, you glow in the dark!
Potassium-40 (40K) is the primary source of radiation from the human body for two reasons. First, the 40K concentration in the body is fairly high (about 2 pCi per gram of soft tissue). As a ballpark estimate, there are 200,000 disintegrations of 40K per minute in a typical human. Second, 40K emits gamma rays in a little over 10% of its decays and most of these gamma rays escape the body. In other words, the body emits close to 20,000 gamma rays per minute from 40K. The vast majority of the beta particles that 40K emits do not escape the body. There are many other radionuclides in the human body but these are either present at lower levels than 40K (for example, 238U, 226Ra, 210Pb, 210Bi, 210Po, etc.) and/or they do not emit gamma rays (for example, 3H and 14C). Radon (and its decay products) is not a significant source of radiation because it is present at very low levels in the body. There is one other (very minor) mechanism by which the human body acts as a source of radiation: some of the gamma rays emitted by the radionuclides in the environment interact with the atoms in our bodies by what is known as the photoelectric effect. The result is the emission of x rays by these atoms.Source
: Paul Frame, CHP, PhD