For purposes of cellular detoxification and tissue purification, the most effective form of magnesium is magnesium chloride, which has a strong excretory effect on toxins and stagnant energies stuck in the tissues of the body, drawing them out through the pores of the skin. Chloride is required to produce a large quantity of gastric acid each day and is also needed to stimulate starch-digesting enzymes.
According to Daniel Reid, author of The Tao of Detox, magnesium sulfate, commonly known as Epsom salts, is rapidly excreted through the kidneys and therefore difficult to assimilate. This would explain in part why the effects from Epsom salt baths do not last long and why you need more magnesium sulfate in a bath than magnesium chloride to get similar results. Magnesium chloride is easily assimilated and metabolized in the human body.
In addition to its functions as an electrolyte, chloride combines with hydrogen in the stomach to make hydrochloric acid, a powerful digestive enzyme that is responsible for the breakdown of proteins, absorption of other metallic minerals, and activation of intrinsic factor, which in turn absorbs vitamin B12.
Using other magnesium salts is less advantageous because these have to be converted into chlorides in the body anyway. We may use magnesium as oxide or carbonate but then we need to produce additional hydrochloric acid to absorb them. Many aging individuals, especially with chronic diseases who desperately need more magnesium, cannot produce sufficient hydrochloric acid and thus cannot absorb the oxide or carbonate.
Chloride is a highly important and vital mineral required for both human and animal life. Without chloride, the human body would be unable to maintain fluids in blood vessels, conduct nerve transmissions, move muscles, or maintain proper kidney function. As a major electrolyte mineral of the body, chloride performs many roles, and is rapidly excreted from the body.
Magnesium chloride solution was not only harmless for tissues, but it had also a great effect over leucocytic activity and phagocytosis; so it was perfect for treatment of external wounds. – Dr. Jean Durlach
Dr. Jean Durlach et al., at the Université P. M. Curie, Paris, wrote a paper about the relative toxicities between magnesium sulfate and magnesium chloride. They write, "The reason for the toxicity of pharmacological doses of magnesium using the sulfate anion rather than the chloride anion may perhaps arise from the respective chemical structures of both the two magnesium salts. Chemically, both MgSO4 and MgCl2 are hexa-aqueous complexes. \
However MgCl2 crystals consist of dianions with magnesium coordinated to the six water molecules as a complex, [Mg(H2O)6]2+ and two independent chloride anions, Cl-. In MgSO4, a seventh water molecule is associated with the sulphate anion, [Mg(H2O)6]2 +[SO4. H2O]. Consequently, the more hydrated MgSO4 molecule may have chemical interactions with paracellular components rather than with cellular components, presumably potentiating toxic manifestations while reducing therapeutic effect."