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.  Parents of children with autism frequently use Epsom salts baths or creams because of the sulfate, which they are usually deficient in due to metabolic issues. Sulfate is also crucial to the body and is wasted in the urine of autistic children.
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. This is a powerful hydrotherapy that draws toxins from the tissues, replenishes the “vital fluid” of the cells, and restores cellular magnesium to optimum levels. Magnesium chloride is environmentally safe, and is used around vegetation and in agriculture. It is not irritating to the skin at lower concentrations, and is less toxic than common table salt.
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 external wounds treatment.
Dr. Jean Durlach et al, at the Université P. et M. Curie, Paris, wrote a paper about the relative toxicities between magnesium sulfate and magnesium chloride. They write, “The reason of the toxicity of magnesium 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.”
MgSO4 is not always the appropriate salt in
clinical therapeutics. MgCl2 seems the better
anion-cation association to be used in many
clinical and pharmacological indications. 
Dr. Jean Durlach et al
Magnesium chloride is stronger than Epsom salts by a factor with only the barest trace of any heavy metals (varies by source with the Zechstein’s underground salt lake yielding the most pristine MgCl).
Chloride is an “essential” mineral for humans.  It is abundant in ionic trace mineral preparations. It is a major mineral nutrient that occurs primarily in body fluids. Chloride is a prominent negatively charged ion of the blood, where it represents 70% of the body’s total negative ion content. On average, an adult human body contains approximately 115 grams of chloride, making up about 0.15% of total body weight. The suggested amount of chloride intake ranges from 750 to 900 milligrams per day, based on the fact that total obligatory loss of chloride in the average person is close to 530 milligrams per day.
As the principle negatively charged ion in the body, chloride serves as one of the main electrolytes of the body. Chloride, in addition to potassium and sodium, assists in the conduction of electrical impulses when dissolved in bodily water. Potassium and sodium become positive ions as they lose an electron when dissolved and chloride becomes a negative ion as it gains an electron when dissolved. A positive ion is always accompanied by a negative ion, hence the close relationship between sodium, potassium and chloride. The electrolytes are distributed throughout all body fluids including the blood, lymph, and the fluid inside and outside cells. The negative charge of chloride balances against the positive charges of sodium and potassium ions in order to maintain serum osmolarity.
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 break down of proteins, absorption of other metallic minerals, and activation of intrinsic factor, which in turn absorbs vitamin B12. Chloride is specially transported into the gastric lumen, in exchange for another negatively charged electrolyte (bicarbonate), in order to maintain electrical neutrality across the stomach membrane. After utilization in hydrochloric acid, some chloride is reabsorbed by the intestine, back into the blood stream where it is required for maintenance of extracellular fluid volume. Chloride is both actively and passively absorbed by the body, depending on the current metabolic demands.  A constant exchange of chloride and bicarbonate, between red blood cells and the plasma helps to govern the pH balance and transport of carbon dioxide, a waste product of respiration, from the body. With sodium and potassium, chloride works in the nervous system to aid in the transport of electrical impulses throughout the body, as movement of negatively charged chloride into the cell propagates the nervous electrical potential.
Deficiency of chloride is rare. However, when it does occur, it results in a life threatening condition known as alkalosis, in which the blood becomes overly alkaline. A tedious balance between alkalinity and acidity is in constant flux, and must be vigilantly maintained throughout the entire body. Alkalosis may occur as a result of excessive loss of sodium, such as heavy sweating during endurance exercise, and in cases of prolonged vomiting and diarrhea. Symptoms include muscle weakness, loss of appetite, irritability, dehydration, and profound lethargy. Hypochloremia may result from water overload, wasting conditions, and extensive bodily burns with sequestration of extracellular fluids. In a situation in which infants were inadvertently fed chloride-deficient formula, many experienced failure to thrive, anorexia, and weakness in their first year of life.
Excessive intakes of dietary chloride only occur with the ingestion of large amounts of salt and potassium chloride. The toxic effects of such diets, such as fluid retention and high blood pressure, are attributed to the high sodium and potassium levels. Chloride toxicity has not been observed in humans except in the special case of impaired sodium chloride metabolism, e.g., in congestive heart failure. Healthy individuals can tolerate the intake of large quantities of chloride provided that there is a concomitant intake of fresh water. Other situations in which increased blood levels of chloride are seen include diseases of improper waste elimination that occur in kidney diseases. Excess chloride is normally excreted in the urine, sweat, and bowels. In fact, excess urinary excretion of chloride occurs in high salt diets. Excessive intakes of chloride can occur in a person with compromised health in addition to an unhealthy diet. However, those that follow a healthy diet and lead an active lifestyle may need to consider supplementing their diet with this important mineral.
The mineral supplement chloride is very different from the gas chlorine. While elemental chlorine is a dangerous gas that does not exist in the free elemental state in nature because of its reactivity, although it is widely distributed in combination with other elements. Chloride is related to chlorine however, as one of the most common chlorine compounds is common salt, NaCl. Chloride is a byproduct of the reaction between chlorine and an electrolyte, such as potassium, magnesium, or sodium, which are essential for human metabolism.  Chloride salts are essential for sustaining human metabolism and have none of the effects of isolated chlorine gas.
Chloride occurs naturally in foods at levels normally less than 0.36 milligrams per gram of food. The average intake of chloride during a salt-free diet is approximately 100 milligrams per day. Unfortunately, chloride is found commonly combined with undesirable dietary sources. The most common of these negative sources is table salt. Table salt is made from a combination of sodium and chloride ions. Other unhealthful sources include yeast extracts, processed lunch meats, and cheeses. Healthier sources of chloride include kelp (seaweed), ionic trace minerals, olives, rye, tomatoes, lettuce, and celery, although not in large enough amounts to supply the needs of an active adult. In its original form, however, chloride is leached from various rocks into soil and water by years of weathering processes. The chloride ion is highly mobile and is transported to closed basins, such as the Great Salt Lake, or oceans.
In summary, chloride is a highly important, 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. Active adults that eat a healthy diet devoid of salt and illnesses in which vomiting and/or diarrhea are profuse warrant the supplementation of additional chloride. Replacement of chloride is essential on a daily basis to maintain regular metabolic function. The body safely utilizes without negative health effects. Negative health effects associated with diets high in chloride are mainly attributable to sodium and potassium, the other two electrolyte minerals to which chloride is often attached. 
Researches also studied ionic fluxes in the two directions between the mother and the fetus. They found that there was a greater positive effect when MgCl2 was used, and that MgSO4 could not guarantee the fetal needs in sodium and potassium exchange like MgCl2 could. They also found that MgCl2 interacts with all the exchangers in the cell membrane, while the effect of MgSO4 is limited to paracellular components without interaction with cellular components. Dr. Durlach summarized saying, “MgCl2 interacts with all exchangers while the interaction of MgSO4 is limited to paracellular exchangers, and MgCl2 increases the flux ratio between mother to fetus while MgSO4 decreases it.”
High-dosage, tocolytic magnesium sulfate (MgSO(4)) administered to pregnant women during pre-term labor can be toxic, and sometimes lethal, for their newborns.
Chloride is required to produce a large quantity of gastric acid each day and is also needed to stimulate starch-digesting enzymes. 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 then cannot absorb the oxide or carbonate.
Sulfate is also important and has an influence over almost every cellular function. Sulfate attaches to phenols and makes them less harmful, and sets them up for being excreted from your kidneys. A lot of these potentially toxic molecules are in food. Sulfate is also used to regulate the performance of many other molecules. Many systems in the body will not function well in a low-sulfate environment. Sulfur is so critical to life that the body will apparently borrow protein from the muscles to keep from running too low.
Though magnesium sulfate will save your life in emergency situations as quickly and easily as magnesium chloride, magnesium chloride fits the bill as a universal medical nutrient. Magnesium sulfate is a close cousin whose effect, form, and toxicity requires that it be used in special applications when the sulfur is needed.
It is good to know that magnesium chloride will provide the chlorides (without the sodium) needed to eliminate bromides, which is also necessary to any successful detoxification program. “Chloride competes with bromide at the renal level and increases the renal clearance of bromide thus magnesium chloride is ideal for magnesium supplementation. Some patients require up to 2 years of iodine therapy to bring post loading urine bromide levels below 10 mg/24 hr, if chloride loading is not included in the bromine detoxification program.” 
Dr. David Brownstein promotes the use of magnesium as a supplement “synergistic” to treatment with iodine. “As with using any nutritional supplement, a comprehensive holistic treatment plan provides the best results. Magnesium is an important part of the iodine treatment plan. Magnesium deficiency is very common. Magnesium is nature’s relaxing agent. Magnesium levels (via red blood cell magnesium levels) should be assessed and supplementation instituted. Magnesium supplementation will likely ensure optimal results with iodine.” 
 Magnesium Research. Volume 18, Number 3, 187-92, September 2005, original article
 Chloride: The Forgotten Essential Mineral
By Chris D. Meletis, N.D.; 2003.
 Mittendorf R, Dammann O, Lee KS. Brain lesions in newborns exposed to high-dose magnesium sulfate during preterm labor. Department of Obstetrics and Gynecology, Loyola University Medical Center, Maywood, IL, USA. J Perinatol. 2005 Dec 1; doi:10.1038/sj.jp.7211419.
 Rauws, A.G., Pharmacokinetics of Bromide Ion-An Overview. Fd. Chem. Toxic., 21:379-382, 1983
 Iodine and Chelation; Mark Sircus Ac., OMD; http://www.alkalizeforhealth.net/Liodine2.htm
 Iodine, the Rest of the Story; David Brownstein MD;