system of various hormones such as adrenaline or noradrenaline, which facilitates an immediate physiological reaction in preparation for rapid muscular action. These include the following:

  • Acceleration of heart and lung action

  • Paling/Flushing

  • Inhibition of stomach and upper-intestinal action to the point where digestion slows down or stops

  • Constriction of blood vessels in many parts of the body

  • Release of fat and glucose for muscular action

  • Dilation of blood vessels for the muscles

  • Inhibition of the lacrimal gland (tearing and salivation)

  • Dilation of the pupil

  • Relaxation of the bladder

  • Inhibition of erection

  • Loss of hearing

  • Tunnel vision, loss of peripheral vision

  • Shaking

The second stage is resistance. If the stressor persists, it becomes necessary to attempt some means of coping with the stress. Although the body begins to try to adapt to the strains or demands of the environment, the body cannot keep this up indefinitely, so its resources are gradually depleted.

Exhaustion is the third and final stage in the GAS model. At this point, all of the body's resources are eventually depleted and the body is unable to maintain normal function. The initial autonomic nervous system symptoms may reappear (sweating, raised heart rate, etc.). If stage three is extended, long-term damage may result, as the body's immune system becomes exhausted, and bodily functions become impaired, resulting in decompensation—the deterioration or failure of bodily systems and their functions.

Impact on Disease

Chronic stress can significantly affect the body's immune system, as can an individual's perceptions of, and reactions to, stress. The term psychoneuroimmunology describes the interactions between the mental state, nervous and immune systems, and research on the interconnections of these systems. Immune system changes can create more vulnerability to infection, and have an effect on auto-immune diseases. For example, stress-related changes in immune function have been observed to increase the potential of an outbreak of psoriasis for people with that skin disorder.

Chronic stress has also been shown to impair growth and development in children by lowering the pituitary gland's production of growth hormone, as in children associated with a home environment involving serious marital discord, alcoholism, or child abuse.

Chronic stress is seen to affect parts of the brain where memories are processed and stored. When people feel stressed, stress hormones are over-secreted, thus directly affecting the brain. This secretion is made up of glucocorticoids, including cortisol, which are steroid hormones that the adrenal gland releases.

Studies of female monkeys discovered that individuals suffering from higher stress had higher levels of visceral fat in their bodies. This suggests a possible cause-and-effect link, whereby stress promotes the accumulation of visceral fat, which in turn causes hormonal and metabolic changes that contribute to heart disease and other health problems.

However, in humans it has been shown that the stress response slows down or even stops various processes such as sexual responses and digestive function in order to focus on the stressful situation, typically causing negative effects like constipation, anorexia, erectile dysfunction, difficulty urinating, and difficulty maintaining sexual arousal. These are functions that are controlled by the parasympathetic nervous system and are suppressed by sympathetic arousal.

Prolonged stress responses may result in chronic suppression of the immune system, leaving the body open to infection. However, there is a short boost of the immune system shortly after the fight-or-flight response has been activated. This may be due to an ancient need to fight the infections in a wound that one may have received during interaction with a predator. 

Stress responses are sometimes a result of mental disorders such as post-traumatic stress disorder, in which the individual shows a stress response when remembering a past trauma, and panic disorder, in which the stress response is activated by the catastrophic misinterpretations of bodily sensations.

To learn more about stress, visit:

The American Institute of Stress

Stress–MEDLINE Plus