While we all think we know what stress is, for psychologists, stress is a useless term. This is because it is a highly subjective phenomenon that means different things to different people. The term was first used by Hans Selye, and it referred to “the non-specific response of the body to any demand for change”. He proved that stress exists by putting lab animals through various physical and emotional stimuli which resulted in the same pathological changes such as stomach ulcerations, shrinkage of lymphoid tissue and enlargement of the adrenals. He showed that when these lab animals are exposed to persistent stress, they can develop diseases like rheumatoid arthritis, kidney disease, heart attacks and stroke. At the time it was believed that diseases were caused by pathogens, but Hans proposed that stress could be the cause of these diseases in animals as well as humans.
Over time, the stress became a buzz word used by many to describe a hard day at work, an unfriendly driver or another unpleasant situation they went through. At one point scientists were so frustrated by the vague use of the word, that in an issue of British Medical Journal, one physician concluded that “stress in addition to being itself, was also the cause of itself, and the result of itself”. It was tough to translate the word into other languages and convey its true meaning, which was really strain. It was ultimately adapted into other languages and spread throughout the world.
However, to distinguish the stimulus from the response, a new word had to be created (stressor). Another problem was that stress was considered to be synonymous with distress, and even in dictionaries, it was implied that stress was negative. Although, stress can lead to increased productivity (up to a certain point). However, people need to be aware where that turning point between increased productivity and rapid downfall is. Salye also used a term called eustress, which he used to describe positive stress. Stress that can arise from a positive situation such as winning a chess match, or kissing someone for the first time and contemplating about what might happen next. Because this stress is certainly different from something you would experience having your root canal done or right before surgery.
It was a constant struggle for Salye to define stress, and he redefined it as “the rate of wear and tear on the body“. This makes sense as stress can accelerate a lot of processes that have to do with aging. Later on, Salye went to say that “everyone knows what stress is, but nobody really knows”. A great example of why stress is so difficult to define is a roller coaster. Some people are holding on for their lives, others are laughing, and some are just straight bored. Everyone perceives situations and stress differently. 
Currently, the term “stress” is defined by Merriam-Webster as “a physical, chemical, or emotional factor that causes bodily or mental tension and may be a factor in disease causation“.
Why do we experience stress?
Evolutionarily speaking, it makes sense why we experience stress. After all, if a big wolf attacked a human in the forest, stress kicked in and triggered our fight-or-flight response. It was a survival instinct. However, in modern times, with no wolves around, we still experience stress. With a deadline approaching, a big exam, or even after a breakup, we experience stress. Animals are able to control this stress response, however, we as humans have not discovered the on/off switch. That’s why, even long after the initial trigger we can experience an increased heart rate, muscles tensing and stomach turning.
Can stress kill you?
In our world, the overbearing work, responsibilities, and unexpected situations, stress can get the best of us. But what does it really mean for your health? Can stress really kill you?
In Japan, there’s a term “Karoshi” which literally translated means death from overwork. After it was discovered that many young people in seemingly great health were dying in huge quantities, and after research, Japan attributed this to what is now known as the overwork epidemic. This overload is now linked to heart attacks and strokes, and one of the causes is physical and psychological stress. 
So stress is literally killing people, but how is it possible? Cortisol is one of the main stress hormones. Its job is to direct energy where your body needs it and away from where it doesn’t. But with chronic stress exposure, your body is overwhelmed and it leads to immune system shutting down, inflammation being inhibited, white blood cells reduced and susceptibility to the disease being increased. Some studies even suggest that prolonged stress contributes to the development of certain cancers. 
When studying macaque monkeys, researchers found that those which were experiencing stress were more likely to overeat. This can lead to clogged arteries, which then prevents blood getting to the heart quickly during stress and can lead to a heart attack. This may be because of a complicated relationship between stress, social, and environmental factors.  
Your heart and blood vessels aren’t the only things at risk when it comes to stress. Your brain is also under threat. Studying mice shows us that mice exposed to stress have smaller brain cells with fewer branch extensions than those who were not. This is particularly true in areas that deal with memory and learning. That’s why those late night studies with stress combined with sleep deprivation are so highly inefficient and create difficulties in learning.  
Stress can also shorten your life as it is found to accelerate the shortening of telomeres. The rate at which you lose telomeres is linked to the length of life.  
But don’t stress about stressing out just yet. Your body also produces a hormone called oxytocin which allows blood vessels to relax and allows your heart to regenerate.
How can you reduce stress?
Boost Your Oxytocin Naturally
The hormone oxytocin mentioned earlier is a natural antidote against stress produced by your body. But how do you get more of it? Oxytocin is also known as the “cuddle hormone” because it’s produced in positive social interactions. By interacting with others, you can build resilience to stress. So when life gets tough, spend time with people you love and you may just save your life.   
The easiest way to not stress is to prevent it. It’s easier said than done, since life is no unpredictable, nonetheless, it’s safe to say that most stress can be prevented. If driving is stressful to you, consider adjusting the way you drive. Giving yourself more time to get somewhere or not leaving the last minute can prevent you from getting into unpleasant mind states. Just pace yourself, adapt yourself, and adjust your life to best suit you.
Rewire Your Brain
Just like in our roller coaster example, in life, different people respond to identical situations differently. However, that does not mean that you can’t change your response. After all, stress depends on how you perceive a situation. So train your brain to function well in high-stress situations and over time, those situations will be a walk in the park. This is why after practicing their shots thousands of times, great shooters in the NBA can nail that buzzer beater. They have trained their entire lives for that moment, visualized the situation, so when they finally got there, they were ready. Many factors go into that moment, but stress is not the major part of it.
However, what about situations such as another driver cutting you off and triggering road rage? Situations like this depend on the well-being of your mental state. Every situation can be perceived as the end of the world if you have no self-control and are short-tempered. Training your brain and setting good habits can prevent that. Here’s something that I love:
You have $86,400 in your account and someone stole $10 from you, would you be upset and throw all of the $86,390 away in hopes of getting back at the person that took your $10? Or move on and live? Right, move on and live. See, we have 86,400 seconds in every day so don’t let someone’s negative 10 seconds ruin the rest of the 86,390. Don’t sweat the small stuff, life is bigger than that.”
Preventing stress can be as easy as adjusting your attitude and how you perceive each situation. If that doesn’t help, train yourself to become more patient and positive. Meditation and yoga can help. Next time you get in that roller coaster situation, you’ll be the one smiling and enjoying the ride, or at the very least, moving forward with your life.
Once something has already occurred, it’s too late to prevent it. Luckily, certain foods can help your body in distress and help calm and balance itself. They can boost your bodies natural abilities in fighting stress and promoting a quicker recovery.
Berries – Blueberries, for example, can boost a type of white blood cells which plays a key role in your immune system, critical for countering stress.
Whole grains – Carbohydrates to boost serotonin production 
Fish – Omega 3 Fatty Acids (salmon, mackerel, tuna, herring, trout, halibut, sardines) are linked to reduction in anxiety and inflammation. Walnuts, avocados, pumpkin seeds, edamame for those who don’t eat fish.
Beans – Rich in magnesium. Several studies linked magnesium supplements to the reduction of mania and mood cycling.
Apples, oranges, bananas – These foods are high in Vitamin C, which several studies have credited to being able to reduce both physical and psychological stress.
Herbal tea – Used for centuries for reducing anxiety and helping with insomnia. Try out chamomile and spearmint teas for a sedative effect.
Chocolate – May help regulate your stress hormones. A study found that eating an ounce of dark chocolate per day was enough to reduce the stress levels of participants.
Avoid alcohol and caffeine.
While caffeine may be part of your daily ritual, it can cause more anxiety and put you in a jittery state, which is not exactly what you need in times of stress. Alcohol can sometimes take the edge off during stress, but as it wears down it can make you feel even worse. Not to mention that overconsumption can lead to a variety of other health problems.