The Three Stages Of Stress: General Adaptation Syndrome

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 at least a century of research into how humans respond to 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.

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. Hans 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 conclusions were 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. GAS describes a three-stage response to stress, including the alarm reaction and the resistance and exhaustion phases. Below, we’ve outlined the alarm, resistance, and exhaustion stages and what each one entails. 

Stage 1: The alarm/reaction phase 

In the first stage of general adaptation syndrome, a stressor (i.e., a real or perceived threat) triggers the central nervous system, disturbing the stability of the body's normal functions, also known as homeostasis. The rate of the autonomic nervous system—which controls involuntary physiologic processes like heart rate, blood pressure, and respiration—increases rapidly. This protective response gives the organism physical strength to guard itself against an external threat or internal disturbance. Typically, the physiological response to the alarm phase is short-lived and sometimes may only last for a few seconds. 

Alarm reaction stage and fight-or-flight

Although it was first described years after Selye's development of GAS, the alarm phase of the physical stress response is often considered synonymous with the modern concept of the fight-or-flight response. This response is widely discussed in contemporary stress research. It is a natural reaction that allows organisms to respond to life-threatening situations quickly by increasing the rate of autonomic functions, as in the alarm stage of the general adaptation syndrome.

Physical signs of alarm reaction/fight-or-flight

Initial symptoms of the alarm reaction stage (or fight-or-flight) may include physical signs. Some of these physical symptoms may include: 

• Increased heart rate
• Excessive sweating
• Muscle tension
• Nausea
• Rapid or shallow breathing

Stage 2: The resistance/adaptation stage 

The second stage of general adaptation syndrome is known as the resistance stage, and it typically represents the body's efforts to return to a state of normal homeostasis. Stage two generally enlists the parasympathetic nervous system and consists of a lowered heart rate, reduced blood pressure, and slower respiration, as long as the stressor is no longer present. However, if the stressor is still present, the organism must expend considerable energy as the body attempts to "resist" the threat of the stressor.

The effect is likely most obvious when considering the fight-or-flight response 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 body’s response (e.g., resistance) has "adapted" them to the stressor by moving them far away from the source of the threat.

If the animal cannot adapt to (or, in this case, escape) the stressor, the body remains alert and will continue to produce stress hormones that elevate heart rate, blood pressure, and respiration. Despite the continued activation of fight-or-flight, 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 after prolonged exposure if the biological, psychological, and social responses to the threat are insufficient to manage the threat effectively. As the resistance/adaptation stage grows longer and stress tolerance decreases, it becomes more likely that a person will experience fatigue, poor concentration, cognitive lapses, irritability, and lethargy.

Stage 3: The exhaustion phase 

An organism that can successfully adapt to a stressor will not reach the final stage of stress, known as the exhaustion stage. The third phase of stress occurs when an organism cannot rest or recharge when adapting to a stressor for extended periods. 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, as opposed to “acute stress,” which is temporary. 

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: 

1. The hypothalamus acts as a link between the brain and the autonomic nervous system. 
2. The pituitary gland releases communication hormones when commanded by the hypothalamus. 
3. 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. 

Why chronic stress can be dangerous 

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

• Heart 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 someone you know is struggling or in crisis, help is available. Text or call 988 or chat 988lifeline.org. Support is available 24/7. If you are experiencing trauma, support is available.

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 stress management steps you can take to prevent the worst effects of chronic stress, including a strain on mental resources and brain function.

• 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 essential. Limit how much is on your plate in your personal and professional life 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 to benefit your immune system and overall health. 

Can therapy help with chronic stress? 

If your stress is overwhelming, you might 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 typical stressors and problems in your life that may be increasing your stress.

If your life is already particularly stressful, online therapy may be a more convenient option. Meeting with a therapist from home eliminates time you might have spent commuting to and from in-person appointments and allows you to engage from a place where you feel comfortable. Although online therapists administer psychotherapy remotely, evidence suggests that it may effectively treat mental health challenges like stress, depression, and anxiety. 

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