It is as if I have in front of me three dolls: one made of steel, one made of celluloid and another of glass. I choose to hit these three dolls with a hammer using equal strength. Why is it that the steel doll will emit a beautiful musical sound? Why is it the celluloid doll will simply scar and the glass doll will shatter?

This is a metaphor for resistance and susceptibility in health and disease. The inescapable fact is that some people seem to be made of steel. They never get sick. Other folks appear to be like glass, they are forever having problems (e.g. they have more broken bones, catch colds frequently, have more pimples and blemishes, etc). Of the terms for these kinds of people, some are more descriptive than others. Some are very discreet and sophisticated, such as odds ratios and/or risk factors. Others are very simple like pluses and minuses. Among the many labels is the recognition that two forces are operating in concert. One may be viewed as the resistance factor (such as taking vitamins, hormones, eating the right food, drinking good water and breathing good air) and may be defined by those agents which invite health. In contrast, there are those elements which may be viewed collectively as the susceptibility factor which promote sickness (i.e. lead, alcohol, pesticides, tobacco, fast foods, sugar). In other words, one can establish two forces, positive and negative, in the genesis of health and sickness.