Exogenous vs Endogenous

These terms refer to the origin of an actor or phenomenon – did it come from inside the body or network, or from outside?

“Endo” means “within,” so an endogenous actor is something that originated from inside some larger construct. “Exo” means “outside,” so an exogenous actor is something that originated from outside the larger construct.

Why I Looked It Up

In a book about power networks:

More recent research has shown that even emotional states can be transmitted through a network. Though distinguishing between endogenous and exogenous network effects is far from easy, the evidence of this kind of contagion is clear: “Students with studious roommates become more studious. Diners sitting next to heavy eaters eat more food.”

In looking this up, I found that the words are most often used in medicine. For example:

The main difference between exogenous and endogenous antigens is that the exogenous antigens enter the body from the outside whereas the endogenous antigens are generated inside the body.