Current limitation in hair electrolysis removal circuit

Question

NOTE: Added by moderator.
The voltages and currents when applied as described in this question (no more than 9 VDC) would be considered safe under almost any regulatory system. Higher voltages and currents and/or puncturing the surface skin with an electrode in the vicinity of the heart may have dangerous consequences.

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Galvanic electrolysis is a technique of permanent hair removal where an electrode is applied to the hair follicle. The chemical reaction results in lye produced which destroys the follicle.

• Voltage used is 9V DC.

• Target current is 0.1mA to 0.8mA

Some folks have designed diy circuits and I am concerned by the fact that their designs assume the resistance of the body is that of wet skin (around 7000 Ohm). What if the needle is accidentally probed into a blood vessel. That will drop the resistance down to, say, 200 Ohms, and given the same voltage source, might drive lethal currents.

Now I imagined that instead of relying on the body to provide the bulk of resistance, and add whatever extra is needed using a resistor in series to drive a suitable current, isn't a design where the body's resistance in a very minor contribution and the bulk from the resistor better?

Normally the patient (or yourself, in diy) keep a salty wet sponge under your foot to complete the circuit. So the current pathway is from hair follicle to foot with sponge. That means, if the hair is on your left arm, the current pathway will include the heart! I expect a design where a ground wet salty sponge is attached to an area close to the hair follicle being treated, with the feet insulated from ground, a better way to protect the heart and vital organs. This obviously will bring the resistance down a great deal, given the short distance between the "terminals". But we can always attach a much larger resistor in series, and since that is fixed, it will also take care of the possible high current issue.

The usual (dangerous) circuit

My proposed (hopefully safer) circuit, where R is much greater than the R in above circuit.

Is my train of thought correct? What is a possible fault situation in my hopefully better safer setup?

EDIT 1: On @RussellMcMahon request, I state that the voltage source is 9V DC, and the intended current should never exceed 0.8mA. I am open to complex circuitry involving op amps, FET's, MOSFET's, transistors and such, but please ALSO give a comment on my presented setup above.

Answer 1

My stack exchange answer here provides a very detailed discussion of the dangers incurred by applying low voltages (say 12 VDC) to the body in various manners. The cited references, including

• A review of hazards associated with exposure to low voltages

  A review of hazards associated with exposure to low voltages Dr. Marom Bikson Department of Biomedical Engineering, City College of New York of the City University of New York The Graduate School and University Center of the City University of New York New York, N.Y

and

• Electrocution related fatalities

Make it very clear that fatal electrocution can occur with extremely low voltage sources and, very importantly, the conditions under which such events occur are very rare and require exceptional circumstances.

This article cited in my prior answer provides this diagram. This relates to "GFCI" equipment which breaks contact under shock conditions but is useful here. Current is on the X axis and acceptable skin application lie on the Y axis. Currents of under 6 mA via the skin have application time regulatory requirements of 2+ seconds. Note the red heart fibrillation curve - far higher currents for much longer durations.

So

I would hazard a professional guestimate, with no certainty that I was correct and no responsibility taken that:

• The usual method of wet sponge under foot is unwise but almost certainly not going to cause a fatality. Not using it hear the heart and not puncturing the skin there "would be wise" but if currents are kept to the maximum level stated the dangers are very very very low.

and that

• Your described method sounds safer again. If a small 9V "PP3" transistor radio battery is used with a series resistor of say 1000 Ohms then maximum possible current is I = V/R = 9/1000 = 9 mA which is not dangerous if applied to the skin surface.

• Two sharp electrodes pushed into the skin adjacent to the heart "just may" cause problems but in most cases the sharp electrode issues would predominate. It's certainly not something that you should try.

• Currents in the microamps level applied internally in the vicinity of the heart can be fatal.