The science of how stress really affects you.

Stress is a wily beast. Try to get a good look at it, and it slips into the underbrush. And there’s also more than one species. There’s good stress and bad stress. Acute and chronic. Minor and severe. What one stress study reports, another refutes. But one thing is certain: stress can influence how you think and feel and perform in a thousand different ways.

Stress starts in your brain’s limbic system, which is a set of structures that takes the raw data collected by your senses and converts it into an emotional response, according to says Christopher Fagundes, PhD, an assistant professor of psychology at Rice University.

When your limbic system catches wind of some sort of external stressor — whether that’s a wild animal chasing you or a demanding boss pushing up your deadline — it triggers the release of various hormones and neurotransmitters, which in turn shift your brain and body into a heightened state of arousal.

“Stress is basically just that — arousal — and we all need at least a little of it to stay focused and to keep our minds engaged,” Fagundes says. That’s why short-lived periods of mild or moderate stress are often described as helpful, or even “ good.” But when stress surges too high or lasts too long, your brain and your body both stumble.

Stress and Your Brain

Stress-related hormones — cortisol, chief among them — disrupt the way your mind stores and retrieves information, according to a 2016 research review from the University of Hamburg in Germany. When you’re a little stressed, your recall may take a hit while your ability to retain new information seems to be bolstered. (This explains why you blanked on your coworker’s name during your presentation, but you remember, in excruciating detail, her every comment or criticism afterwards.) But when stress soars during a traumatic situation — a car accident, for example — you may only remember fragments of the event. Researchers refer to this as “flashbulb mode.”

The effect stress hormones have on your decision-making is also a mixed bag. When stress first takes hold, a jolt of the hormone norepinephrine can enhance your ability to make quick choices that mitigate risk, according to a 2013 study in the journal Behavioural Brain Research. But when stress lingers, high levels of the hormone cortisol can lead to poorer, less prudent decisions. Like a marathoner who breaks into an all-out sprint at the sound of the starting pistol, your brain grows increasingly prone to missteps. A 2016 study from Dutch and German researchers suggests stress may shift cognition away from high-level processes and into what may be best described as its “get shit done” mode. You’ll do or delegate what’s required to take care of the business at hand, but your brain’s ability to handle complex tasks or long-view thinking may be hampered.

When it comes to your mood and stress, things get even trickier. For some, stress can be motivating — increasing the zeal with which they you attack a task. Some people can step onto an athletic field or behind a podium and perform at their very best, seemingly spinning stress into fuel, not fear. But for others, stress is crippling. A 2014 study in the Journal of Neuroscience concluded that, for some, stress creates hyperactivity in a part of the brain — the medial prefrontal cortex — that has been linked with anxiety and depression. There’s also research that suggests stress hinders your ability to control your emotional responses. This may help explain why, when you’re stressed, you go from placid to furious at the drop of a hat, or a family member’s innocent remark.

Stress Below Your Neck

Understanding how stress affects your body requires a little primer on your immune system.

When your body sustains an injury or infection, your immune system sends its army of white blood cells and pro-inflammatory proteins to isolate and attack the threat, according to Firdaus Dhabhar, PhD, a stress researcher at the University of Miami. But it takes time for these immune system warriors to circulate and arrive at the injury site. So to cut down on that travel time, your immune system mobilizes its forces not just in response to injury, but in anticipation of injury, says George Slavich, PhD, director of the Laboratory for Stress Assessment and Research at UCLA.

This is where stress comes into play.

“Animals only mount a biological response to stress when danger is actually present,” Slavich says. “But humans have the ability to manifest danger in their minds even when it’s not present.” When we do this, our system increases immune activity just in case that imagined threat leads to real injury, he explains.

Another curious thing: the human body can initiate this proactive immune response even if the cause of our stress isn’t a physical threat. “If it’s Tuesday and you have a meeting with a conflictual boss on Friday, you have the ability to mount this immunologic response all week when thinking about the boss,” Slavich says.

In those cases, your brain knows that your cranky manager isn’t going to physically attack you. So why does your body ramp up its defenses? Slavich says human beings are social animals. For hundreds of thousands of years, our ancestors found safety in numbers and in shared resources. “Social isolation, in that context, would lead to a loss of protection and exposure to physical danger,” he says. So, hypothetically, anything that threatens a human’s social standing or relationships — whether it’s a lost job, an impending divorce, or a loved one’s illness — can result in stress and immune system activation, he says.

When stress gooses your immune system into action, immune cells flood your blood and soon set up shop in all the places your body is most likely to encounter an injury — namely your skin, the lining of your gut, your lungs, your liver, and your lymph nodes, Dhabhar says. While all that immune activity can be protective if you’re actually injured, it can cause problems if you’re not.

One example: In your skin, stress hormones like cortisol crank up oil production and cell turnover, according to Adam Friedman, MD, an associate professor of dermatology at George Washington University. A prolonged uptick in stress-related hormone activity could lead to acne breakouts, flushing, and other skin reactions, plus thick or brittle nails and hair loss, he says. Research from the Netherlands has also shown that surging levels of stress hormones can promote constipation and gut irritability, especially for people already suffering from GI disorders.

If chronic stress keeps your immune system in this state of hyperactivity for weeks, months, or even years, that can lead to “dysregulated” immune function and premature immune cell aging, Dhabhar writes in a 2014 paper on the effects of stress on immune function.

“Basically, your body becomes resistant to cortisol, and inflammation is the consequence,” Rice University’s Fagundes explains. A little inflammation is a good thing; it and can help your body fend off infection or disease, or heal wounds. But research has linked long-term, system-wide inflammation to cancer, heart disease, autoimmune disorders, and other life-threatening diseases, he says. A 2009 study from Columbia University found stress hormones can disrupt your nervous system in ways that fuel insomnia and overeating.

There’s a Lot More to Discover

According to UCLA’s Slavich, the scientific community’s understanding of how deeply stress affects our minds and bodies is still evolving. “We’ve only understood that stress can increase inflammation and influence the immune system for the last decade or so,” he says. Because that understanding is so new, it’s still atypical for health care providers to try to gauge patients’ stress levels. Stress researchers also haven’t yet agreed on good methods for measuring long-term stress exposure.

When it comes to understanding stress and its effects, we’ve only just yanked off the blindfold. What we’re seeing now is blurry. It will take more time and research before our view of stress and its health impacts comes into focus.

In the meantime, knowing the ways stress can affect you — for better or worse — is all the more reason to tune in to your own levels day-to-day and long term.

Originally published at