What Is the Fight-or-Flight Response?

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.

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.