What we think and feel, and how long we think it or feel it, determines our health. The science is strong, and yet so often stress is considered an amorphous gray area, something we can’t put our finger on or measure, and so it gets dismissed as not being “real.” The chemicals your body produces when you are under stress turn on or off of genes that change everything from how much fat you store, to how well your immune system works, to how fast you age, to whether or not you will develop cancer.

Key Takeaways:

• The term “stress” originates not in our minds or bodies, but from physics. It is the internal forces generated in an object in response to an external load.
• Subjectively and physiologically, it is a movement of the mind away from relaxation and the body away from homeostasis, to respond to the challenges presented by the environment.
• Stress is best measured where our brains and bodies meet, in the Autonomic Nervous System (ANS).

"To deal with the stressor, the brain orchestrates the sympathetic branch of the ANS and neuroendocrine responses, which in conjunction dramatically alter bodily physiology, such as blood pressure, vascular tone, and cardiorespiratory dynamics."

http://www.news-medical.net/news/20161116/How-toxic-is-your-stress.aspx