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What is Stress and How Does it Impact Your Health?

In the past decades ‘stress’ has become a buzzword. We hear it everywhere, everyone is stressed, everything becomes a stressor, and society leads us to stressful lives.

But is that really true? Is stress such a bad thing? What is stress after all? And what are its impacts on your health? 

What is ‘stress’?

The term ‘stress’ has been used for centuries in physics (used since 17th century in Hooke’s Law of Elasticity),1 however it had none of its contemporary connotations before the 1920s. In 1926 Walter Cannon used ‘stress’ to refer to external factors that disrupted what he called homeostasis,2 and in 1935 he published “Stresses and strains of homeostasis”.3 Homeostasis is a complex dynamic equilibrium, also considered any self-regulating process by which an organism tends to maintain stability while adjusting to conditions that are best for its survival.4 But the term ‘stress’ as it is currently used was coined by Hans Selye in 1936. Selye defined ‘stress’ as “the non-specific response of the body to any demand for change.”5

In his laboratory experiments, Selye noted that animals subjected to acute but different harmful physical and emotional stimuli all exhibited the same pathologic changes, such as stomach ulcerations, shrinkage of lymphoid tissue and enlargement of the adrenals. Later, Selye was able to demonstrate that animals, when subjected to persistent noxious stimuli could develop various diseases similar to those seen in humans, such as heart attacks, stroke, kidney disease and rheumatoid arthritis.6

Selye’s theories attracted much attention, and the term ‘stress’ became a buzzword and was used in various contexts, ignoring Selye’s initial definition. Some people started using ‘stress’ to refer to their unpleasant work environment, others to the chest pain that the work situation created and others even to the result of these repeated exposures, such as an ulcer or heart attack.6

This led to a lot of confusion in the scientific world and one physician, in a 1951 issue of the British Medical Journal, using verbatim citations from Selye’s own articles concluded that “Stress, in addition to being itself, was also the cause of itself, and the result of itself.7

Finding an acceptable definition of stress was a struggle for Selye his entire life and, in his 1973 article he lamented “Everybody knows what stress is, and nobody knows what it is”.8 The main issue, as Selye pointed out, is that the concept of stress is often confused with the concept of stressful stimuli, stressors, stress responses, and stress effects.9

how stress impacts your health

How to understand stress?

A possible framework to understand stress may contemplate 5 elements:10

  • Stressful stimuli: agents that can induce the formation of stressors or transfer to stressors.
  • Stressors: factors with the potential to directly challenge homeostasis.
  • Stress: a state of homeostasis being challenged.
  • Stress response: a compensatory process aimed to restore homeostasis.
  • Stress effects: are biological consequences resulting from the struggle with stressors, which may include re-establishing homeostasis that promotes health (positive effects) or causing damage to the body or even diseases (negative effects).


Let’s use the example of oxidative stress. Oxidative stress is an imbalance between free radicals and antioxidants in the body that can cause damage and play an important role in the development of disease, mainly chronic diseases such as cancer.

Oxidative stress:

  • Stressful stimuli: the factors that stimulate the generation of reactive oxygen species (ROS, also called oxygen free radicals) (for example, pesticides in food, pollution, radiation, etc)
  • Stressor: reactive oxygen species (ROS)
  • Stress (oxidative stress): disruption of redox signaling and control caused by ROS (not enough antioxidants to balance free radicals)
  • Stress response: the response that the body attempts to restore redox homeostasis (in this case, oxidative stress response)
  • Stress effects: the resulting biological consequences (e.g., when the stress is repeated over time, chronic disease, such as diabetes, neurodegenerative diseases or cancer)


What is stress then?

Stress can be considered a state. A state of homeostasis (dynamic equilibrium) being challenged.10


What are the origins of the stress response?

The stress response is based on a perceived or real threat, which in humans and other animals’ triggers certain coping responses, ‘fight-or-flight’ being one of the most common in mammals. When ‘fight-or-flight’ is feasible, there is an increase in autonomic and hormonal activities that maximize the possibilities for muscular exertion.11 Fight-or-flight response can be considered a relic of our evolutionary heritage to deal with danger and it served us well in the past, by allowing us to survive attacks by predators and other natural threats.

In contrast, there are certain adverse situations for which there might be no active coping response. In this situation mammals may engage in a vigilance response that involves sympathetic nervous system (SNS) arousal accompanied by an active inhibition of movement and shunting of blood away from the periphery. This response is often called “freeze”.11


Why do these responses happen?

In 1994 Dr. Stephen Porges developed the Polyvagal Theory as a possible explanation to better understand these human responses. The Polyvagal Theory describes how the nervous system relates to the environment, and its different responses to safe versus threatening environments. This theory explains three different circuits by which the vagus nerve communicates between distinct parts of the brain and the heart, which are influenced by environmental factors and elicit different physiological and behavioral responses.12

According to the polyvagal theory, there are 3 states in the Autonomic Nervous System (ANS):

  • “Rest and Digest” – Activates Parasympathetic Nervous System – Safe environments promote increased vagal influence and spontaneous social engagement behaviors. It is considered a state of relaxation.
  • “Fight or Flight”– Activates Sympathetic Nervous System – Vagal withdrawal is linked to mobilization of the fight or flight response. It is considered a stress
  • “Freeze” – Activates Parasympathetic and Sympathetic Simultaneously – Shutdown mode when faced with danger. Considered a state of dissociation.


Is Stress Good or Bad?

Over the past decades, the concepts of stress have evolved, and the implications of stress have expanded greatly. Stress is not considered solely the hypothalamic-pituitary-adrenal (HPA) axis and the series of compensatory sympathoadrenal responses when homeostasis is threatened. Stress now includes not only the negative aspects of related threats to health and life, but also the positive aspects such as adapting to the existing environment and anticipating future challenges.10

Researchers now consider that an optimal stress level is crucial for health, while an excessive or inadequate stress level might impair development, growth, and body composition, and lead to pathological conditions.10

Therefore, a better categorization of stress may differentiate between ‘eustress’ and ‘distress’,10 concepts that had already been introduced by Selye in 1975.9

  • Eustress’: good stress. Homeostasis mildly challenged by moderate levels of stressors. Might induce a mild stress response, enhance the buffering capacity of homeostasis and benefit health.
  • ‘Distress’: bad stress. Homeostasis strongly challenged by high levels of stressors. Might induce a severe stress response, impair homeostasis, and endanger health.

Some authors also propose the concept of ‘sustress’. From the Latin ‘sus‘, which means ‘less than normal’, and ‘stress’, meaning ‘no or inadequate stress’. Sustress might reduce the buffering capacity of homeostasis and threaten health.10

From this perspective, stress may induce both beneficial and harmful effects. It may be beneficial when it involves preserving homeostasis of the cells or even species, leading to continued survival. However, stress can also be harmful and unfortunately the negative effects of stress tend to receive more attention due to its impact on health and role on disease development.13


When and why does stress become harmful to health and may lead to disease?

As Selye stated, “It’s not stress that kills us, it is our reaction to it.14

Although stress responses evolved as adaptive processes, severe, prolonged stress responses might lead to tissue damage and disease. For example, repetitive perception of stress leads to continuous activation of the sympathetic nervous system (SNS). The activation of the SNS then leads to the chronic stimulation of the cardiovascular system, with constant increases in blood pressure and vascular hypertrophy. If this stimulation is repeated and continued, with time, the high and rapidly shifting blood pressure may lead to chronic inflammation, formation of plaque and damaging of the arteries. A roadmap to cardiovascular disease.

  • Why does this happen?

Evolution has provided mammals, and us humans, with reasonably effective homeostatic mechanisms to deal with short-term stressors. When perceiving an acute stressful event, there is a cascade of changes in the nervous, cardiovascular, endocrine, and immune systems. These changes constitute the stress response and, short term, tend to be typically adaptive.11,14 This is especially true for young and healthy people, for whom the acute stress can be beneficial. Even chronic stress, when imposed on individuals who have good coping mechanisms and are generally optimistic may be beneficial.

This is often not the case in older or unhealthy individuals, especially when the perceived threat is persistent, as the stress response can become maladaptive if it is repeatedly or continuously activated, usually called chronic stress. In this case, the long-term effects of the continuous response to stress may start to cause health problems.11,14


What are the negative effects of stress?

First, why does stress seem to be a bigger issue for humans than other mammals?

It is indeed interesting to observe that the adverse effects of chronic stressors are particularly common in humans. As some authors explained, this might be partially because of human’s higher capacity for symbolic thought and association. Human thought processes may elicit persistent stress responses to a broad range of adverse living and working conditions, which for other mammals would not pose a threat.11

What are the signs and symptoms of stress?

The American Institute of Stress lists 50 common signs and symptoms of stress15 and alerts for the wide range of nefarious effects that stress can have on mental and physical health. Some of these include physical symptoms, such as frequent headaches, jaw clenching or pain, neck ache, back pain, muscle spasms, but there are also many mental and emotional signs, such as forgetfulness, disorganization, confusion and feelings of loneliness or worthlessness.

Chronic stress affects emotions, mood and behavior along with various systems, organs and tissues all over the body. These effects can be felt on various bodily systems and affect your overall health and wellbeing. Some of the most affected systems include nervous, immune, musculoskeletal, gastrointestinal, respiratory, cardiovascular, endocrine and reproductive.15

What diseases may result from stress?

Studies have demonstrated an association between psychosocial stressors and disease, namely:11,15

  • Chronically elevated levels of inflammation
  • Coronary heart disease
  • Hypertension
  • Upper respiratory disease
  • Human Immunodeficiency Virus
  • Autoimmune disease
  • Mental health disturbances, such as mood disorders, irritability, anxiety, depression
  • Headaches and migraines
  • Insomnia and sleep disorders


Why are some people more affected by stress than others?

There is a complex relationship between psychological, behavioral, and biological factors, stressors and stress responses and the development of chronic disease.11 As we mentioned earlier, young versus old, healthy versus unhealthy, with or without coping strategies, are all factors that influence the effects of stress on the individual.

Knowing that the effect of stress will always be dependent on this individuality, researchers have listed some of the factors that are associated with the relationship between stress and disease, such as:11

  • Nature, number, and persistence of the stressors
  • Individual’s biological vulnerability (i.e., genetics, constitutional factors)
  • Psychosocial resources and coping mechanisms



Final words on stress

Stress, which functions through a complex stress system, can be considered a state of homeostasis being challenged. Based on the type of stress, it can be beneficial or harmful. There are three basic types of stress: distress, eustress, and sustress.10

  • Distress may impair normal functioning of the body and overtime lead to disease. If stressors are too strong and too persistent in individuals who are biologically vulnerable because of age, genetic, or constitutional factors, stressors may lead to disease, particularly when individuals possess few coping skills and psychosocial support.
  • Eustress, on the other hand, plays an essential role in the process of adaptation, especially in the ability to assess and adequately manage stressors. Eustress, therefore, also prepares the individual by giving him tools to deal and survive future challenges. This is especially true in young and healthy individuals, with good coping mechanisms and psychosocial resources.
  • Finally, sustress, whether in the form of no stress or inadequate stress, may weaken the basal activity of the stress system and therefore, impair the response capacity of the system to present and future challenges.


After all, it seems that an optimal level of stress is essential for building biological defenses, through a continuous search for balance and equilibrium within challenging situations, leading to stimulation and benefits to adaptation that can guarantee normal life processes.10

Go find yourself some good stress!


  1. Robert Hooke, De Potentia Restitutiva, or of Spring. Explaining the Power of Springing Bodies, London, 1678.
  2. W. B. Cannon; Physiological Regulation of Normal States: Some Tentative Postulates Concerning Biological Homeostatics; IN: A. Pettit (ed.); A Charles Richet: ses amis, ses collègues, ses élèves; p. 91; Paris; Éditions Médicales; 1926.
  3. Cannon WB. Stresses and strains of homeostasis. Am J Med Sci. 1935;189(1):13–14. doi: 10.1097/00000441-193501000-00001.
  4. Definition of Homeostasis., accessed July 21, 2021
  5. Selye H. A syndrome produced by diverse nocuous agents. Nature. 1936;138(3479):32–32. doi: 10.1038/138032a0.
  6. The American Institute of Stress – What is Stress?, accessed July 20, 2021.
  7. Humphrey, J. H. (2005). Anthology of stress revisited: Selected works of James H. Foreword by Paul J. Rosch. New York, NY: Nova Science Publishers.
  8. Selye H. The evolution of the stress concept. Am Sci. 1973 Nov-Dec;61(6):692-9. PMID: 4746051.
  9. Selye H. Confusion and controversy in the stress field. J Human Stress. 1975 Jun; 1(2):37-44.
  10. Lu S, Wei F, Li G. The evolution of the concept of stress and the framework of the stress system. Cell Stress. 2021 Apr 26;5(6):76-85. doi: 10.15698/cst2021.06.250. PMID: 34124582; PMCID: PMC8166217.
  11. Schneiderman N, Ironson G, Siegel SD. Stress and health: psychological, behavioral, and biological determinants. Annu Rev Clin Psychol. 2005;1:607-28. doi: 10.1146/annurev.clinpsy.1.102803.144141. PMID: 17716101; PMCID: PMC2568977.
  12. Porges SW. Orienting in a defensive world: mammalian modifications of our evolutionary heritage. A Polyvagal Theory. Psychophysiology. 1995 Jul;32(4):301-18. doi: 10.1111/j.1469-8986.1995.tb01213.x. PMID: 7652107.
  13. Yaribeygi H, Panahi Y, Sahraei H, Johnston TP, Sahebkar A. The impact of stress on body function: A review. EXCLI J. 2017 Jul 21;16:1057-1072. doi: 10.17179/excli2017-480. PMID: 28900385; PMCID: PMC5579396.
  14. Selye H. McGraw-Hill; New York: 1956. The stress of life.
  15. The American Institute of Stress – What is Stress?, accessed July 22, 2021.