The natural responses to stimuli in the environment, particularly stressors, trigger hormonal and physiological changes that activate the sympathetic nervous system and therefore disrupt homeostasis, the stable equilibrium conditions that regulate the body. The stress or fight-or-flight response is the part of the body's defense mechanism, and has as its purpose the redirecting of physical energy towards evading harmful or potentially deadly situations. In the process, hormones are released, notably cortisol and epinephrine, triggering various physiological changes that provide additional energy to the brain and muscles
In the primitive environment most flight-or-fight responses were induced by life threatening situations, and were followed by intense physical activity, providing relief and the quick return to homeostasis. Modern day psychological or perceived stressors are much more frequent and most often are not followed by intense physical activity, leading to prolonged exposure to an activated sympathetic nervous system and stress-related hormones, including cortisol and epinephrine. While much research remains to be conducted on the matter, such chronic exposure to stress responses seems to suppress the immune system, opening the living system to attacks from viruses, bacteria and tumors, and has also been associated with various other negative health effects and negative effects on bodily functions, including:                vulnerability to common infectious diseases such as colds and flu;        digestive problems such as irritable bowel syndrome and ulcers;        increased vulnerability to anxiety and depression;        cortisol contributes to infertility and increased risks of miscarriage;        premature aging;        slow wound healing;        impairment of developmental growth in children;        cortisol has been linked to impairment of learning and memory loss; and        accumulation of visceral fat, which is itself linked higher risks of heart attack and stroke.        
With so many adverse health effects linked to stress, there is a need to properly diagnose or bring awareness to situations which cause stress or disrupt homeostasis, so that they can be better avoided or so that stress coping mechanisms, such as physical activity, thinking pleasant thoughts or listening to music, can be deployed. There is also a need to record the events causing stress and the stress responses associated with them so that events causing stress, and which events caused more significant amounts of stress, can be determined, so as to aid in avoidance or treatment subsequently.
Any means for diagnosing stress responses should be light and easily portable, so that the user can use it ubiquitously, and in the user's normal environment—rather than only in a medical setting.