Hair Conductivity Tests
Conducted March 17-26, 1998
The actual electrical conductivity of human hair is a factor that has
been the subject of some controversy in the field of permanent hair
removal. Some proponents of electric tweezer and home hair removal devices rely on the assertion that
hair is a conductor or semiconductor, allowing small DC (direct) currents to pass into the follicle,
producing effects similar to needle-type Electrolysis. Critics state that hair is essentially an insulator and therefore cannot conduct usable electrical currents.
To provide some insight into this issue, R.A. Fischer Company has performed in-house testing of
human hair conductivity under controlled conditions to
determine what levels of direct current flow can be measured.
METHOD OF TESTING
Four samples of human hair taken from two sites on two male subjects
were each placed into a test jig which applied DC voltages ranging from 100
volts to 5000 volts using two high-voltage electrodes. Tests were also
performed at AC (60 Hz) voltages ranging from 100 to 5000 volts for comparative
The jig was designed to minimize electrical leakage between the
electrodes and consisted of two stainless steel plates fastened to a section
of 1/16 inch thick type 94V-O printed circuit board substrate. A gap of 1/4 inch
separated the plates and one drop of Signa brand electrode cream was placed
on each plate as a conductive medium to ensure good electrical contact
between the electrodes and test hairs.
Measurements were made at 100 DC volts, 500 DC volts, 1000 DC volts,
2000 DC volts and 5000 DC volts with a series digital microammeter to first
determine the inherent leakage of the test jig. No DC leakage (measurable
above 0.1 DC microamperes) was detected during these tests, except at
the 5000 volt setting. The jig was then tested with a 1 Megohm carbon film
resistor at the 100, 500 and 1000 volt settings to verify that the measuring
apparatus was working properly.
Hairs taken from the scalp and forearm of the subjects were measured
and inserted into the jig, and then tested at the 5 preset DC voltages while
current measurements were made. The voltage was allowed to settle for 5
seconds before readings were taken at each setting.
Following the dry hair tests, all measurements were repeated with
hairs pre-soaked in each of several solutions, including:
1) Tap water
2) A 10.0 pH buffer solution
3) A solution of 50% tap water and 50% wetting agent
In each case, the hairs were immersion soaked in the test solution for 30 minutes. After soaking, each hair was taken from the immersion bath and excess solution remaining on the hair surface was removed to ensure valid measurements. (This is necessary since any solution residue remaining on the outside surface of the hair could provide a conductive path within the solution itself along the outside of the hair surface.)
Either of two methods was used to remove the excess solution on the hair surface:
1) Pre-soaked hairs were allowed to air dry for 5 minutes, OR
2) Pre-soaked hairs were gently wiped or blotted once with tissue
The test hairs were then immediately placed into the test jig and measured in each instance.
TEST EQUIPMENT USED
Copyright © 1998 R.A. Fischer Co., Inc.
- Kikusui Model TOS 8750 Withstand Voltage Tester
- Beckman Model Tech 310 Digital VOM
- Mitutoyo Dial Thickness Guage No. 7300
- Omega digital temperature meter
May not be reproduced or distributed without permission