Some skeptics say that auras may be seen for a number of reasons such as migrarines, synesthesia, epelipsy, a disorder within the visual system, a disorder within the brain, or due to the influence of physchedelic drugs such as LSD. Another reason to see an aura is due to eye fatigue, also known as eye burn.
There have been many references to the human auras from past civilazations. In a religious art painting of Jesus, Mary and saints, there is a glowing light or halo surrounding the heads of them all. This could possibly be referring to an aura. Energy like this the life at the core of eastern religions. In China, an energy that is possibly an aura is called "Chi". In India, it's known as "Prana".
The vision of light as the source of life is in literature as well. One of the earliest writings is from the writings of Hildegard von Bingen, (1098 - 1179), who wrote visionary and theological writings throughout her life. She describes in her writings of luminous objects, as well as visionary experiences of light. These could possibly be auras.