Let's start with a medical definition of stress: A physiologic reaction by an organism to an uncomfortable or unfamiliar physical or psychological stimulus. Biological changes result from stimulation of the sympathetic nervous system, including a heightened state of alertness, anxiety, increased heart rate, and sweating.
A simpler definition of stress (psychological stress), is that it's a type of strain that affects a person mentally, physically, and emotionally. The physical reactions to stress are natural defense mechanisms intended to deal with the threat of predators and aggressors. It's your body's "fight-or-flight" adrenaline response. Your body instantly shifts into high gear to deal with the emergency.
Today there are also many psychological "threats" to contend with. For example: Moving, divorce, troubles or challenges at work, exams at school, making ends meet, taking care of an ill parent or child. The less control you have over any of these events and the more uncertainty they create, the more likely you are to feel stressed.
In addition, these modern psychological threats are often prolonged. In other words, they're not over in a few minutes like a typical physical threat is. Your fight-or-flight response works overtime. While this response is good for a short-term crisis, it can be very harmful to your body when the reaction lasts longer.
The definition of stress extends to the "three types" of stress.
Acute Stress: This is the most common and it comes from events of the recent past or those anticipated in the near future. These are primarily the daily events of life: The fender bender. Missing the commuter train. A big mistake at work. Losing cable TV during the Super Bowl. And so on.
A form of acute stress is "eustress" which can be defined as a form of positive stress. In some situations you benefit from stress because it gives you your competitive edge in sports, giving a speech, job interview, or acting. Eustress provides you with focus to help you think quickly and clearly.
Eustress also keeps you vital and excited about life. Examples include the excitement of a fast challenging run down the ski slope, a roller-coaster ride, or a scary movie. Nonetheless, too much eustress can still tax your body. So be sure to have some "down time" to keep a healthy balance in your life.
Episodic Acute Stress: Basically this applies to people who experience acute stress frequently, almost on a non-stop basis. It includes people whose lives are a study in chaos and crisis. Another group of people are the "Type A" personalities. Their driving personality seems to create frequent episodes of acute stress. Then there are the endless worriers. They see disaster around every corner. If anything can go wrong it does.
Chronic Stress: It grinds people down day after day and year after year. It literally destroys bodies, minds and lives. Chronic stress can occur when a person sees no way out of a miserable situation. From being trapped in an unhappy marriage or in a job they despise. It can also be the stress of poverty or dysfunctional families.
The danger is that often people get used to it and may even forget it's there. But your body doesn't and it is paying a very high price. Chronic stress kills through suicide, violence, heart attack, stroke, and perhaps even cancer.
A complete definition of stress requires mentioning "post-traumatic stress disorder (PTSD)." PTSD is a debilitating condition that may develop after a terrifying event. War veterans first brought it into the limelight but anyone can experience it.
Examples of terrifying or traumatic events are: child abuse and domestic abuse; violent attacks, such as rape, mugging, or torture; threats of violence or verbal abuse, such as bullying; disasters, both natural and human-caused; being kidnapped or held captive; accidents; and military combat.
Regardless of the type of stress, no two people react in exactly the same way. And some people are less resistant to stress than others. This does NOT mean they're weak. Numerous recent studies, including one by the National Institute of Mental Health (NIMH), are revealing how a naturally occurring mechanism in the brain promotes resilience to psychological stress. And one day it may even be possible to increase stress-resistance in people faced with situations that might otherwise result in post-traumatic stress disorder, for example.
Having a clear understanding of the definition of stress allows you to manage and cope with it effectively. Remember, stress is natural and even beneficial at times. However, too much over extended periods of time will have serious negative impacts on your physical and mental health.