Stress activates the "fight-or-flight" response when we face threats, a reaction that can help keep us alive.

Why does the body have a stress response?

When encountering a stressful situation, the human body typically goes into what is known as "fight-or-flight" mode. Because it evolved as a survival mechanism, the biochemical response enables people and other mammals to react quickly to life-threatening situations. The carefully orchestrated yet near-instantaneous sequence of hormonal changes and physiological responses helps someone to fight the threat off or flee to safety.

Stress-induced adrenaline can trigger a 'hysterical strength' response

The stress response is a powerful ancient mechanism designed to maximize human survival—it can even result in superhuman strength. The adrenal glands are located just above the kidneys, and stress-induced adrenaline release causes more blood (and therefore more oxygen) to flow to your muscles, increasing performance.

Our ancient fight-or-flight response may contribute to modern ailments

Many common modern diseases humans struggle with may in fact have their origins in our ancient fight-or-flight stress response. Long-term effects of the stress hormones cortisol and adrenaline—in this case, triggered by things like workplace stressors—can wreak havoc on the delicate internal balance of our organ systems.

Chronic stress affects nearly all parts of the body

Stress is our body’s internal mechanism to deal with changes in our internal balance. As such, the stress response affects nearly every organ system through a cascade of both fast and slow hormonal changes. While short-term stress can be adaptive, long-term stress may cause serious health issues.

The biology of stress in your body

Stress is a normal human response that has evolved over millions of years to handle changes or threats in our environment. This article is a helpful overview of the biological basics of this response. While it is not harmful to our physiology in the acute setting, chronic stress can lead to damaging changes in the human body over many years.

The second phase of acute stress: the 'slow' response

The body's reaction to acute stress involves two responses: fast and slow. The first occurs immediately, with the central nervous system triggering the release of adrenaline. The second releases cortisol, which elevates blood sugar and blood pressure and restricts nonessential functions like digestion and the immune system.

Too little stress can also harm our health because mild or moderate stress—followed by recovery—helps make us resilient.

Stress and the brain

While an acute stress response is a normal bodily function, the effects of chronic stress can be extremely damaging to the human body. This is particularly true with regard to the brain. This article explores the effects of stress on the human brain, including how chronic stress may lead to psychological conditions such as depression and memory loss.

The two phases of stress: fast and slow

The physiological response to acute stress generally involves two phases—the "fast" response in which adrenaline is released, and a second "slow" response in which cortisol is released. This technical resource reviews what happens in the body during each phase.

Stress can be contagious—and scientists want to learn more about it

Researchers have shown that being around someone who is stressed can trigger a stress response in your body, such as elevated cortisol levels and elevated heart rate. One way this was recently studied was by having people watch stressful activities, like a recorded job interview or solving challenging math problems, and then sampling hormones in observers' spit.

Fear (and stress) can be contagious via pheromones secreted by the body

While seeing someone else in a panicked state may induce a stress response, researchers have found stress can be literally contagious—chemicals contained in sweat and other secretions can trigger stress hormone release in others. Theories suggest this feature is an evolutionary adaptation to protect groups from danger.

How do anxiety and stress differ?

This article explains that though “stress” and “anxiety” are often used interchangeably, there are distinct differences between the two. Stress is defined as the body's response to an external trigger and can be classified as acute or chronic. Anxiety, however, tends to be triggered internally by excessive thoughts and judgement. Whereas stress disappears when the trigger is gone, anxiety tends to stick around. If left unchecked, both can escalate into more severe mental health conditions.

Prolonged stress impairs the prefrontal cortex

Burnout isn't just a feeling—it physically affects the brain. Prolonged stress impairs regions of the brain responsible for decision-making, emotional control, memory, and more. It can also lead to chemical imbalances, like reduced dopamine and norepinephrine levels, that worsen these effects.

Stress affects different animals in different, but useful, ways

Animals feel stress when they experience actual dangers—such as a zebra chased by a lion. Humans often feel stress from worries, memories, or even thoughts about problems that may occur in the future. For this reason, animals tend to experience stress in short, intense bursts. Conversely, people can feel stressed for long periods, which can eventually be harmful to their health.

Short-term cortisol spikes can boost the immune system

Elevated acute levels can enhance the immune system's ability to fight off infection or respond to injury. Chronic heightened cortisol levels, however, can lead to inflammation that harms cells and tissues over time.

Consuming true crime media can increase stress and anxiety and create a false sense of danger.

The positives of feeling stressed

Worrying about past events and upcoming challenges is not a pleasant experience, but a reasonable amount of stress can bring a lot of good into our lives. In this episode of "The Happiness Lab" with Dr. Laurie Santos, two psychology experts offer tips for resetting one's relationship with stress. Listen and learn how to make stress a positive tool rather than a debilitating emotion.

How we frame stress—as good or bad—seems to alter how it affects us

This podcast discusses research that indicates stress perception may drastically affect how we respond to it. In research exploring if our stress is presented as diminishing our health versus if we're told it enhances our performance, it will lead to differences in how successful participants are at performing tasks—with the enhancers doing better.

Some types of stress (eustress) have positive benefits

While many perceive stress as solely negative, stress can in fact be divided into two categories: distress (negative stress) and eustress (positive stress). Moderate levels of stress are positive in that they can boost motivation and promote resilience, which have positive mental health benefits.

How stress affects every organ in the body

If you are a visual learner, this resource is for you. Not only does this article from the World Economic Forum outline the causes of modern stress along with helpful strategies, but they have created an approachable infographic to show exactly how stress manifests throughout our different bodily systems. Pair this visual guide with our other resources to gain a deep knowledge of stress and the human body.

Fearology, or the study of fear, explores the difference between stress and fear

Our brains involuntarily respond to our environment and signal alarm when that isn't always needed, triggering responses that include goose bumps. But understanding fear and how to talk our brains into calming down can improve daily life.

Stress and anxiety may lead to similar symptoms, but stress is a response to external triggers, while anxiety is persistent, and its symptoms won't disappear once an immediate stressor is gone.

Stress contributes to gray hair because when the body experiences stress, the sympathetic nervous system releases specific hormones that influence pigment-producing cells.

Touch deprivation can heighten anxiety and depression

Pacinian Corpuscles are pressure receptors just under the skin that send signals to the vagus nerve in the brain—that's the cranial nerve which regulates involuntary actions like breathing, heart rate, and the general "fight or flight" response. Activating those receptors can slow the heart, decrease blood pressure, and lead to the release of oxytocin and cortisol. The absence of touch, conversely, can promote negative feelings.

How burnout alters your brain

Stress is a normal part of everyday life, and it’s not necessarily all bad. But chronic stress—the kind that leads to burnout—can change the size and functioning of parts of your brain. It can alter the ability to make new brain cells and memories and even potentially modify your DNA.

Even brief physical activity can trigger the release of neurotransmitters that provide mental health boosts.

Cold water swimming can induce positive stress

The tradition of cold water swimming (or taking a cold plunge, or even a cold shower) has been shown to release the same hormones triggered during a stress response. This can have the effect of increasing blood flow, improved mental acuity, and more.

The body produces its own opioids that act on several receptor types throughout the body, triggering the release of dopamine and suppression of noradrenaline, neurotransmitters associated with reward and alertness, respectively.

Grief rewires the human brain

The human brain handles stress and emotional traumas similarly. In response to the emotional stress of a situation like the death of a loved one, divorce, or abuse, the brain may strengthen or weaken connections between nerves to form new neural connections. Over time, chronic stress can diminish brainpower, reducing overall nerve growth and memory to shift resources to enable elevated fear responses and enable humans to survive.

Anxiety can arise at any stage of life and make someone feel unsafe in their mind and body.

Music that builds to a crescendo and then resolves relieves stress more than listening to nature sounds.

Brain conditions and surgery can cause some individuals to feel no fear

Fear is a survival mechanism that originates in the brain's amygdala, triggering the body's fight-or-flight response. However, in modern society, without the same natural dangers, fear can lead to anxiety and mental health issues when unnecessarily triggered. Understanding individuals without fear may help identify new methods to treat anxiety disorders.

Goose bumps are often triggered by emotions

A physiologist and professor of zoology explains that the subconscious release of adrenaline, a stress hormone, causes a contraction of skin muscles. It’s released in several situations, including when humans are cold, afraid, or feel strong emotions. (Some readers may experience a paywall.)

Exercise improves brain blood flow, stimulates neural growth, and more.

Why are humans hooked on horror?

A haunted horror attraction in Denmark is regularly stalked by researchers of the world's only laboratory dedicated to understanding fear's good side. Fear is one of many human emotions that correspond to a physiological response. As fear rises, so do adrenaline, cortisol, and heart and breath rates. As it ebbs, the body is flooded with dopamine, a hormone and neurotransmitter associated with desire, learning, and motivation.

Anxiety is one of the world's most common mental health disorders, causing persistent excessive fear and worry that interferes with daily activities.

Some claim breathwork can improve mental health, help process trauma, and more

Research shows people who practice breathing exercises see a decrease in depression and stress levels, and that such exercises are about as effective at treating PTSD as conventional approaches. Even something as simple as extending exhales can slow one's heart rate and activate the parasympathetic nervous system.

Where do phobias come from?

Scientists say phobias are extreme version of a primitive evolutionary mechanism that tells us when danger is near or we are in a dangerous situation. A number of brain regions work in concert to trigger flight or fight responses, and with some...

Chronic inflammation can cause cellular damage and could lead to cancer

Over time, this cellular defense system can inadvertently damage cells and tissues when it's in this heightened alarm mode over a prolonged period. This occurs because, when immune cells are sent somewhere without a true target, they may attack healthy cells and tissues.

Love and heartbreak trigger powerful, neurochemical-driven changes in the body

The feeling of falling in love floods the brain with dopamine, oxytocin and serotonin, which collectively dull pain and boost immunity. However, the loss of these chemicals during a break-up produces withdrawal-like symptoms and heart issues, such as high blood pressure.

Just a 10-minute mental health break can yield benefits

The US CDC offers recommendations for alleviating stress in daily life. Short 10-minute breaks can significantly improve mental health, especially when used for activities like deep breathing, dancing, or writing down things you are grateful for. Building meaningful relationships, termed "social connectedness," can also alleviate stress and promote resilience.

Self-care can't fix burnout on its own

Steps such as exercise, breathing, mindful eating, and spending time with friends, can help alleviate the fight-or-flight mode response of the body to alleviate stress, but they don't fix the stressors causing the burnout. To address those, workplaces may need to consider how to better manage workloads and duties.

Exercise releases chemicals that enhance cognitive function

Neurotransmitters like dopamine, serotonin, and norepinephrine, along with increased brain-derived neurotrophic factor levels, enhance a wide range of brain functions. New research demonstrates a direct link between movement and numerous cognitive benefits, including memory, learning, and stress resilience.

Panic attacks are intense fear episodes that often occur without a clear trigger

Unlike typical fear responses to real danger, panic attacks can mimic serious health problems, such as heart attacks. Sweating during a panic attack may seem random, but it's a leftover survival mechanism that made it easier for our ancestors to escape by slipping out of an attacker’s grasp.

The limbic system drives emotion, memory, and survival instincts in the brain.

This interconnected group of brain structures—including the amygdala, hippocampus, thalamus, and hypothalamus—processes emotional responses, regulates bodily functions, and plays a key role in memory and learning.

Easy resets for stress reduction

Individual solutions for burnout, often called “self-care,” can be helpful for managing stress. Harvard researcher Aditi Nerurkar’s 2024 book The Five Resets details a road map for burnout recovery. In this interview she suggests, among other tactics, gaining focus on what matters the most in one’s life, taking breaks from both work and the internet, and making time for practices that strengthen the mind-body connection.

Why so many people love roller coasters even though they’re scary

When a threat arises, it triggers our bodies to go into fight-or-flight mode and prepare for danger. However, when no obvious threat to our safety is present, this natural high can become enjoyable. Some people are more likely to enjoy these thrills based on factors like individual brain chemistry or physical health.

The 10 top tips a psychotherapist offers her patients with anxiety include "you will not die from anxiety" and "anxiety is just trying to protect you."

What happens to your brain when you burn out?

You've probably heard of burnout, also known as the feeling of exhaustion that happens after a long period of being overwhelmed or stressed. It's often associated with work and careers, but other parts of life, like parenting, can cause burnout, too. Scientists are figuring out what happens, biochemically speaking, in the brain when burnout hits—and spoiler alert, it includes a neurotransmitter called glutamate. Watch this video to learn more.

The brain will attempt to rest itself in periods of chronic sleep deprivation

Skimping on sleep lengthens reaction times and blunts decision-making skills. At a certain point, the brain will try to sneak sleep where it can, shifting sections offline even as you remain awake. Going without sleep raises blood pressure, undermines the immune system, and increases one's risk of dementia.