Stress is how the body reacts to a stressor, real or imagined, a stimulus that causes stress. Acute stressors affect an organism in the short term; chronic stressors over the longer term. Selye researched the effects of stress on rats and other animals by exposing them to unpleasant or harmful stimuli. He found that all animals display a similar sequence of reactions, manifesting in three distinct stages. He labeled this universal response to stressors the general adaptation syndrome or GAS. Alarm is the first stage. When the threat or stressor is identified ...