is the body's emergency

response to real or imagined danger. A stress reaction prepares the body for a burst of action to fight or flee a threat. The heart races, hands get cold and sweaty, muscles tense, and the stomach feels jittery. Stress that lasts a long time can exhaust the body and cause a frazzled mental state of feeling worried and overwhelmed. Any event, thought, or situation that causes stress is called a stressor.

Stress aids survival, especially in cases when extraordinary effort can overcome real physical dangers. Stress was particularly useful for prehistoric people when life was filled with such stressors as defending shelter and hunting large animals. As civilization developed, life for most people became less physically dangerous. But as society became more complex, mental and emotional challenges increased and became common stressors.

Stress is not always useful as a response to mental and emotional stressors. A mild level of stress can provide a sense of excitement and help people perform at their peak. But severe stress can fill people with worry and prevent effective behavior. Stress that lasts a long time can weaken health and interfere with happiness.

Causes of stress. Modern life exposes people to many stressors. Some physical stressors remain, including natural disasters, illnesses, and noise. Certain life experiences, such as the death of a loved one, are major stressors. Day-to-day problems, such as burning toast, taking tests, or feeling rushed, may also be stressful.

People need not experience events directly to feel stress. Television, newspapers, and other means of mass communication flood people with information about upsetting occurrences throughout the world. People can also imagine future misfortunes and regret past failures.

Many experts consider modern life particularly stressful for children and families. Divorce and separation bring stress into the lives of many people. As a result of family disruptions or births outside marriage, increasing numbers of children grow up in single-parent homes. Many parents without partners work exceptionally hard to meet their families' emotional and financial needs and to fulfill their household duties.

How stress affects the body. Canadian scientist Hans Selye pioneered studies of stress in the 1930's. He used the term general adaptation syndrome to describe the body's reaction to stressors. The first part of the general adaptation response, called an alarm reaction, occurs when a person or other animal first senses danger.

An alarm reaction begins in the brain when a frightening experience activates an area called the hypothalamus. The hypothalamus then sends nerve signals to the adrenal glands, which sit above the kidneys. These nerve signals stimulate the medulla (inner core) of the adrenals to release chemical messengers called hormones. The most important of these hormones is epinephrine, which is also called adrenalin. Epinephrine raises heart rate, breathing rate, blood pressure, and the amount of sugar in the blood. These effects increase alertness and deliver more blood, oxygen, and food to active muscles.

If danger persists, a stage called resistance follows the alarm reaction. During resistance, the body attempts to return to a state of balance. Breathing and heart rate decrease to normal levels. But the hypothalamus sends a hormone signal to a nearby gland called the pituitary. The pituitary gland then releases adrenocorticotropic hormone, also called ACTH. ACTH travels to the cortex (outer layer) of the adrenal glands. The adrenal cortex responds by releasing hormones called glucocorticoids. These hormones keep blood sugar high to provide extra energy.

If stress continues at high levels, the body enters the final stage of the general adaptation syndrome-that is, exhaustion. In exhaustion, energy reserves are used up, leading to extreme fatigue and inability to resist new stressors. Long-term stress can lead to serious illness.

Stress-related illnesses. Many doctors estimate that stress is involved in more than half of all illnesses. It may cause or prolong an illness or increase its severity. Hormones released during a stress reaction affect organs throughout the body. Heredity, learning, and injuries all play a role in determining where or when a stress-related illness may occur in a particular individual.

Stress hormones that act on the heart, blood vessels, and lungs may contribute to heart disease, high blood pressure, and asthma. Prolonged elevation of blood sugar can influence development of diabetes. Diseases of the stomach and intestines are often linked to stress because blood leaves these organs and moves to muscles used in running and fighting. Extended exposure to mental and emotional stressors can lead to difficulties in eating, sleeping, and making decisions. People may also feel angry, depressed, and overwhelmed.

Glucocorticoid hormones can interfere with the body's immune (disease-fighting) system. During prolonged or repeated stress, people may find themselves more likely to get colds, flu, and many other diseases.

Managing stress. Stress is an individual reaction to something that a particular person finds alarming. Understanding how they react to stress can enable people to control or reduce some of their stress reactions. One important way people can manage stress is to learn to question whether experiences that they fear are truly dangerous. By asking questions and sharing information about the world, people can avoid jumping to conclusions and exaggerating the importance of events. For example, someone who finds taking tests extremely stressful might ask such questions as (1) Is there a friend who could help me study? (2) How much does the test really count? (3) Can I talk with the teacher if I feel that my performance does not reflect my knowledge of the subject?

Relaxation techniques are another useful means of managing stress. These techniques include breathing deeply and slowly, tensing and then relaxing each muscle in the body, and imagining a calm, peaceful place. More formal relaxation techniques include meditation, hypnosis, taped relaxation programs, and biofeedback training.