Increased levels of the pro-inflammatory cytokine IL-6 during illness decrease sex drive and reduce testosterone and estrogen levels.

“Well, it turns out that it can be explained by the release of what are called inflammatory cytokines, so cytokines are related to the immune system, they travel in the lymph and in the blood, and they attack invader cells like bacteria and viruses, and under conditions of illness, we make a lot of different cytokines, some of them are anti-inflammatory, but some of them are pro-inflammatory, and the best-known example of a pro-inflammatory cytokine is IL-6, and it's known that IL-6, when injected into individuals, will decrease the desire for sex and eventually will reduce levels of testosterone and estrogen independent of feeling lousy”