# Current limitation in hair electrolysis removal circuit

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.

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.

• You could use a current source instead of a voltage source + resistance. That way you do not need to make any assumptions regarding the body resistance. Disclaimer:I have no experience in medical electronics.
– sai
Commented Aug 22 at 13:41
• Your train of thought regarding changing the terminal position sounds reasonable to me but again, I am no expert and given that the subject is a person, I think it would make sense to add more circuit complexity and ensure that there is no risk.
– sai
Commented Aug 22 at 14:20
• What voltage ? What target current? Killing people is surprisingly easy. Sometimes it doesn't happen for enough trials that people become blasé / assume it is safe. || We can give good answers with enough information. As it is we don't know if we are offering advice that may make us morally and/or legally culpable for damage caused. SO Please answer at least the two above questions. || A current source need not be complex or difficult. ||**NOTE** Due to the issues involved I will close this question if more detail is not provided promptly. Not wanting to seem harsh, but, its important. Commented Aug 22 at 14:51
• This is not the type of device to DIY. Medical electronics are subject to strict requirements and thats not for fun. It's because the human body is complex, and potential risks can have fatal outcomes. Development of medical devices actually to be used on living things should be left to those who have the proper competence, imo. Commented Aug 22 at 15:35
• @RussellMcMahon Voltage is 9V DC only, target current is stated in question. And instead of closing the question, please give a good answer. It will save lives! Lack of information is mostly why diy'ers get into trouble. Not having information doesn't stop them. Mind as well provide our best discussion so they can use it. Commented Aug 22 at 17:21

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

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.

• Sigh, I had forgotten about this place since the question was closed. Never knew it can re-open... Commented Sep 5 at 11:06
• Your write-up was very interesting. I still am confused as to whether current can pass through your heart if the two electrodes, EVEN IF they have punctured the skin, are a centimeter apart from each other and this place being, say, your forearm or calves. There is no path to ground from the (-)ive terminal through your heart if you wear rubber sandals, except that of the other adjacent electrode. Even if there was, it would have a resistance way larger than of the short path between electrodes, thus majority of current would flow safely. Could cause burns, sure, but death?! Commented Sep 5 at 11:13
• @ElFlea the current you are talking about is extremely small by electric shock measures. See graph in my answer. You are not going to cause burns from momentary into skin injection but of course it's inadvisable.. If you left the electrodes in your skin you would form very sow elevtrolysis which would leave some sort of adverse results but probably relatively minor. I would be very very very very surprised if doing such thing caused heart issues. You can for example apply a 9 volt battery to your tongue. This is quite unpleasant but I have ... Commented Sep 5 at 11:18
• never ever heard of its causing any adverse effects in the body. I test nine volt batteries this way very very occasionally. Commented Sep 5 at 11:18
• I know it the current I talk about is extremely small. I'm confused about you mentioning that such currents applied INTERNALLY can cause ventricular fibrillation. Now is it even physically possible for current at all going to your heart if the voltage is applied between two very close points on an extremity like the forearm? I believe there is NO chance of even minor electrical current to the heart. Even if everything failed, the circuit shorted say, the skin/tissue between the electrodes would burn, but the heart would be safe, right? Commented Sep 5 at 12:04