The Illumination, by Kevin Brockmeier
In the opening pages of The Illumination, a woman cuts her finger with a knife and the wound emits a silvery light. At the hospital, she learns that this is happening all over the world—every site of injury, pain or sickness shines. A headache looks like a glowing orb, arthritic bones look like icy branches, a kidney stone is a ball of light barely visible underneath a shirt, open wounds are blinding.
The media call this event, when all the world's pain becomes permanently visible, the Illumination. At first a phenomenon, then cause for a media frenzy and hailed by some as a sign of the apocalypse, the glow quickly becomes the new normal. One might assume that the world would become more empathetic as a result of it, but if anything the characters in this novel become more insular.