What Causes Stress?

Learn how the body reacts to stress.

Regardless of the cause, stress sets in motion certain automatic changes in the body that are designed to give it a quick burst of energy. The pattern of changes has been called the "fight-or-flight" response because it most likely evolved from our prehistoric ancestors, who faced daily dangers in their search for food and shelter and had to either flee or do battle. Of course, we no longer face such dangers, but our bodies continue to react as if we did. So instead of responding to a saber-tooth tiger lurking behind a tree, the body reacts to petty annoyances like getting caught in traffic, being reprimanded by a supervisor, or worrying about bills. Regardless of the type of stress, the body goes through the following changes:

• The adrenal glands release adrenaline and other stress hormones that prime certain organs to go into action.
• The breathing becomes faster and more shallow to allow the body to take in more oxygen.
• The liver releases more glucose (blood sugar) to provide extra energy.
• The heart beats faster and blood pressure rises to increase the distribution of oxygen and nutrients throughout the body.
• Blood flow to the brain and muscles is increased and, at the same time, reduced to digestive organs.

Sweating increases to allow the body to burn more calories without a rise in body temperature. (In theory, sweating also makes the skin slippery and more difficult for a predator to grab.)

After the stressor disappears, the body returns to its normal state (homeostasis). If, however, stress is chronic -- as it is for many people -- the body stays on high alert. The many damaging consequences include a rise in cholesterol levels, high blood pressure, damaged blood vessels, decreased mental skills, and a weakened immune system.