Stress is your body's natural response to a demand or threat. It affects both the mind and the body and can be caused by "stressors" such as your environment, social situations, or an illness.
When you sense danger — real or imagined — a small region in the base of the brain reacts by making the body produce a hormone called epinephrine, or adrenaline, into your bloodstream. This starts a domino effect that can cause your heart to beat faster and your pulse and breath to quicken as your body gets ready to respond. This automatic process is known as a "stress" or "fight-or-flight response."
Over time, repeated activation of the stress response takes a toll on the body. Research suggests that chronic stress contributes to high blood pressure, promotes the formation of artery-clogging deposits, and causes brain changes that may contribute to anxiety, depression, and addiction.2