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Your heart rate speeds up, your breathing quickens. Your muscles tighten. Your stomach ties itself in knots. All of these changes are symptoms of the condition called stress.

When animals, including humans, are under acute stress, their bodies respond with a powerful neurochemical chain reaction. Glucose, the fuel for our cells, is released into the blood from storage sites in our body, notably the liver. The elevated heart rate increases circulation of the energy-enriched blood to the muscles. Any long-term body processes not immediately necessary, such as digestion, growth, and reproduction, are slowed down. Immune defenses are enhanced, ready to respond to bodily injury, and our senses are sharpened.

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The major purpose of this response, says psychiatrist and stress researcher Kristen Aschbacher, “is to help redirect energy away from less critical functions in order to devote them to survival functions.” Stress gets you ready to react.

But a recent study published in the journal Psychoneuroendocrinology shows that the stress response is not just experienced by those directly in a crisis: It can be contagious. You can catch it from seeing other people under stress, even if you’re watching a stranger on a video screen. This phenomenon is called “empathetic stress.” 

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The study looked at pairs of total strangers along with romantically involved couples that had been together for at least six months. One person from each pair was subjected to the Trier social stress test, where they were given a fictitious job interview, then asked challenging arithmetic questions in front of a panel of supposed “behavior analysts.” The other member of the couple simply observed the test, either via a one-way mirror or a video transmission. 

The set-ups were designed to simulate real-life situations that could potentially induce empathetic stress: observing a real person nearby, and virtually. “Given the omnipresence of television today and the fact that often stressful information is communicated via TV, we were specifically interested in whether a virtual confrontation with stress would be strong enough to elicit a response,” says Veronika Engert, one of the study’s five co-authors. 

The researchers made sure the onlookers knew that they would not be subjected to the test themselves, so as to ensure that they spent their time observing and not worrying that they would suffer the same fate. To measure stress levels, the researchers measured the amount of the stress hormone cortisol in the saliva of both the test-taker and observer at different points throughout the session. 

All but 5% of the participants taking the stress-inducing test showed signs of stress, demonstrated by an increase in cortisol. Overall, 26 percent of all the observers also experienced “empathetic stress,” just from watching their partner take the test.  As you would probably expect, there was a big discrepancy between the romantic and strange couples. 

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One in 10 of the observers felt empathetic stress from watching a stranger struggle, but if the observed person was a loved one, the percentage quadrupled. “The reason may be that we have a better understanding of the cues, both non-verbal and verbal, signaling stress from our loved ones,” explains scientist Tony Buchanan, who was not involved with this study but independently studies empathetic stress. “We are experts at detecting emotional states in those we live with, but it most likely takes time and experience to understand people we’ve just met.” The very fact that empathetic stress did show up at all between two strangers came as a surprise, says study co-author and neurology research fellow Franziska Plessow. 

So why does stress reflect onto other people? Plessow says that they can only speculate. The researchers write that “being in tune with another individual may have an adaptive evolutionary purpose”—that is, a survival advantage—because it allows us to gain information about whatever is causing the suffering. “If one rat, monkey, or human is under stress, the others in the group may need to pay attention in order to understand why that individual [is stressed] and whether the threat to that individual poses a threat to other members of the group,” says Buchanan. Also, since the stress response prepares the body for fight or flight, perhaps the empathetic stress mobilizes the energy needed to come to the other person’s aid.

“The constant stream of devastating news with which we are confronted with in the daily media has the potential to compromise a significant range of people.”

Of course, stress can have downsides. “The stress response is brilliant for getting you through a crisis, but things get stranger when we are stressed for purely psychological reasons,” says Robert Sapolsky, a neuroscientist at Stanford University. “If you are sitting there, pulsating with frustration in a traffic jam, your body is doing the same thing as if you were running away from a lion. But in those cases, you don’t need to.” Humans, as well as some other primates, are unmatched in having the ability to generate psychosocial stress, he adds. The relative safety from predators and the high amounts of leisure time that we now enjoy means that the biological stress-coping mechanisms that were once so vital can now cause more harm than good. (For more from Sapolsky on how the mind works, see the stories he’s written for Nautilus: “Metaphors Are Us” and “On the Origin of Celebrity.”)

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As a result, stress is now a major health threat. According to the World Health Organization, stress disorders are some of the more commonly occurring of all mental disorders. Increased levels of glucose in the blood increase the risk of adult onset diabetes, and increased blood pressure leads to heart disease. Stress weakens the immune system, diminishes the chances of getting pregnant, and plays a major role in triggering and increasing the frequency of headaches, including migraines. It has also been linked to intestinal problems, gum disease, skin disorders, growth problems, and even cancer.

The presence of empathetic stress suggests that, through no fault of their own, other people’s stress could exact a cost on your health. Since the power of empathetic stress is proportional to the emotional connection between two people, this phenomenon might put caregivers and families with chronically stressed individuals at higher risk. 

In addition, given that even people watching strangers on TVs experienced empathetic stress, the negative effects could be more widespread. “The constant stream of devastating news with which we are confronted with in the daily media has the potential to compromise a significant range of people,” the authors write. They call for further research to try to circumvent the possible adverse effects. 

“The work by Engert and [her colleagues] suggests that we need to look beyond the individual and try to understand how stress can spread to children, spouses and others,” says Buchanan. “People may think they can hide their stress from loved ones or co-workers, but in many cases, they do not, and so others around them may be affected without knowing.” Some of society’s most giving members may need help themselves in coping with the load they take on.

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Simone M. Scully is a science and culture journalist based in New York City and an editorial intern at Nautilus. Follow her on Twitter at @ScullySimone.

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