Electrodermal screening uses electronic devices to measure the electrical resistance at numerous points on the body. This technology is not an instrument used to diagnose disease. It does however measure the electrical current moving through the acupuncture meridians and as such gives information about the bioenergetics of the body. It is an instrument of physics, not chemistry.

In the 1950's, Dr. Reinold Voll, a German doctor, observed that traditional acupuncture points had a lower electrical resistance than other skin points. He developed a device to measure the skin's resistance at these points and found that each point had a standard measurement for all healthy people. He concluded that increases from this normal reading meant there was tissue inflammation associated with that point. Decreases from the normal reading indicated there was fatigue or tissue degeneration associated with that point.

The methods and technologies developed by Dr. Voll became known as "Electro-acupuncture According to Voll" or EAV. This technology is also known as electrodermal screening or EDS. The acupuncture points that are measured are usually on the hands and feet. Specific points known as control measurement points are used to indicate the general health of an organ or tissue. There are currently over two thousand points that have been discovered.

Dr. Voll made an interesting discovery when evaluating a fellow doctor who had a history of prostate problems. Dr. Voll measured the doctor's "prostate point" and found it lower than the expected normal reading. Later that day, he measured the point again and found it to be in the normal range. At the second evaluation, the doctor had a natural remedy (homeopathic Echinacea) in his pocket. Dr. Voll discovered that abnormal readings could be corrected when a "healing medicine” was held by the person (or later placing it on a test plate that was in circuit with the patient and the instrument) he was measuring. This allowed Dr. Voll not only to find what organs were energetically unhealthy, but also what natural remedy would correct the problem, eg. homeopathic, botanical, nutritional, etc.

Various theories exist about how these machines work and what they measure. Some claim that the energy testing devices measure the amount of the qi or "life energy" that flows through the Chinese acupuncture channels. Others feel that the devices measure the amount of stress on each channel. An increase in stress will reduce the amount of electricity flowing through the channel. A natural medicine that helps resolve the stress will restore the normal flow of electricity and return the measurement to normal. Regardless, it is a fascinating phenomenon that has since become an increasingly reliable indicator in thousands of clinics worldwide.

Electrodermal screening can be very helpful with many health problems. A skilled EAV/EDS technician is able to detect the energetic signature of toxins, allergies, emotional patterns, organ "weakness", etc., in the body. EDS can also screen potential natural remedies to determine which will help restore the body's balance.

Electrodermal screening and energy medicine may be done by medical doctors, osteopaths, naturopaths, acupuncturists, chiropractors, dentists, etc. The accuracy of the screening is not 100% objective and is dependent upon the skill and experience of the practitioner. Current EDS instruments vary from simple machines to fully computerized devices.

References: 
1. Burton Goldberg Group: Alternative Medicine: The Definitive Guide. Future Medicine Publishing, Puyallup, WA; 1994. 
2. Shimmel H & Penzer V: Functional Medicine. Karl F. Haug Verlag GmbH, Heidelberg, Germany; 1996. 
3. Woodham A & Peters D: Encyclopedia of Healing Therapies, 1st ed. Dorling Kindersley, NY, NY; 1997