I don't believe in auras, but perhaps some of these photons are picked up by human brains unconsciously, even though it can not be seen "directly". Those that sense it feel special because it is not common, and may use supernatural explanations, when it is really just a natural phenomenon.
If humans could detect this light then we could see living things in otherwise complete darkness. But we cannot. So it stands to reason that these photons do not explain "auras", and "It's just your imagination" remains the best explanation for auras. Perhaps they are based on simple after-images: if you stare at something long enough the color detecting cells in your eyes get tired and you start seeing weird visual effects that seem to match how people describe "auras".
No one ever claimed that auras weren't natural, just frequencies that most people can't see. Everything vibrates, even physical matter, we've just agreed to experience some frequencies differently.