Despite the headline, this is not an “R Rated” article, but rather a discussion of hormonal molecular physiology. Cortisol and testosterone might seem to be totally different compounds but they are actually very closely related. Cortisol’s formula is C₂₁H₃₀O₅ while that of testosterone is C₁₉H₂₈O₂, plus they share the identical five hydrocarbon ring structure. Another similarity is that they both can reduce immune function. This is one reason males are more prone to illness than females.  

Our adrenal glands primarily produce aldosterone, cortisol and adrenalin, but also small amounts of the sex hormones estrogen, progesterone and testosterone.  

Our gonads produce estrogen, progesterone and testosterone in different proportions based on our sex. It all comes down to slight modifications of the hydrocarbon ring structure that they all have in common.  

It has been known for quite some time that elevated cortisol, either exogenous (from our adrenal glands) or exogenous (from pharmaceuticals), impairs immune function.  

The higher the elevation the greater the immune suppression. What has more recently been learned is that testosterone has a similar effect even at normal levels but more so at higher levels.  

The main reason for elevation of endogenous cortisol is stress, both acute and chronic. This is one reason people frequently get sick on a trip or a vacation. Our adrenal glands make adaptive changes for even the pleasant disruptions of locale, diet, activity, sleep and wake times associated with travel. The attendant elevation of cortisol makes illness more likely. 

The immune dysregulation from cortisol and testosterone occurs in both the innate and adaptive arms of over immune function. Over innate immune system, which is the more primitive system and shared with less complex organisms, works to a large degree by pattern recognition receptors. These receptors are suppressed by cortisol and testosterone. The adaptive arm of over immune function relies on its ability to proliferate the formation/function of both T-cells and B-cells. This ability is suppressed by cortisol and testosterone. Moreover, they also promote lymphocyte apoptosis (cellular suicide).