The fight or flight response is commonly defined as a physiological reaction to a perceived attack or threat. This bodily response was first discovered by Walter Cannon (1929) while observing animals’ behavior under stressful circumstances; his findings revealed that when animals feel threatened, the sympathetic nervous system reacts by providing the organism with the resources it needs to avoid the threatening situation, either by fighting back or running away. This process causes the body to undergo a number of physiological changes, including increased heart rate and breathing rate (to provide the brain and the muscles with more oxygen), improved coagulation in case of physical injuries, auditory exclusion, contracted muscles, dilated pupils / improved sight, increased sweating to keep the body cool and goosebumps (a reaction that is found exclusively in humans), which have been found to make people look bigger and, therefore, more frightening.

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Later research revealed that the fight or flight response is an alarm reaction that can be triggered by a variety of factors, including anger, aggression and even internal stressors. For example, those who suffer from anxiety-related disorders tend to perceive apparently harmless situations such as meeting new people or even going to the supermarket as possible dangers from which they need to protect themselves; as a result of their excessive anxiety, their sympathetic nervous system is particularly sensitive and causes them to experience increased physiological arousal regardless of whether their survival is actually being threatened.

Under life threatening circumstances, the human body has been found to release a number of hormones, especially cortisol, epinephrine (more commonly known as adrenaline) and noradrenaline, which facilitate reliance on intuitive behaviors as well as faster physical reactions to perceived threats, thus enabling people to either escape or defend themselves in a much more effective manner. As Harari & Legge (2001, p. 75) pointed out, the fight or flight response is an evolutionary mechanism that has been passed down from generation to generation, thus allowing both humans and animals to deal with threatening challenges for thousands of years. It follows that those who are born with a stronger fight or flight response are more likely to survive when challenged and, therefore, more likely to reproduce. However, when one experiences the aforementioned physiological changes without being able to increase their physical activity (for example, when driving in traffic), the fight or flight response is likely to have a negative impact on their body, leaving them feeling extremely nervous and edgy.

In the 1930s, Selye expanded Cannon’s theory to encompass the harmful effects of over-arousal; his studies revealed that the fight or flight response is activated as soon as the hormones released by the endocrine system reach the bloodstream and that neither animals nor humans can maintain an alarm response for more than a few hours without dying. In order to survive, the organism enters the so-called “resistance stage”, when the physiological changes experienced during the previous stage are reversed to enable the body to recover and prepare for a new threat. Similarly to the first “alarm reaction” stage, one can only resist for so long as after some time, their organism would be too exhausted to react in anyway. This is when the “stage of exhaustion” begins, making it impossible for the body to recover from the previous stages. It is important to keep in mind that while Cannon and Selye focused primarily on external stressors, research has clearly demonstrated that social and psychological factors can also activate a fight or flight response, thus prompting individuals to experience increased physiological arousal in the absence of actual external stressors (Harari & Legge, 2001, pp. 75-76).

  • Harari, P. & Legge, K. (2001). Psychology and Health. Oxford, UK: Heinemann.
  • Walter Bradford Cannon (1929). Bodily changes in pain, hunger, fear, and rage. New York: