Stress is a state of mental tension or emotional strain due to adverse or demanding circumstances, events, and situations.Stress is hard to measure and someone may be suffering from it while showing no external signs.

Stress defined

The American Psychological Association (APA) says that the most common causes of stress (in the US) are finance, work, and family-related and that they affect more of the younger generations.

Causes of stress

There is a constant need to be hyper-connected in today's modern workplaces, leading to a constant feeling of anxiety. Social media is bombarding everyone with unattainable, unrealistic goals. There are rising cases of high blood pressure, headaches, and insomnia, all related to stress. Constant stress can lead to heart disease, diabetes, mental disorders and depression.

Constant stress

A limited amount of stress can actually be beneficial. Situations and circumstances like a deadline, or a sports competition can boost the body in constructive and positive ways.The body also recognizes 'good stress' which is positive in its workings on the body, during moderate challenges.

Moderate stress is good

In less extreme situations, the body and brain produce adrenaline, and the heart provides more blood, the brain is sharper and the body releases stress hormones, which can be beneficial in coping up and handling those situations.

Stress can make us stronger

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<img src="https://www.economist.com/sites/default/files/images/print-edition/20160723_IRD001_1.jpg">FOR centuries physicists have used the word stress to describe force applied to materials. It was not until the 1930s that Hans Selye, a Hungarian-born endocrinologist, began using it of live beings. Selye injected rats with cow hormones, exposed them to extreme temperatures and partially severed their spinal cords to prove that all these sorts of maltreatment affected the rodents in the same ways: they lost muscle tone, developed stomach ulcers and suffered immune-system failure. He used the word for both the abuse of the rats and the health effects. Later on, it started to be used for psychological suffering as well.
Today, the Oxford English Dictionary defines stress as "a state of mental or emotional strain or tension resulting from adverse or demanding circumstances". The causes vary enormously: one person may be stressed by exams but happily swim with Great White sharks. Another may have to take sedatives before flying, but adore speaking to a crowd. This makes stress hard to measure. Proxies, such as the Negative Experience Index produced by Gallup, a pollster, suggest the world is growing more pessimistic, which may indicate increasing stress levels. Other surveys confirm what is perhaps obvious: stress is universal. 
The American Psychological Association (APA) suggests that, at least in America, the most common causes are to do with money, work and family. Women report being more stressed than men and are twice as likely to be diagnosed with anxiety disorders. Studies on rats indicate that sex hormones such as oestrogen and progesterone may play a part; so may the double burden of family and work. Men may also be more likely to conceal their distress. Black and Hispanic Americans, as well as poor people and parents, also report higher levels of stress. In 2015 half of Americans starting university reported being stressed most or all of the time.
Young people have long reported more stress than old people, says Mary McNaughton-Cassill of the University of Texas at San Antonio. But she believes today's youth are more overwhelmed than ever before. Globalisation means rapid change in the workplace, and firms increasingly expect employees to be constantly connected. The mass media flood us with bad news while creating unattainable aspirations, she adds: "you have to look like a movie star, stay informed about politics, take care of the kids and hold down a job." Social media, which may lower stress when used to strengthen connections with friends, have been associated with higher stress when they deliver news of friends' travails, such as divorces and accidents.
Many studies have shown that stress has similar effects on humans as on Selye's rats. It has been linked to high blood pressure, headaches, stomach upset and insomnia. According to the APA, chronic stress can "ravage" the immune system and increase unhealthy behaviours, such as drinking and smoking, that raise the risks of diabetes and cardiovascular diseases. A recent study by Bruce McEwen, a neuroscientist at Rockefeller University, showed that exposing rats to stress for just three weeks changed their brain architecture. Forcing his rats to swim, among other unpleasant tasks, shrank the dendrites in their amygdalae, the parts of the brain that control emotional responses, decision-making and memory. Though reversible, such changes in humans increase the risk of anxiety disorders and depression.
<h2>Snapping point</h2>
Late in his career Selye came to distinguish between "eustress", or the good stress caused by positive experiences, such as falling in love, and distress, the bad sort. Other scientists extended the original physics metaphor: just as many materials can withstand stress until a certain point, it was thought that humans could cope with stress if it did not become too severe. Indeed, the idea took hold that moderate stress might be a good thing. In 1979 Peter Nixon, a consultant at Charing Cross Hospital in London, described a "human function curve": a moderate amount of stress, such as a deadline or race, was now understood as not just harmless, but beneficial. But above a certain threshold humans, like metal bars, would break.
Now a new body of research is challenging that notion. Some scientists posit that what matters is not just the level of stress, or even its type, but how it is thought about. The same stress, perceived differently, can trigger different physical responses, with differing consequences in turn for both performance and health.
Recognising that stress can be beneficial seems to help in two main ways. People who have a more positive view of stress are more likely to behave in a constructive way: a study by Alia Crum of Stanford University's Mind and Body Lab and others found that students who believed stress enhances performance were more likely to ask for detailed feedback after an uncomfortable public-speaking exercise. And seeing stressors as challenges rather than threats invites physiological responses that improve thinking and cause less physical wear and tear.
Humans can respond to stress in several different ways. The best-known is the "fight or flight" response, which evolved as a response to sudden danger. The heart rate increases; the veins constrict to limit the bleeding that might follow a brawl and send more blood to the muscles; and the brain focuses on the big picture, with details blurred.
In less extreme situations, the body and brain should react somewhat differently. When people perceive they are being challenged rather than threatened, the heart still beats faster and adrenalin still surges, but the brain is sharper and the body releases a different mix of stress hormones, which aid in recovery and learning. The blood vessels remain more open and the immune system reacts differently, too. Sometimes, though, the wrong response is triggered, and people sitting exams, giving a speech or pitching a business plan react as if to a sudden threat, with negative consequences for both their performance and their long-term health.
Ms Crum believes that attitudes and beliefs shape the physical response to stress. In 2013 she subjected student volunteers to fake job interviews. Beforehand, they were shown one of two videos. The first extolled the way stress can improve performance and forge social connections; the second emphasised its dangers. In the fake interviews, the participants were subjected to biting criticism. When Ms Crum took saliva samples at the end of the study, she found that those who watched the upbeat video had released more DHEA, a hormone associated with brain growth.
In an earlier study Ms Crum and Shawn Achor, the author of "The Happiness Advantage", visited UBS, an investment bank, at the height of the financial crisis in 2008. They split around 400 bankers into three groups. The first watched a video that reinforced notions of stress as toxic, the second watched one highlighting that stress could enhance performance and the third watched no clip at all. A week later the second group reported greater focus, higher engagement and fewer health problems than before; the other two groups reported no changes.
Other scientists have shown that recognising the benefits of stress can cause measurable improvements in performance. In one experiment Jeremy Jamieson, a psychology professor at the University of Rochester, gathered college students preparing for the Graduate Record Examination (GRE), an entrance test for postgraduate courses. He collected saliva from each of the students to measure their baseline stress response and divided them into two groups. One group was told that stress during practice exams was natural and can boost performance; the other got no such pep talk. The students who received the mindset intervention went on to score higher on a GRE practice test than those who did not. When Mr Jamieson collected their saliva after the exam, it suggested his intervention had not soothed their nerves: they were at least as stressed as those in the control group. A few months later the students reported their scores on the real GRE exam: those who had been taught to see stress as positive still scored better.
"Google images of stress and you'll see a guy with his head on fire. We've internalised that idea," says Mr Achor. He instead compares stress to going to the gym. You only get stronger if you push yourself beyond what feels easy, but afterwards you need to recover. The analogy suggests that stress at work may be performance-enhancing, but should be followed by rest, whether that means not checking e-mails on weekends, taking more holiday or going for a stroll in the middle of the day.
<h2>The well-tempered mind</h2>
Kelly McGonigal, a psychologist at Stanford University and the author of "The Upside of Stress", helps people rethink stress by telling them that it is what we feel when something we care about is at stake. She asks them to make two lists: of things that stress them; and of things that matter to them. "People realise that if they eliminated all stress their lives would not have much meaning," she says. "We need to give up the fantasy that you can have everything you want without stress."
By changing how their bodies process stress and how they behave, such reframing may help people live healthier lives. In 2012 a group of scientists in America looked back at the 1998 National Health Interview Survey, which included questions about how much stress the 30,000 participants had experienced in the previous year, and whether they believed stress harmed their health. Next, they pored over mortality records to find out which respondents had died. They found that those who both reported high stress and believed it was harming their health had a 43% higher risk of premature death. Those who reported high stress but did not believe it was hurting them were less likely to die early than those who reported little stress.
The study shows correlation, not causation. But since much stress is unavoidable, working out how to harness it may be wiser than fruitless attempts to banish it.
This article appeared in the International section of the print edition under the headline "What makes us stronger"
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FOR centuries physicists have used the word stress to describe force applied to materials. It was not until the 1930s that Hans Selye, a Hungarian-born endocrinologist, began using it of live beings.

What makes us stronger

Stress defined

Causes of stress

Constant stress

Moderate stress is good

Stress can make us stronger

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