Stress and its effects were discovered in a rather unappetizing way (if you’re prone to anxiety, read no further). In 1936, an endocrinologist (a scientist studying hormone effects) by the name of Hans Selye subjected his lab rats to various stressors that make next week’s test look tame. He then ended their misery and studied their organs for measurable evidence of responses to the stress.

Selye discovered that the physical effect of any stress (whether it was excessive exercise or exposure to cold) was the same: alteration to the animals’ internal organs, especially the adrenal glands.

Human reactions to stress seem to vary depending on personality, stress level, and stress cause, but the internal response is universal. Stressors initiate the release of the hormone epinephrine (also known as adrenaline) from the adrenal glands (located above the kidneys). The neurotransmitter triggers what is commonly called the “fight-or-flight” response. The presence of epinephrine in the human endocrine system causes this psychological and physiological impulse to either fight or escape the cause of the stress.

This internal response to stress is often beneficial — it can temporarily increase strength and speed and protect against anaphylactic shock (which is why an “EpiPen,” which contains a drug form of epinephrine, is the initial treatment for allergic reactions). Epinephrine increases heart rate, opens airways and diverts blood to the muscles where it is most needed to fight or flee.

However, prolonged or frequent stressors may have negative effects on human health. When the stressor is something such as an exam or essay, which cannot be fought or fled in the conventional sense, the involuntary stress response is far from advantageous.

Stress, as almost any college student can attest to, wears the body down. The human body’s ingrained response actually diminishes memory and thinking ability, because it diverts blood from the brain to the large muscles required for either fighting or fleeing. Chronic stress can impact digestion, because the intestines and other internal organs are temporarily shut down to enable energy use where it would be most advantageous in a fight.

According to Betty Burrows of “How Stuff Works,” prolonged or incessant stress also decreases immunity, thereby increasing vulnerability to infections.

“The problem in modern times,” Burrows writes, “is that our body’s stress response is regularly triggered even though our lives are not in danger.”

Odd though it seems, stressing over that test or assignment may do more long-term damage to your health than the test or assignment itself can. These days, stress is more likely to kill us than the stressors are.