You can control some of the stresses on your body; for example, you can determine how much you eat and how much you exercise. These stresses fall into the physiological stressor category. Then, there are environmental stressors, such as environmental pollution and substance addiction.

• Environmental stressors. These are things in your immediate environment that put stress on your physical body. These include air pollution, polluted drinking water, noise pollution, artificial lighting, bad ventilation, or the presence of allergens in the field of ragweed outside your bedroom window or in the dander of the cat who likes to sleep on your pillow.

• Physiological stressors. These are the stressors within your own body that cause stress. For example, hormonal changes that occur during pregnancy or menopause put direct physiological stress on your system, as does premenstrual syndrome (PMS). Hormonal changes may also cause indirect stress because of the emotional changes they cause.

  Also, bad health habits such as smoking, drinking too much, eating junk food, or being sedentary put physiological stress on your body. So does illness, whether it's the common cold or something more serious like heart disease or cancer. Injury also puts stress on your body — a broken leg, a sprained wrist, and a slipped disk are all stressful.

Just as potent but less direct are stressors that impact your body by way of your mind. For example, getting caught in heavy traffic may stress your body directly because of the air pollution it creates, but it may also stress your body indirectly because you get so worked up and irritated sitting in your car in the middle of a traffic jam that your blood pressure rises, your muscles tense, and your heart beats faster. If you were to interpret the traffic jam differently — say, as an opportunity to relax and listen to your favorite CD before getting to work — your body might not experience any stress at all. Again, attitude plays a major role.

Pain is another, trickier example of indirect stress. If you have a terrible headache, your body may not experience direct physiological stress, but your emotional reaction to the pain might cause your body significant stress.

People tend to be fearful of pain, but pain is an important way to let us know something is wrong. Pain can signal injury or disease. However, sometimes we already know what's wrong. We get migraines, or have arthritis, or experience menstrual cramps, or a bad knee acts up when the weather changes. This kind of “familiar” pain isn't useful in terms of alerting us to something that needs immediate medical attention.

But because we know we are in some form of pain, we still tend to get tense. “Oh no, not another migraine! No, not today!” Our emotional reaction doesn't cause the pain, but it does cause the physiological stress associated with the pain. Pain in itself isn't stressful. Our reaction to pain is what causes stress. So, learning stress management techniques may not stop pain, but it can stop the physiological stress associated with pain.

When your body is experiencing this stress response, whether caused by direct or indirect physiological stressors, it undergoes some very specific changes. Around the beginning of the twentieth century, physiologist Walter B. Cannon coined the phrase “fight or flight” to describe the biochemical changes stress invokes in the body, preparing it to flee or confront danger more safely and effectively.

These are the changes that happen in your body every time you feel stressed, even if running away or fighting aren't relevant or wouldn't help you (for example, if you're about to give a speech, take a test, or confront your mother-in-law about her constant unsolicited advice, neither fight nor flight are very helpful responses).

Here's what happens inside your body when you feel stress:

• Your cerebral cortex sends an alarm message to your hypothalamus, the part of your brain that releases the chemicals that create the stress response. Anything your brain perceives as stress will cause this effect, whether or not you are in any real danger.

• Your hypothalamus releases chemicals that stimulate your sympathetic nervous system to prepare for danger.

• Your nervous system reacts by raising your heart rate, respiration rate, and blood pressure. Everything gets turned “up.”

• Your muscles tense, preparing for action. Blood moves away from the extremities and your digestive system, into your muscles and brain. Blood sugars are mobilized to travel to where they will be needed most.

• Your senses get sharper. You can hear better, see better, smell better, taste better. Even your sense of touch becomes more sensitive.

That sounds like a way to get things done, doesn't it? Imagine the high-powered executive, stunning clients with an on-target presentation and sharp, clever answers to every question. Imagine the basketball player at the championship game, making every shot. Imagine the student acing that final exam, every answer coming immediately to mind, the perfect words pouring from the pen for that A+ essay. Imagine yourself at the next office party, clever and funny, attracting crowds that hang on your every word. Stress can be great! No wonder it's addictive.

But the downside is that stress, while beneficial in moderate amounts, is harmful in excessive amounts, as are most things. More specifically, stress can cause problems in different systems all over your body. Some problems are immediate, like digestive trouble or a racing heartbeat.

Other problems are more likely to occur the longer you are under stress. Some of stress's less desirable symptoms, directly related to the increase in adrenaline in the body, include the following:

• Sweating

• Cold extremities

• Nausea, vomiting, diarrhea

• Muscle tension

• Dry mouth

• Confusion

• Nervousness, anxiety

• Irritability, impatience

• Frustration

• Panic

• Hostility, aggression

Long-term effects of stress can be even harder to correct, and include such things as depression, loss or increase of appetite resulting in undesirable weight changes, frequent minor illnesses, increased aches and pains, sexual problems, fatigue, loss of interest in social activities, increased addictive behavior, chronic headaches, acne, chronic backaches, chronic stomachaches, and worsened symptoms associated with medical conditions such as asthma and arthritis.