Fight-or-Flight: How Your Body Handles Stress (2024)

By:Jessica Monge, Health & Wellness Writer

You’re walking down the street, busy thinking about your to-do list, when you hear, “Watch out!” Suddenly, without fully processing what’s happening around you, your heart rate quickens, your blood pressure rises, and your muscles tighten as adrenaline rushes through your system.

What’s triggered this dramatic reaction, known as the “fight-or-flight response”? Your body is preparing to protect you from a situation it perceives as life-threatening, be it a saber-toothed tiger, a car swerving in your direction, or a football headed for your face. (Of course, intellectually you probably know that compared to a hungry tiger, an errant football is unlikely to do much damage…but that initial, hard-wired reaction is a built-in survival response.) Whether your first instinct is to fight back, flee or, like a rabbit sensing a predator, simply freeze in place, the ultimate goal is survival.

So what’s the science behind this immediate, physical reaction to threats, danger and even non-threatening situations? And why are some of us more likely to be fighters than freezers or fleers? Here’s the lowdown on how your stress response works, plus how to prevent moments of temporary panic from becoming a long-term threat to your health.

What does flight or fight mean?

The “fight-or-flight response” is an old-school term used to describe acute stress response and how your body reacts to anything you perceive as a threat to your well-being. In fact, the term was first used back in the early 1900s. (That’s correct, 100 years ago!) Modern psychology experts have found it to be incomplete in describing all the different ways people can react when facing an immediate threat. That’s why, nowadays, your stress response is referred to as the fight-flight-freeze response, which offers a more nuanced description of the physiological reaction people experience in a tense situation.

• Fight means you respond to the threat with a surge of energy, aggression or even anger.
• Flight refers to the instinct to run away, hide, protect yourself—you may also be restless and fidgety.
• Freeze is exactly what it sounds like—you remain motionless, in dread of what’s about to happen.

Whether you fight, flight or freeze, it all begins the same way: in the brain, when you observe something about your surroundings that’s “off.” Your brain then sends a signal to a part of your nervous system that’s key to how you respond to stress, known as the sympathetic nervous system—you know, that nerve-wracking, palms sweating, heart-pounding in your ears we all know and love.

Why do humans have a fight or flight response?

The fight or flight response is a biological mechanism that humans and animals depend on for survival. Whether your body gravitates to a fight response, flight response or freeze response, the physiological reactions you experience are designed to keep you alive. This dates back to the days when humans roamed the Earth alongside larger predators and could get eaten (or simply starve) if they didn’t act quickly.

Today, of course, our stress factors usually don’t have the same life-or-death consequences as having to forage for food, seek shelter and outrun predators. Still, our bodies don’t understand that a looming deadline is not as serious of a threat as what our ancestors felt when they needed to (literally) run for their lives.

Here's where proper stress management and prioritizing selfcare to reduce anxiety and promote relaxation come in. Remember, when you stay in that fight-flight-freeze mode longer than you should, it can lead to chronic stress, which is detrimental to your health.

How does fight or flight affect the body?

Upon perceiving a threat, your stress response gets triggered by two components of your body: your sympathetic nervous system and your hypothalamic-pituitary-adrenal axis, or HPA axis for short. Together, your HPA axis and your sympathetic nervous system activate your adrenal glands, which have an immediate response and pump epinephrine (you know it as adrenaline) into your bloodstream.

Once epinephrine is coursing through your system, it causes many changes in your body and the familiar physiological rollercoaster starts:

• Dilated pupils—Your pupils open up to take in more light to reach the back of your eyes, sharpening your vision so you can see better.
• Your heart rate and blood pressure increase—This means your heart is pumping blood with more force and at a faster rate. And by now, you’re also breathing quickly and heavily, which helps push newly oxygenated blood and nutrients to your brain, organs and major muscle groups.
• Muscles tighten—The rush of blood to your skeletal muscles keeps you at the ready for anything that comes up, such as pressing the brakes of your car when someone swerves into your lane, or ducking when someone lobs a ball in your direction (unless you freeze and do nothing, and the football hits you in the nose, Marsha Brady style).
• Energy availability—The adrenaline surge also triggers a spike in blood sugar and fats to ensure there’s enough energy available at a moment’s notice.
• Prioritizing survival—The physiological changes allow the body to prioritize survival over other biological processes—forget digesting when you need to fight over food or jump out of the way. (If that well-known saying “soil your pants” comes to mind, you understand it’s the body prioritizing a “lighter” getaway.)

As you can see, there’s a lot of work that happens behind the scenes when we’re experiencing acute stress, though that stress reaction may feel like single event—when you can feel combative (ready to fight) or avoidant (adios!), or freeze.

Which hormone is responsible for fight or flight?

Cortisol often steals the spotlight when talking about stress, since it's been much-discussed for its relationship to chronic stress. But it's epinephrine (also known as adrenaline) that is responsible for the immediate, fast-acting, rapid heartrate and breathing, fight or flight response. A related hormone, norepinephrine, has a similar impact on the acute stress response. Both of these have relatively short-lived effects on the body. When the danger has passed, your “happy hormones” come into play, helping you feel calm and relaxed again.

Both epinephrine and norepinephrine are involved in an immediate response; cortisol is responsible for a longer duration of your fight-flight-freeze response. And it’s cortisol levels that tend to stay high long after we’re done with our day and ready for bed.

Pro tip: If your body is still wound up from your day, it could be due to elevated cortisol levels, possibly in part because of lack of quality sleep.

What are the 3 stages of stress?

Again, keep in mind that everyone experiences stress in their unique way. But in general terms, there are three ways the body expresses stress.

1. Acute stress—As mentioned above, this is your immediate, ready-to-act, take-flight or freeze response.
2. Episodic acute stress—When we don’t address long-simmering stress, even minor provocations can leave us frazzled and unsettled. Whether it's missing a relatively unimportant deadline, or the noise of your teenagers fighting yet again over a video game, little things can become major things fast.
3. Chronic stress—This is the prolonged stress that wears and tears at our health, increasing the risk for more serious health concerns, including anxiety disorders and ongoing inflammation; it can also affect the health and structure of blood vessels and other tissues throughout the body. Additionally, unmanaged stress could put you at risk for unhealthy weight gain; we might ignore the low-level physical stress that our bodies hold on to after the acute stress has passed and indulge in eating comfort food to cope. To add insult to injury, long-term stress can contribute to the silver strands on the top of your head and deepen the creases of your laugh lines.

Is FOMO part of the fight or flight response?

No. They are very different terms. FOMO, or fear of missing out, is an acronym coined back in 2004 and is used to refer to people’s common reactions to social media. (Certainly many of us can relate to that dreaded sensation elicited by curated pictures of people having more fun than us, sipping martinis by the pool on some faraway retreat while we stare at our phone screens from inside a windowless office.)

But while FOMO is not the same physiological response you experience when you are in danger, it can be a source of stress and anxiety for people who experience it.

How can you avoid the fight or flight response?

We don’t want to get rid of our fight or flight response—it will come in handy when you do need to protect yourself from an actual life-or-death threat! That being said, there are ways to promote a more balanced fight-or-flight response.

Here are four tips to help you put all that pent-up energy to work and promote a healthy stress expression.

• Get your body moving—You know exercise is terrific for your brain, and it also helps manage blood sugar levels and support a healthy weight. But nothing feels better than a good sweat session when you’re having “one of those days.” Whether you dance, bike or lift weights, having a regular exercise routine can help keep your stress levels in check. Aim for 30 minutes a day at least five days a week, and combine cardio with resistance training to target and tone different muscle groups.
• Catch those ZZZs—If you wake up tired, you may be sleeping, but you’re not getting restful sleep. There’s nothing fun about dealing with a crying toddler or meeting a deadline when you feel on edge for lack of quality sleep.
• Cultivate a “zen” state of mind—Practice mindfulness, or the habit of living in the present moment. Spending time in nature, yoga or meditation can help you ground yourself and better handle stressful situations. Pro tip: Start your days with green tea; the amino acid l-theanine is the active compound in this traditional soothing drink, and it’s known for promoting calming feelings and relaxation. If you decide to have a relaxing cup of green tea later in the day, remember to opt for decaffeinated tea.
• Baby your belly—Your gut and mind are intimately linked, and ensuring you have a balanced gut microbiome has been shown to help with how your body handles depression, anxiety and stress. Adding fermented foods (such as sauerkraut or kefir) to your meals or probiotic formulas is an easy way to help the friendly-gut bacteria thrive!

References

• Gupta, Mayank et al. “Fear of Missing Out: A brief Overview of Origin, Theoretical Underpinnings and Relationship with Mental Health.” World J Clin Cases. July 2021, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8283615/
• Roelofs, Karin. “Freeze for Action: Neurobiological Mechanisms in Animal and Human Freezing.” Phils Trans R. Soc. Longd. B. Biol Sci., April 2017, https://pubmed.ncbi.nlm.nih.gov/28242739/
• Ropeik, David. “The Consequences of Fear.” EMBO Rep., October 2004, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1299209/
• Tindle, Jacob et al. “Neuroanatomy, Parasympatheic Nervous System.” StatPearls, November 2021, https://www.ncbi.nlm.nih.gov/books/NBK553141/
• Warell, Margie. “Are You Worrying About the Wrong Things? How to Discern Real Threats From Imagined Ones.” Forbes, April 2017, https://www.forbes.com/sites/margiewarrell/2017/04/01/are-you-worrying-about-the-wrong-things-how-to-discern-real-threats-from-imagined-ones/?sh=2ababd94247c
• “Adrenal Glands.” Johns Hopkins Medicine, https://www.hopkinsmedicine.org/health/conditions-and-diseases/adrenal-glands
• “Exercise for Stress and Anxiety.” Anxiety & Depression Association of America, https://adaa.org/living-with-anxiety/managing-anxiety/exercise-stress-and-anxiety
• “Norepinephrine & Epinephrine.” University of California, San Francisco, https://www.stressmeasurement.org/norepinephrine-epinephrine
• “Stress Won’t Go Away? Maybe You Are Suffering From Chronic Stress.” American Psychological Association, October 2019, https://www.apa.org/topics/stress/chronic
• “Sympathetic Nervous System (SNS).” Cleveland Clinic, https://my.clevelandclinic.org/health/body/23262-sympathetic-nervous-system-sns-fight-or-flight
• Waltman, Scott Harris et al. “Theoretical Overlap and Distinction Between Rational Emotive Behavior Therapy’s Awfulizing and Cognitive Therapy’s Catastrophizing.” Mental Health Review Journal, January 2019, https://www.emerald.com/insight/content/doi/10.1108/MHRJ-07-2018-0022/full/html
• “Understanding the Stress Response.” Harvard Health Publishing, July 2020, https://www.health.harvard.edu/staying-healthy/understanding-the-stress-response

Scientifically Reviewed By: Michael A. Smith, MD

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