The Three Stages of Stress: General Adaptation Syndrome

Medically reviewed by April Justice, LICSW
Updated December 1, 2023by BetterHelp Editorial Team

Nearly 90 years ago, Hungarian/Canadian physician Hans Selye described a physiological mechanism through which organisms adapt to their environment. Unbeknownst to him, his work would go on to form the basis of nearly a century of research into how humans manage stress physically and mentally. Selye's theory, which he termed general adaptation syndrome, is still relevant today. Modern research has expanded on his work to further explain how stress works in the mind and body.

Is Your Stress Burden Overwhelming?

The Start Of Stress: Selye's General Adaptation Syndrome

When Selye first published his work in Nature in 1936, the term "stress" had not yet been used in the way many people are familiar with today. Selye referred to stressors as "noxious agents" and, being a medical doctor, was chiefly concerned with the stress-inducing effects of injury and illness on bodily systems. His work derived from many experiments he performed on laboratory rats, which he used to conclude how stress might affect the human body.

Selye's work led to the development of his general adaptation syndrome (GAS) theory. The GAS describes a three-stage response to stress, which is outlined below.

Stage 1: Alarm/Reaction Phase

In the first stage of the GAS, a stressor disturbs the stability of the body's normal functions, also known as homeostasis. The rate of the autonomic nervous system increases rapidly. The autonomic nervous system controls involuntary physiologic processes like heart rate, blood pressure, and respiration. The rapid increase in the rate of autonomic functions gives the organism physical strength to guard itself against an external threat or internal disturbance. Typically, the alarm phase is short-lived and sometimes may only last for a few seconds.

Although it was first described years after Seyle's development of the GAS, the alarm phase is often considered synonymous with the modern concept of fight-or-flight. Fight-or-flight is a frequently discussed topic in contemporary stress research. It is a survival mechanism that allows organisms to react to life-threatening situations quickly by increasing the rate of autonomic functions, as in the alarm stage of the GAS.

Stage 2: The Resistance/Adaptation Stage

The second stage of the GAS typically represents the body's efforts to return to a state of normal homeostasis. Stage two generally consists of a lowering heart rate, reduced blood pressure, and slower respiration if the stressor is no longer present. However, if the stressor is still present, the organism must expend considerable energy to "resist" the threat of the stressor.

The effect is likely most obvious when considering fight-or-flight in the context of nature. For example, an animal running from a predator will eventually run out of energy, and their body will no longer be able to resist the stressor (the hungry predator) by fleeing. If the animal has successfully escaped, their resistance has "adapted" them to the stressor by moving them far away from the source of the threat.

If the animal cannot adapt to (in this case, escape) the stressor, its body will continue to produce stress hormones that elevate heart rate, blood pressure, and respiration. Despite the continued activation of these bodily processes, the animal has only a finite amount of energy and will eventually succumb to fatigue. In this example, the threat is pronounced and relatively short-lived; most animals cannot run at full speed for more than a few minutes at a time.

However, in other situations, especially those likely to be encountered by humans, the resistance/adaptation stage may last much longer, sometimes for days, weeks, months, or years. Problems occur at this stage if the biological, psychological, and social responses to the threat are insufficient to manage the threat effectively. As the resistance/adaptation stage grows longer, it is more likely that a person will experience fatigue, cognitive lapses, irritability, and lethargy.

Stage 3: Exhaustion Phase

An organism that can successfully adapt to a stressor will not reach the exhaustion phase. The third phase of the GAS occurs when an organism cannot rest or recharge when adapting to a stressor. In some cases, the organism has no tools at its disposal through which to adapt to the stressful environment, and adaptation never occurs.

In the predator/prey example in the description of stage two, the exhaustion phase will likely be short-lived as the predator catches up to the animal they are chasing. For humans, common stressors rarely include being chased by hungry animals, and the exhaustion phase may be much longer, potentially lasting indefinitely. Psychologists and therapists use the term chronic stress to refer to long-term, ongoing activation of the stress-response system in humans.

How Chronic Stress Works

Today, researchers have a much clearer picture of how the stress-response system works in humans. Contemporary research has identified two distinct stress-response systems in humans: the fast and slow response systems. The fast response system allows humans to respond to threats rapidly, often before the threat is fully perceived. In terms of chronic stress, the slow response system is likely more impactful and will be the focus of this section.

The hypothalamic-pituitary-adrenal (HPA) axis describes the biological system that controls the slow response system in humans. It consists of three components:

  • The hypothalamus acts as a link between the brain and the autonomic nervous system.
  • The pituitary gland releases communication hormones when commanded by the hypothalamus.
  • The adrenal gland releases hormones that activate the fight-or-flight response.

Although it is described as the slow response system, activation of the HPA axis occurs rapidly. When a threat is perceived, the hypothalamus signals the pituitary to release adrenocorticotropic hormone (ACTH). ACTH travels through the circulatory system until it reaches the adrenal gland, specifically the adrenal cortex. When triggered by ACTH, the adrenal cortex releases cortisol, a well-known stress hormone.

The body's fast response system focuses on immediately increasing blood pressure, heart rate, and respiration. It is designed to provide an organism with a sudden burst of energy to escape a potential threat. On the other hand, the slow response system initiates changes in the body that allow for a sustained release of energy.

Getty/The Good Brigade

Why Chronic Stress Can Be Dangerous

A normal stress response can include stages one and two of the GAS; a threat is perceived, and the stress response activates until the danger is no longer detected. At that point, bodily systems return to baseline levels. On the other hand, stage three of the GAS indicates a maladaptive stress response; the threat is constantly detected, and the HPA axis remains activated indefinitely.

Ongoing activation of the HPA axis strains nearly every organ system of the body. Below is a short list of possible physical complications that researchers have identified:

  • Cardiovascular disease, including coronary artery disease, stroke, and high blood pressure
  • Weakened immune system.
  • Weakening of the gastrointestinal tract.
  • Reduced sleep quality and increased fatigue.
  • Addison's disease, Cushing syndrome, and other diseases of the adrenal system.

In addition, chronic stress is associated with an increased risk of developing the following mental health concerns:

  • Depression and suicidal thoughts*
  • Anxiety
  • Self-harm behaviors
  • Low self-esteem
  • Cognitive deficits such as lowered concentration and reduced executive function

*If you or a loved one is experiencing suicidal thoughts, reach out for help immediately. The 988 Suicide and Crisis Lifeline can be reached at 988 and is available 24/7.

Managing Chronic Stress

It may seem like chronic stress is inescapable in modern society. Although everyone will likely experience stress at some point in their lives, there are basic steps you can take to prevent the worst effects of chronic stress.

  • Set appropriate boundaries. One of the most effective ways to reduce chronic stress is to ensure that commitments are manageable. Take time to ensure you prioritize tasks and cut back on anything that is not absolutely essential. Limit how much is on your plate until your stress level decreases. 
  • Activate your support system. Friends and family can be significant sources of stress relief. They may have ideas about how to manage your stress practically, and being able to voice your challenges to others may be beneficial. 
  • Make at least one health commitment. Because chronic stress can significantly impair physical health, consciously focusing on becoming healthier may be beneficial. Start by choosing one health-positive action to commit to, such as cutting back on caffeine, quitting smoking, adopting an exercise regimen, or improving sleep quality. 

Can Therapy Help With Chronic Stress?

If your stress is overwhelming, consider speaking with a therapist to help you identify strategies for reducing stress and addressing underlying causes. A therapist can help you manage chronic stress using evidence-based techniques that are likely to be effective, such as mindfulness and biofeedback. A therapist may also be able to help you find practical solutions to problems in your life that may be increasing your stress.

If your life is already particularly stressful, online therapy may be a good option. Visiting a therapist online potentially removes many barriers to therapy, such as traveling to an office. You can also choose from therapists outside of your local area. 

Although online therapists administer psychotherapy remotely, evidence indicates it effectively treats mental health conditions like stress, depression, and anxiety.

Getty/Vadym Pastukh
Is Your Stress Burden Overwhelming?


The modern concept of stress was first revealed nearly a century ago when Hans Seyle introduced his general adaptation syndrome theory. He proposed three stages of stress response. Stages one and two represent the early version of what is known as the fight-or-flight response today. Stage three is characterized by the breakdown of stress-response systems that have been activated for too long, aligning closely with today's concept of chronic stress. Chronic stress can be reduced by managing commitments, increasing physical health, and adopting coping strategies for relaxation. If chronic stress is persistent and severe, therapy provides a viable option for relief.

Ease stress and mental exhaustion

The information on this page is not intended to be a substitution for diagnosis, treatment, or informed professional advice. You should not take any action or avoid taking any action without consulting with a qualified mental health professional. For more information, please read our terms of use.
Get the support you need from one of our therapistsGet Started