Magnesium chloride is the most effective way of transdermal Mg intake, and in fact the only proven effective way apart from Mg sulphate baths. In the form of a cream, or applied to the skin, Mg chloride alone has been shown to be effective in raising the body's Mg levels. And the chloride ion part of Mg chloride does not displace iodine, and even indirectly helps iodine utilisation (bromine displaces iodine and chloride helps bromine excretion).

First, let's see if applying magnesium chloride through the skin is actually harmful due to the chloride part. The most abundant ion in the seas/oceans is chloride. 55% of the ions dissolved in it are chloride, meaning that water in the seas and oceans is almost 2% chloride solution! Our ancestors used to swim in it all day long, and those lucky enough to live by the water still do. It can be very harmful to have chloride ions on our skin, right? 🙂 I might add that the concentration of Mg chloride is high in seas/oceans alone, let alone in the Dead Sea, although unfortunately bromine is also high there.

Image source: Wikipedia

Obviously, it is pointless to go on about this crazy idea that chloride ions applied transdermally are harmful, when no other ion is so naturally occurring. Interestingly, however, the main difference between transdermal systemic delivery of active substances and oral delivery is that the latter can bypass the liver, as in the case of intravenous/intramuscular/subcutaneous and oral liposomal/nanocollid systems, i.e. by bypassing first-pass metabolism, so that the liver is not burdened by the active substances thus delivered, while their utilisation by the target tissues is multiplied. And chloride competes with iodide (but especially bromide/bromine) for reabsorption in the kidneys, not the liver. Therefore, oral and transdermal chloride intake should not theoretically differ in their effects on iodine. In addition, Dr. David Brownstein, today's outstanding expert in iodine therapy, recommends Mg chloride as the preferred method of Mg intake (if it does not cause diarrhea) because of its chloride content, as Dr. Sircus also considers Mg-chloride to be the best, applied transdermally. [1]

Mg chloride creams have been shown in human clinical trials to be effective and are common, inexpensive solutions for raising Mg levels, while orally bioavailable forms of magnesium are larger molecules and have questionable absorption through the skin. Even if they are absorbed, they have no benefit and no studies have yet demonstrated their effect, probably because only such low concentrations are achieved when the orally bioavailable forms are dissolved in creams that they are in practice unsuitable for Mg supplementation (more on this later). Most people are aware that they are good forms, but what a lay person obviously doesn't think about is this is a cream, while those are good oral forms, instead of transdermal, where the high molecular size and low Mg concentration are a distinct disadvantage and there is no testing behind them. And Mg chloride is certainly good and probably the best transdermally available Mg molecular form.

What is the truth about magnesium creams?

One golden rule for systemic absorption of molecules for transdermal application is that the molecule should not be much larger than 500Da, i.e. 500g/mol. The smaller the better.

The Mg chloride in a solution/cream splits into Mg ions and chloride ions. The Mg-ion has an atomic mass of 24g/mol, i.e. 24Da, which means that the Mg applied passes easily through the skin into the bloodstream. The molar mass of Mg-bisglycinate is 174g/mol, i.e. 174Da (covalently bonded, so it does not break down into Mg ions in cream/solution, but remains this large). It is also below 500Da, so it can pass through the skin, but it is 7x larger than the Mg-ion from Mg-chloride, so it is harder for it to pass through.  In addition, concentration is also important for transdermal application. Mg chloride can be made into an aqueous solution with a concentration of 54%, which is about 13% Mg. In comparison, Mg-bisglycinate can only be used to prepare a solution of up to 20% Mg with a Mg concentration of 2%. 7x the size and 6x the concentration can be achieved on the skin. There are two main aspects that determine transdermal utilisation. Until it is confirmed by testing, it is currently considered to have a utilization rate of 0. However, it is worth noting that the Mg-ion can be surrounded by a hydrate shell, which can make it difficult or even impossible to pass through the skin, so Mg chloride is only useful as a properly formulated cream, not as a smooth solution (e.g. "Mg-oil”/ancient magnesium), it can only be utilized systemically when applied to the sweat glands and hair/skin surfaces covered with hair, i.e. it is only effective when applied in this way.[3] However, an analysis published in 2017 on the efficacy of transdermal magnesium intake concluded that the efficacy of this type of Mg supplementation is highly questionable, while it also carries risks, as it bypasses the digestive system and bypasses Mg regulation.[2] Obviously, when used in small amounts, it has been shown to be safe in Mg-deficient states and should be effective.

Although I could not find any studies on the transdermal application of Mg-bisglycinate, I did find studies on the transdermal application of iron bisglycinate. It has not been found to be effective in increasing iron levels.[4] It is therefore likely that Mg-bisglycinate would not be absorbed either, especially as it would require orders of magnitude more of it to be passed through the skin than iron, since the body needs more than 10 times as much Mg.

Mg-bisglycinate and other orally good forms have not been tested and are presumably less effective than an Mg-chloride cream. Not to mention that, as I calculated above, the Mg concentration of a Mg-bisglycinate solution can be max 2%, but there are other ingredients in a cream that make it good to have 1% Mg concentration available in similar creams (data on this is usually not given in the product description). Calculated at 1%, this means a Mg concentration of 10mg/g, or 10mg/ml. Even if it were perfectly absorbed, you would still need to use 20-40ml per day to get 200-400mg of Mg, which is impossible to apply to thin areas of skin per day, and difficult even as a full body cream. (100ml of cream would run out in 2-5 days). So for this reason alone, it is pointless to use any other form of Mg in a cream other than Mg chloride. It is the best and the only one that has been proven to work, although the analysis mentioned earlier means that it should only be used in moderation, if at all.