Influence of natural factors on humans or human migration into extreme conditions alters relationships between population and environment, therefore functional resources are mobilized. This alteration sometimes induces genotypic and phenotypic inadequacy to new, more strict requirements of natural and occupational factors. That is because evolution develops and genetically fixes in most people various mechanisms providing and supporting biologic balance. Requirements set in favorable environmental conditions for homeostatic systems including immune one are adequate to genotype of most individuals. When those mechanisms are not fixed and/or environmental conditions appear unfavorable the changes occur that could transform into disease.