Introduction
Movement of electrons generate electromagnetic wave; movement in a magnetic field also generates electromagnetic waves. Light itself is a form of EMF. This basic physics is as old as time.
EMF is a subset of the general term "radiation." While some "radioactive decay" events can produce EMF (such as gamma rays), other events produce energetic particles such as "neutrons," "alpha rays (positively charged)," and "beta rays (negatively charged)." The motion of these charged particles also generates EMF. This article does not address products of radioactive decay.
Human physiology has always generated electromagnetic fields, and humans have always been subjected to externally generated electromagnetic fields.
However, modern technology bathes the environment with hitherto unknown forms of EMF at relatively high powers. In some cases these forms of EMF have been used therapeutically, but overall there is reason to believe that some forms of EMF are harmful.