"One popular theory involves a phenomenon known as the “biofield.” The biofield is an electromagnetic field that permeates and surrounds every living being. In humans, this field extends 15 feet or more from the body, according to Ann L. Baldwin, PhD, a Reiki researcher and professor of physiology at the University of Arizona’s College of Medicine.

The heart, for example, produces an electrical field — measured through an electrocardiogram, or ECG — to regulate heartbeats. The brain also produces an electrical field, though at a lower level than the heart. In fact, every cell in the body produces an electrical charge through positive and negative charges, which then create magnetic fields.

According to this theory, the interaction between two human magnetic fields may explain the effects of touch therapies like Reiki. It is thought that the biofield is the force that guides bodily functions, and that Reiki energy influences the biofield. “[The biofield] is thought to cause dynamic changes in its vibrational qualities that alter physiological and psychological functions in living beings,” Baldwin says.

Quantum physics — the study of how small particles like electrons (particles with a negative electric charge) and photons (particles of light) behave in an attempt to explain the interactions of energy and physical matter — may also help explain how Reiki practice works. Physicists have found that these tiny particles of energy can be in more than one place at one time, and that thought or intention may change how the particles work. In other words, the Reiki practitioner may be able to gather and direct biofield energy to the recipient through thoughts and intentions. " - source: everydayhealth.com