"Cortisol is used in virtually every system in the body, a hormone that literally integrates the body and the mind by altering the configuration of the brain. Cortisol interferes with the immune system, changes the sensitivity of the ears, nose and eyes, and alters various bodily functions. When you have a lot of cortisol coursing through your veins, you are--by definition--under stress. Cortisol and stress are virtually synonymous.
In white blood cells cortisol is almost certainly involved in switching on a gene called TCF, also on chromosone IO, thus enabling TCF to make its own protein, whose job is to suppress the expression of another protein called interleukin 2, and interlukin 2 is a chemical that puts whte blood cells on alert to be especially vigilant for germs. So, cortisol supresses the immune alertness of white blood cells and makes you more susceptible to disease."
--Genome by Matt Ridley
It seems like one of the hundreds of times I bemoaned my susceptibility to illness, someone might have told me that my stress-monkey nature that is to blame.