What Is the Fight-or-Flight Response?

Experiencing Physical Symptoms in Response to Stress

fight or flight response illustration

Verywell / Joshua Seong

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The fight-or-flight response, also known as the acute stress response, refers to the physiological reaction that occurs when in the presence of something mentally or physically terrifying. This response is triggered by the release of hormones that prepare your body to either stay and deal with a threat or to run away to safety.

The three stages of fight-or-flight are:

  • The alarm stage: During this stage, the central nervous system is ramped up, preparing your body to fight or flee.
  • The resistance stage: This is the stage in which the body attempts to normalize and recover from the initial elevated fight-or-flight response.
  • The exhaustion stage: If the first two stages occur repeatedly over time, such as when under chronic stress, this can cause the body to feel exhausted and begin to break down.

Evolution of the Fight-or-Flight Response

The term "fight-or-flight" represents the choices our ancient ancestors had when faced with danger in their environment: to either fight or flee. In either case, the physiological and psychological response to stress prepares the body to react to the danger.

In the 1920s, American physiologist Walter Cannon was the first to describe the fight-or-flight response. Cannon realized that a chain of rapidly occurring reactions inside the body helped to mobilize the body's resources to deal with threatening circumstances.

Today, the fight-or-flight response is recognized as part of the first stage of Hans Selye's general adaptation syndrome, a theory describing the stress response.

What Happens During the Fight-or-Flight Response

In response to acute stress, the body's sympathetic nervous system is activated by the sudden release of hormones. Fight-or-flight response hormones include adrenocorticotropic hormone and corticotropin-releasing hormone.

These hormones cause the sympathetic nervous system to stimulate the pituitary gland and adrenal glands. This triggers the release of catecholamines, including adrenaline, noradrenaline, and cortisol.

This chain of reactions results in an increased heart rate, blood pressure, and breathing rate. Your body can stay in fight-or-flight for 20 to 60 minutes after the threat is gone, which is how long it takes for the parasympathetic nervous system to return it to pre-arousal levels.

The sympathetic nervous system promotes the fight-or-flight response while the parasympathetic nervous system helps calm the body once the threat is gone.

Physical Signs of a Fight-or-Flight Response

Physical signs that can indicate that your fight-or-flight response has kicked in include:

  • Dilated pupils: In times of danger, the body prepares itself to become more aware of its surroundings. Dilation of the pupils allows more light into the eyes, resulting in better vision of your surrounding area.
  • Pale or flushed skin: During fight-or-flight, blood flow to the surface areas of the body is reduced while flow to the muscles, brain, legs, and arms is increased. Paleness or alternating between a pale and flushed face as blood rushes to the head and brain is common. The body's blood clotting ability also increases to prevent excess blood loss in the event of injury.
  • Rapid heart rate and breathing: Heartbeat and respiration rate increase to provide the body with the energy and oxygen needed to fuel a rapid response to danger.
  • Trembling: The muscles tense and become primed for action, which can cause trembling or shaking.

You can probably think of a time when you experienced the fight-or-flight response. When faced with something frightening, you can feel your heartbeat quicken, you may start breathing faster, and your entire body becomes tense and ready to take action.

Impact of the Fight-or-Flight Response

There are both benefits and drawbacks to the fight-or-flight response.

Benefits of Fight-or-Flight

The fight-or-flight response plays a critical role in how we deal with stress and danger in our environment. When we are under threat, the response prepares the body to either fight or flee. By priming your body for action, you are better prepared to perform under pressure.

The stress created by the situation can actually be helpful, making it more likely that you will cope effectively with the threat. This type of stress can help you perform better in situations where you are under pressure to do well, such as at work or school.

Some experts suggest that the flight-or-flight response may even provide benefits when the urge to fight others in an attempt to harm them is, instead, transformed into the urge to fight to protect them. This may be beneficial when the fight-or-flight response is triggered by negative emotions such as anger and fear.

And in cases where the threat is life-threatening, the fight-or-flight response plays a critical role in your survival. By gearing you up to fight or flee, the fight-or-flight response makes it more likely that you will survive the danger.

Drawbacks of Fight-or-Flight

While the fight-or-flight response happens automatically, that doesn't mean that it is always accurate. Sometimes we respond in this way even when there is no real threat.

This is because the fight-or-flight response can be triggered by both real and imaginary threats. Phobias are good examples of how the fight-or-flight response might be falsely triggered in the face of a perceived threat.

Constantly being in a state of fight-or-flight, such as when facing repeated stressors, can also be harmful to your health. Chronic stress can increase your risk of:

  • Chronic fatigue
  • Depression
  • Gastrointestinal issues
  • Headaches and migraines
  • Heart attack and stroke
  • High blood pressure and cholesterol levels
  • Metabolic disorders, such as diabetes and obesity
  • Poor immune function
  • Reproductive and sexual dysfunction
  • Worsened breathing problems, such as those related to asthma

Is Anxiety a Fight-or-Flight Response?

Some research indicates that the body's desire to fight or flee can increase a person's risk of developing an anxiety disorder, making them more vulnerable to this type of mental health condition.

Examples of the Fight-or-Flight Response

The fight-or-flight response can happen in the face of imminent physical danger, such as when encountering a growling dog during your morning jog. It can also be the result of a psychological threat, such as preparing to give a big presentation at school or work.

Another example of the flight-or-fight response is if a person who is terrified of heights has to go to the top floor of a skyscraper to attend a meeting. Their body might go on high alert, with their heartbeat and respiration rate increasing. If the response is severe, it can lead to a panic attack.

How to Calm a Fight-or-Flight Response

Understanding the body's natural fight-or-flight response is one way to help cope with such situations. When you notice that you are becoming tense, you can start looking for ways to calm down and relax your body.

Ways to calm the fight-or-flight response include:

Psychology and the Fight-or-Flight Response

The stress response is one of the major topics studied in the rapidly-growing field of health psychology. Health psychologists are interested in helping people find ways to combat stress and live healthier, more productive lives.

By learning more about the fight-or-flight response, psychologists can help people explore new ways to deal with their natural reactions to stress.

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Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading

By Kendra Cherry
Kendra Cherry, MS, is an author and educational consultant focused on helping students learn about psychology.