Aura

Reading auras is like reading minds, or tea leaves, or star signs, or meridian lines — these people aren't plying a skill. They're either lying or mentally ill. An aura is a "magical field" supposedly emitted by a human body. It is claimed that some people can not only see an aura, but use it to diagnose anything from illness to mental problems.

Testing
When James Randi's $1 million challenge tested the ability of someone to identify people based on aura alone (by obscuring them behind a screen), the individual failed to correctly identify who was behind the screens. His work, therefore, was no better than a guess. It was also shown that the auras on the photos were simply moisture emitted by the skin, highlighted by a high-voltage electric current run through the subjects' bodies.

Another experiment involved an aura reader and a number of slots containing either actual people or mannequins. She was supposed to determine which slots contain real people, but she failed stating that all slots contained people.

Other explanations
Explanations for why people may claim to see auras vary wildly. The simplest case is that "aura readers" are outright liars or deluded. This is unsurprising, as people will pay good money for alternative quackery to diagnose and/or cure them. Naturalistic explanations for the apparent appearance of "auras" include:
 * visual side effects of common conditions such as - a condition where people's senses are confused or combined, such as "seeing" sounds or perceiving letters/numbers as having color, etc.
 * s which can also plausibly cause "auras".

You can see them too!
Yes, you! Just stare at your hand for a few seconds, preferably in dim light, and you'll see a light outline around it. Of course, you can easily check that it works equally well with inanimate objects. It's actually an resulting from eye tiredness. Nothing magical about it, sorry.

In reality?
Humans do give off radiation. Well, yes — but this is, in simple terms, just heat and is detected in the infra-red range. However, this is far, far beyond the detection abilities of the human eye. Some recent research in Japan has indicated that human bodies do give off light in the visible region of the electromagnetic spectrum, but at a level 1000 times lower than what the naked and unassisted human eye can detect. It is thought that this may be due to free-radical reactions in the skin, which are known to be able to emit photons at a visible frequency, but do not occur frequently enough to be detected without very specialized equipment. Internet-based idiots, of course, are quick to pounce on this sort of research, ignoring pretty much everything about the research but the eye-catching media headlines.