What Is the Fight or Flight Response? Everything to Know

Medically Reviewed By Karin Gepp, PsyD
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The fight-or-flight response, or stress response, occurs when a stressful situation activates stress hormones. It is an automatic response as the body prepares to face or run away from real or perceived danger. During the fight-or-flight response, the body releases a rush of adrenalin, increasing the heart rate and blood pressure. This can be a response to an environmental threat, such as oncoming traffic. It could also be a response to a threat to your psychological well-being.

Read on to learn more about the fight-or-flight response. This guide includes information about how the fight-or-flight response works, what happens to the body, and more.

When does the fight-or-flight response happen?

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The fight-or-flight response happens when you perceive danger, either an environmental threat or a threat to your psychological well-being.

Environmental threats are dangers that can cause you physical harm. These dangers, such as oncoming traffic or a physical attack, cause you to either fight back or flee the situation.

Psychological threats are stressful situations that can trigger the fight-or-flight response. They may threaten your happiness, well-being, or sense of security.

Examples of psychological stresses that can trigger the fight-or-flight response include:

  • being out of work or feeling pressure in the workplace
  • having relationship difficulties
  • going through a divorce
  • having financial problems
  • experiencing an injury
  • having an illness
  • losing somebody close to you

How does the fight-or-flight response work?

The fight-or-flight response originates in the brain.

  1. When you perceive a stressful situation or danger, the amygdala, associated with emotional responses, sends a message to the hypothalamus.
  2. The hypothalamus activates. This gland is responsible for triggering the release of hormones. 
  3. The hypothalamus sends a message to the adrenal glands in the sympathetic nervous system, which release stress hormones, including adrenaline and cortisol. 
  4. You experience the fight-or-flight response as the body prepares to respond to the perceived threat.

Learn more about the hypothalamus.

What happens to the body during the fight-or-flight response?

When the hypothalamus releases stress hormones, your body prepares to either run away from the danger or fight it.

Physical symptoms you may experience with the fight-or-flight response include:

  • racing thoughts as you evaluate the situation and decide whether to fight or flee
  • changes in vision, such as tunnel vision or sharper vision, as you focus on the danger
  • dry mouth due to the digestive system shutting down and directing energy wherever necessary to fight or flee
  • nausea as a result of blood directing away from the digestive system and toward the muscles
  • quickened breathing to take more oxygen into the body, which helps the body to run or fight
  • dizziness or lightheadedness due to an increase in oxygen
  • increased heart rate to send more blood to your muscles and aid in running or fighting
  • tense muscles as the body prepares to fight or flee
  • urge to urinate as the bladder can relax in response to stress
  • cold hands as the blood moves away from vessels in the hands, moving toward muscles instead
  • sweaty palms as the body sweats to keep itself cool, which can help with survival

What is the freeze response?

The freeze response typically occurs before your body enters into the fight-or-flight response. This is when you focus on the threat but are not yet ready to fight or flee from the situation.

You will leave the freeze response once your body releases the stress hormones and activates the fight-or-flight response.

Why is the fight-or-flight response important?

The fight-or-flight response is important as it serves to protect you in potentially dangerous situations.

Historically, fear triggered the fight-or-flight response when faced with a serious threat, such as an attack from a wild animal. The body would prepare itself to fight off the animal or run away from danger to somewhere safer.

Today, the fight-or-flight response can help protect you from oncoming danger, such as an attack or other physical harm. It can also help you deal with stressful situations.

Overactive fight-or-flight response

It is important to note that the fight-or-flight response can be unhelpful in some situations. For example, having an overactive fight-or-flight response before a job interview or during a test can make you feel anxious. This may be especially true if you cannot physically run away from the situation.

Managing stress can help you better manage an overactive fight-or-flight response. This can reduce the risk of your body perceiving certain situations as a threat. In turn, that reduces the likelihood of triggering the fight-or-flight response in situations without real danger.

How can I manage stress?

Taking steps to manage stress can better equip you to deal with stressful situations. These can include:

  • eating a healthy, balanced diet
  • exercising regularly
  • concentrating on your breathing
  • trying to focus on positive thoughts
  • using visualizing techniques to overcome negative feelings or emotions
  • speaking with a mental health professional or attending therapy, such as cognitive behavioral therapy (CBT)

Discover more ways to treat or manage stress.

When should I contact a doctor?

Contact your doctor if you frequently experience stress or anxiety. They can refer you to a mental health specialist who can help you learn some coping mechanisms. These mechanisms, including CBT, can help you manage the physical symptoms of the fight-or-flight response.

Depending on the cause of your stress, they may also refer you to a specialist to help you manage it. For example, your doctor may refer you to a bereavement counselor if you have lost a loved one.

Our Stress Appointment Guide can help you to prepare for your appointment.


The fight-or-flight response is an automatic response that helps protect you from danger. The body can trigger this response when it detects a physical or psychological threat to your well-being.

When the body releases stress hormones and prepares itself for defense, you may experience lightheadedness, quickened breathing, and increased heart rate, among other symptoms. This response may be useful for quickly getting you to safety in some situations. However, it can also occur when there is no real danger.

Contact your doctor if you have feelings of anxiety or concerns about the fight-or-flight response. They can refer you to a specialist for tips to help manage stress or stressful situations.

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Medical Reviewer: Karin Gepp, PsyD
Last Review Date: 2022 Jul 22
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