General Adaptation Syndrome

A profound physiological response of an organism to severe stress (acute or chronic) that occurs in three stages: an alarm or mobilization stage; a resistance stage; and a recovery or exhaustion stage.

The concept of general adaptation syndrome (GAS) was popularized by an Austrian-Canadian endocrinologist named Hans Selye (1907–1982), who began working on the issue of stress in 1936 after he moved to Canada. Although Selye's work led to the recognition of and research into the treatment of such stress-related psychiatric disorders as acute stress disorder and post-traumatic stress disorder (PTSD), the commercialization of stress-management techniques and the loose usage of the term “stress” in the 1980s and 1990s resulted in a loss of interest in GAS itself. There have been very few papers published on GAS in medical journals since the late 1990s. In addition, the 2011 revelation of Selye's funding by the tobacco industry in the 1960s and his agreement at that time to promote smoking as a legitimate form of stress relief has led to skepticism regarding the scientific integrity of certain aspects of stress research.


Selye's work in endocrinology in the early 1930s was the background of his discovery of stress as a significant factor in physical and emotional disorders. Selye had been performing experiments on the endocrine system of laboratory rats, injecting them with various irritants only to discover that it was apparently the stress of the hypodermic injections rather than the specific substances injected that caused the rats to develop stomach ulcers, swelling of the adrenal glands, and other physical symptoms. He then turned his attention to the fact that people with a range of disorders can develop similar symptoms as a result of what he initially called “nocuous agents” and later termed stress.

Selye himself acknowledged his dependence on two previous physiologists, the Frenchman Claude Bernard (1813–1878), who coined the phrase milieu intérieur to describe the body's internal environment; and the American Walter Cannon (1871–1945), who based his concept of homeostasis on Bernard's work; invented the expression “fight or flight response” ; and was the first to use the word “stress” to describe external factors that disrupt homeostasis.

Selye's innovation was to expand the concept of stress beyond the fields of biology and physiology and extend it into ordinary human experience. Prior to the 1930s, the word was simply not used as an explanation of human diseases and disorders. Selye's definition of stress was a very broad one: “the nonspecific response of the body to any demand placed upon it.” Selye was also the first to observe that a positive event like a job promotion, marriage, or becoming financially successful could place as many demands on the human organism as a negative event like unemployment, failure in school, or the loss of a loved one. He devised the term “eustress” to denote this type of positive stress.

Stages of general adaptation syndrome

Selye distinguished three stages in what he termed general adaptation syndrome or GAS. In his words, “I call this syndrome general because it is produced only by agents which have a general effect upon large portions of the body. I call it adaptive because it stimulates defense…. I call it a syndrome because its individual manifestations are coordinated and even partly dependent upon each other.” The first stage—alarm—Selye divided into two phases: shock, in which the body's immediate reaction to the stressor is a brief period of subnormal functioning; and antishock, in which the body responds by activating the hypothalamic-pituitary-adrenal (HPA) axis; producing the stress hormone cortisol; and increasing blood pressure, muscular tonus, and the levels of glucose in the blood.

Selye termed the second stage of the syndrome resistance. In this stage, the body attempts to adjust or adapt to the stressor if it persists over time; however, the body cannot maintain its resistance to the stressor indefinitely, and its resources are gradually depleted.

The third stage is either recovery or exhaustion. If the body successfully adapts to the stressor or the stressor is removed, homeostasis is restored and the body's cells begin to regenerate. On the other hand, if the body cannot adapt to or escape the stressor, the body's immune function is damaged, other functions are impaired, and the person develops such illnesses as peptic ulcers and other digestive complaints, cardiovascular disorders, and depression or an anxiety disorder.

Stress management and treatment

Given Selye's very general definition of stress, stress management techniques and the treatment of stress-related disorders have been highly individualized since the 1980s. It has long been recognized that people vary in their responses to stress on the basis of such factors as age, general level of health prior to the stressful event, genetics, personality traits (particularly neuroticism), and childhood experiences of trauma.

Another important factor is the individual's perception of the stressor: some people thrive on specific challenges (such as extreme sports) while others do not. People also vary considerably in their evaluations of such commonplace stressors as highway driving, school examinations, job interviews, public speaking, athletic competition, financial worries, and many others. More recently, it has been found that the simple belief that stress has an adverse effect on health can be a self-fulfilling prophecy: a study performed at the University of Wisconsin reported that it is the perception of stress as harmful to health rather than the stressor itself that increases a person's susceptibility to stress-related illness.


A steroid hormone released by the adrenal gland during stressful situations. It functions to raise blood sugar levels, suppress the immune response, and assist the metabolism of carbohydrates, fats, and proteins.
Endocrine glands—
Glands that secrete their products (hormones) directly into the bloodstream rather than indirectly through ducts.
A term coined by Selye to refer to positive stress, such as the stress resulting from the birth of a child, a job promotion, completing one's education, etc.
The process that maintains the internal stability of the human body's physiological processes in response to changes in the external environment. The word was first used by Walter Cannon in 1926.
Hypothalamic-pituitary-adrenal (HPA) axis—
A complex set of interactions and feedback mechanisms among the three major endocrine glands involved in the body's response to stress: the hypothalamus and pituitary glands in the brain and the adrenal glands in the kidneys.
Stress management—
A general term for a variety of techniques and psychotherapies intended to help people improve their ability to cope with chronic stress and raise their level of day-to-day functioning. Common stress management techniques include physical exercise, cognitive behavioral therapy, prayer and meditation, yoga, time management, deep breathing, and relaxation techniques.

See also Post-traumatric stress disorder (PTSD); Stress management.



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Keller, A., et al. “Does the Perception that Stress Affects Health Matter? The Association with Health and Mortality.” Health Psychology 31 (September 2012): 677–684. Available online at .

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Szabo, S., Y. Tache, and A. Somogyi. “The Legacy of Hans Selye and the Origins of Stress Research: A Retrospective 75 Years after His Landmark Brief ‘Letter’ to the Editor of Nature.” Stress 15 (September 2012): 472–478.

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American Institute of Stress, 6387B Camp Bowie Blvd., #334, Fort Worth, TX, 76116, (682) 239-6823, Fax: (817) 394-0593,, .

Canadian Institute of Stress, (416) 236-4218,, .

Genital stage see Psychosexual stages