In general, the two main ingredients needed to produce diseases are an invading foreign substance and a lowered resistance.
The invader could be anything from a virus, fungus, parasite or bacteria to an abnormal growth in tissue, resulting in a tumor or cancer.
The lower the resistance, or the slower the response to the invader, the more likely that the disease will establish itself and overwhelm homeostatic mechanisms.
Any type of physical, emotional, or psychosocial stress can have a devastating effect on the immune response and make us more susceptible to disease.
This is because the hypothalamus of the brain sends defense signals to the endocrine system, which then releases a multitude of hormones that get us ready for emergency situations but which mobilize or severely depress immunity.
So here, just as in other physiological processes, the neuro-endocrine-immune system is at the very heart of the stress response, which is really a series of chemical reactions that wreak havoc on normal body functions.
The figure above illustrates the various reactions that occur as a result of stress.
Called the “disease of the twentieth century,” stress, according to experts, will cause more health problems and trigger more disease in the twenty-first century than ever before. No single factor has had or will have such an impact on so many individuals.