This definition is just one of many that are possible. What constitutes "good" health, in particular, can vary widely. The rather fragile individual who stays "well" within the ordinary environment of his or her existence may succumb to a heart attack from heavy shoveling after a snowstorm; or a sea-level dweller may move to a new home in the mountains, where the atmosphere has a lower content of oxygen, and suffer from shortness of breath and anemia until his or her red blood cell count adjusts itself to the altitude. Thus, even by this definition, the conception of good health must involve some allowance for change in the environment

Bad health can be defined as the presence of disease, good health as its absence—particularly the absence of continuing disease, because the person afflicted with a sudden attack of seasickness, for example, may not be thought of as having lost good health as a result of such a mishap actually, there is a wide variable area between health and disease. Only a few examples are necessary to illustrate the point: (1) It is physiologically normal for an individual to have a high blood sugar content 15 to 20 minutes after eating a meal. If, however, the sugar content remains elevated two hours later, this condition is abnormal and may be indicative of disease. (2) A "healthy" individual may have developed an allergy, perhaps during early childhood, to a single specific substance. If the person never again comes in contact with the antigen that causes the allergy, all other factors remaining normal, he or she will remain in that state of health. However, should the individual come in contact with that allergen again, even 20 or 30 years later, he or she may suffer anything from a mild allergic reaction—a simple rash—to severe anaphylactic shock, coma, or even death, depending upon the circumstances. Thus it can be seen that, unlike disease, which is frequently recognizable, tangible, and rather easily defined, health is a somewhat nebulous condition and somewhat difficult to define.