Your Body
Do human beings glow in the dark?
The short answer
Yes, faintly. Human bodies emit a small amount of visible light as a by-product of metabolism. Researchers imaged it with ultra-sensitive cameras in 2009. It is roughly a thousand times weaker than the human eye can detect, so nobody has ever seen it.
A Japanese team led by Masaki Kobayashi put volunteers in a light-tight room with cameras sensitive enough to count individual photons, and imaged them over several days. The people glowed. Not metaphorically — measurably, in the visible range.
The light comes from ordinary metabolism. Reactions involving free radicals produce excited molecules that shed a photon as they settle, a phenomenon called ultraweak photon emission. It is not the same as bioluminescence, which is a dedicated chemical system with a purpose. This is exhaust.
Two details make it lovely. The glow rises and falls on a daily rhythm, dimmest in the morning and brightest in the late afternoon. And it is brightest around the face — partly because faces are more exposed, and more tanned, than the rest of us.