Magnesium chloride is one of the most versatile salts in commercial use, showing up in everything from winter road treatments and tofu production to dietary supplements and experimental energy storage systems. It dissolves readily in water, absorbs moisture from the air, and melts ice at temperatures well below what ordinary table salt can handle. That combination of properties makes it enormously useful, but also introduces trade-offs that matter depending on how you encounter it.
Where Magnesium Chloride Comes From
Magnesium chloride occurs naturally in seawater, underground brine deposits, and mineral-rich lakes. The Dead Sea is one of the most famous sources: the chemical industry in Israel has long extracted potassium chloride, sodium chloride, magnesium chloride, bromine, and magnesium oxide from its concentrated brines.1Elsevier. Utilization of the dead sea minerals (a review) The mineral bischofite, a naturally occurring hydrated form of magnesium chloride, is mined in places like Chile and Russia. In other regions, magnesium chloride is produced from seawater evaporation or as a byproduct of other mineral processing. The compound is inexpensive to produce and ships easily as either a liquid brine or dry flakes, which helps explain its widespread adoption.
The Go-To Deicer for Extreme Cold
Rock salt (sodium chloride) is the cheapest and most common road deicer, but it stops working effectively around -9 °C (about 15 °F). Magnesium chloride keeps melting ice down to roughly -33 °C (-27 °F), making it the preferred choice in places that see genuinely harsh winters. It also works faster than rock salt in the critical first minutes after application, because its hygroscopic nature draws moisture and forms a brine layer quickly.
Many state and provincial transportation departments in cold-climate regions spray liquid magnesium chloride on roads before a storm, a practice called anti-icing. Pre-wetting the pavement prevents ice from bonding to the surface in the first place, which reduces both the total amount of chemical needed and the number of plow passes. The result is often safer roads with less environmental loading than dumping heavier quantities of rock salt after the fact.
The Downside for Concrete and Steel
The same aggressiveness that makes magnesium chloride a powerful deicer also makes it hard on infrastructure. In laboratory tests comparing common deicing salts, magnesium chloride was the most destructive to highway concrete, worse than calcium chloride and far worse than sodium chloride under most conditions.2Environmental & Engineering Geoscience. Experimental Deterioration of Highway Concrete by Chloride Deicing Salts The mechanism involves a chemical reaction between magnesium ions and the calcium compounds in cement paste, which gradually converts the hard binder into a softer, weaker material. Over many winters, bridge decks, parking garages, and curbs in magnesium-chloride-treated areas can show accelerated scaling and spalling.
Metals take a hit too. Field and laboratory studies exposing common structural metals to a 25 percent magnesium chloride solution found that mild carbon steel suffered the most surface rust and weight loss, while aluminum alloy was vulnerable to deep penetration of corrosion into its matrix.3Case Studies in Construction Materials. Corrosion of metals exposed to 25% magnesium chloride solution and tensile stress: Field and laboratory studies Stainless steel held up better, though even it corroded more when under tensile stress. For anyone living in a region where magnesium chloride is sprayed on roads, the practical takeaway is familiar: wash your car’s undercarriage regularly during winter.
An interesting wrinkle involves brake components. Research on gray cast iron exposed to deicing salts found that corrosion scales initially acted as abrasive particles, then crushed and spread to form a kind of solid lubricant. On a titanium-based composite, no corrosion scales formed, but magnesium chloride deposits absorbed moisture from the air, liquefied, and maintained a persistent lubricating effect on the surface. Sodium chloride deposits, by contrast, tended to remain dry.4Tribology International. Effects of the exposure to corrosive salts on the frictional behavior of gray cast iron and a titanium-based metal matrix composite This hygroscopic behavior is a recurring theme with magnesium chloride: its hunger for water affects everything it touches.
Keeping Dust Down on Unpaved Roads
That same moisture-grabbing property is exactly what makes magnesium chloride useful for dust control. Unpaved roads generate enormous amounts of airborne dust, which damages vehicles, degrades air quality, and erodes the road surface itself. When magnesium chloride (often applied as bischofite) is spread on a gravel road, it pulls water from the atmosphere and keeps the surface damp, binding fine particles together.
Field trials on unpaved road sections treated with bischofite showed substantial reductions in both surface roughness and dust emission compared to untreated gravel, with the effect persisting over an 18-month monitoring period.5Transportation Research Record: Journal of the Transportation Research Board. Evaluation of the Use of Magnesium Chloride for Surface Stabilization and Dust Control on Unpaved Roads Mining operations, rural municipalities, and military bases in arid regions all use magnesium chloride for this purpose. It is not a permanent fix, because rain eventually washes the salt away, but reapplication is straightforward and relatively cheap.
Tofu and Other Food Uses
If you have ever eaten Japanese-style tofu, you have almost certainly consumed magnesium chloride. Sold in food-grade form as nigari (the liquid left after sea salt crystallizes), it is one of the traditional coagulants used to curdle soymilk into tofu. The magnesium ions interact with soy proteins, causing them to aggregate and form a gel.
The process is concentration-dependent in ways that matter to tofu makers. Laboratory work has mapped out the stages: at very low magnesium chloride concentrations, soymilk does not coagulate at all. Between about 3 and 8 millimoles per liter, curds begin to form. The coagulation stabilizes across a wide middle range and then, at very high concentrations, actually reverses as the curds dissociate again.6LWT. Effect of magnesium chloride concentration on soymilk coagulation mechanism This is why experienced tofu makers add nigari carefully and stop at the right point: too much and you lose the curd structure rather than strengthening it. Compared to calcium sulfate (gypsum), another common coagulant, magnesium chloride tends to produce a softer, silkier tofu with a slightly more delicate flavor.
Beyond tofu, food-grade magnesium chloride appears as a firming agent in canned vegetables, a nutrient fortifier in certain processed foods, and occasionally as a mineral additive in bottled water marketed in parts of Asia.
Magnesium Supplements and How Well They Absorb
Magnesium chloride is one of many forms of magnesium sold as a dietary supplement, alongside magnesium oxide, citrate, glycinate, and others. A question that comes up constantly in health forums is which form absorbs best. The honest answer is that the differences are smaller than marketing would have you believe.
A review of the evidence on magnesium bioavailability concluded that the type of magnesium salt appears less important than commonly thought. Some studies found slightly higher absorption from organic magnesium salts compared to inorganic ones, while others did not. The dose you take and your existing magnesium status matter more than the chemical form on the label.7PubMed Central. Intestinal Absorption and Factors Influencing Bioavailability of Magnesium-An Update A separate systematic review did suggest that, as a group, inorganic formulations (which include magnesium chloride and magnesium oxide) tend to be slightly less bioavailable than organic ones (like citrate or glycinate), and that the percentage absorbed drops as the dose increases.8PubMed. Bioavailability of magnesium food supplements: A systematic review
Within the inorganic category, magnesium chloride generally performs reasonably well because it dissolves easily and releases magnesium ions in the stomach. Magnesium oxide, by contrast, is poorly soluble, which is one reason its absorption tends to be lower despite containing more elemental magnesium per tablet. One study did find that enteric-coated magnesium chloride tablets absorbed much less magnesium than a simple magnesium acetate solution, suggesting that the coating itself can impair uptake regardless of the salt form.9JCI Insight. Intestinal absorption of magnesium from food and supplements So the delivery format can matter as much as the chemistry.
For most people who are mildly low in magnesium, a standard oral magnesium chloride supplement taken with food is a reasonable option. It is not magic, and it is not clearly superior to magnesium citrate or glycinate, but it works. Taking smaller doses spread across the day tends to improve absorption compared to one large dose.
The Transdermal Magnesium Myth
Magnesium chloride is widely sold as bath flakes, foot-soak crystals, and spray-on “magnesium oil” (which is not actually an oil but a concentrated brine that feels slippery on skin). The marketing claim is that soaking in or spraying on magnesium chloride lets your body absorb magnesium through the skin, bypassing the gut. This claim is popular but scientifically shaky.
A review of the available evidence on transdermal magnesium concluded that the idea is scientifically unsupported.10PubMed Central. Myth or Reality-Transdermal Magnesium? The outer layer of skin, the stratum corneum, is a remarkably effective barrier against charged ions like magnesium. An ex vivo study measuring actual magnesium permeation through human skin found minimal passage across intact skin, with no meaningful difference between magnesium-treated and control samples. Only when the skin barrier was deliberately disrupted (by tape-stripping away the outer layer) did magnesium permeation increase dramatically, by several orders of magnitude.11PubMed. Does magnesium permeate the skin? An ex vivo investigation of magnesium ion delivery through intact and barrier-disrupted skin
That said, people with compromised skin barriers, whether from eczema, abrasions, or other conditions, could theoretically absorb more. And many users report that magnesium chloride baths feel relaxing, reduce muscle tension, or help with sleep. Whether those effects come from magnesium absorption, the warmth of the bath, placebo, or some other mechanism is an open question. If you enjoy Epsom salt or magnesium chloride soaks, there is little harm in them, but treating them as a reliable way to correct a magnesium deficiency is not supported by the current evidence.
Skin Benefits From Mineral-Rich Bathing
Even if magnesium does not cross intact skin efficiently enough to raise blood levels, there is evidence that it can benefit the skin itself. A study on people with atopic dry skin (the kind associated with eczema) had volunteers soak a forearm in a 5 percent Dead Sea salt solution, which is rich in magnesium chloride, for 15 minutes. Compared to soaking in plain tap water, the mineral bath significantly improved skin barrier function, increased hydration of the outer skin layer, and reduced both roughness and redness.12PubMed. Bathing in a magnesium-rich Dead Sea salt solution improves skin barrier function, enhances skin hydration, and reduces inflammation in atopic dry skin The researchers attributed the effect primarily to the high magnesium content.
This fits with the long tradition of people with skin conditions traveling to the Dead Sea for therapeutic bathing. The distinction worth keeping in mind is that skin-level benefits and systemic absorption are two different things. A magnesium-rich soak can help your skin without necessarily raising the magnesium levels inside your body.
What Happens When You Get Too Much
For healthy people with normal kidneys, excess magnesium from food or standard supplements is handled easily: the kidneys excrete what the body does not need. Problems arise when kidney function is impaired or when someone takes an unusually large dose. Hypermagnesemia, the clinical term for dangerously elevated blood magnesium, can cause muscle weakness, low blood pressure, respiratory depression, cardiac arrhythmias, and in extreme cases, coma.13PubMed Central. Hypermagnesemia in Clinical Practice
A case report in the forensic literature describes a fatal outcome from oral ingestion of magnesium chloride dissolved in milk, taken as a folk remedy. The individual’s posthumous serum magnesium was 10.2 mg/dL, well above the normal range of roughly 1.7 to 2.2 mg/dL, and the cause of death was attributed to hypermagnesemia.14PubMed. A fatal case of hypermagnesemia caused by ingesting magnesium chloride as a folk remedy Cases like this are rare but serve as a reminder that magnesium chloride is a potent salt, not a harmless tonic. People with kidney disease, the elderly with declining renal function, and anyone on medications that affect kidney clearance should be cautious with magnesium-containing supplements and especially with concentrated solutions used as home remedies.
Metabolic Health Effects in Clinical Trials
On the positive side of the health ledger, controlled trials have examined oral magnesium chloride supplementation in specific populations. One randomized, double-blind, placebo-controlled trial looked at people who were metabolically obese but normal-weight, a group that carries excess metabolic risk despite not appearing overweight. After supplementation with magnesium chloride, the supplemented group showed meaningful improvements in several markers: systolic and diastolic blood pressure dropped compared to the placebo group, fasting glucose fell, insulin resistance improved substantially, and triglyceride levels decreased sharply.15PubMed. Oral magnesium supplementation improves the metabolic profile of metabolically obese, normal-weight individuals: a randomized double-blind placebo-controlled trial
These results are striking but come from a specific population and a single trial, so they should not be over-generalized. Broader research on magnesium and metabolic health consistently suggests that adequate magnesium intake is associated with lower risk of type 2 diabetes and better blood pressure control, but the effects of supplementation are most pronounced in people who are deficient to begin with. If your magnesium levels are already normal, popping extra magnesium chloride tablets is unlikely to produce dramatic metabolic changes.
Industrial Applications Beyond Roads
Magnesium chloride plays a role in several industrial processes that rarely make the consumer spotlight. One of the more interesting is Sorel cement, a type of magnesium oxychloride cement made by mixing magnesium oxide with a concentrated magnesium chloride solution. The resulting material is strong, quick-setting, and bonds well to a variety of aggregates including wood chips and stone dust. Microscopic analysis shows that the cement’s crystalline structure consists of needle-shaped crystals bundled together with a dense, granular surface at the nanoscale, which contributes to high compressive strength.16Advances in Cement Research. Microstructures of magnesium oxychloride Sorel cement Sorel cement has been used for industrial flooring, fire-resistant panels, and decorative applications. Its weakness is water sensitivity: prolonged exposure to moisture can degrade the cement, which limits its use to interior or protected environments.
Magnesium chloride hexahydrate, the form of the salt that holds six water molecules in its crystal structure, has also attracted attention as a thermochemical energy storage material. The idea is that the hydrated salt can store heat energy by releasing its water when heated, then release that energy later by reabsorbing moisture from the air. Research has characterized its thermal properties, finding that the material can achieve stable heat output for over four hours under controlled humidity and airflow conditions.17Solar Energy Materials and Solar Cells. Thermophysical characterization of magnesium chloride and its application in open sorption thermal energy storage system The appeal for building-scale energy storage is that magnesium chloride is cheap, abundant, and nontoxic compared to many alternative phase-change and thermochemical materials.18Energy Technology. Experimental Study of MgCl2 ⋅ 6 H2O as Thermochemical Energy Storage Material The technology is still in the experimental stage, but the concept of using a common salt to store surplus solar or waste heat and release it on demand is appealing in a world looking for affordable ways to manage renewable energy intermittency.
Neuroprotective Research
Magnesium’s role in the nervous system has prompted some investigation into whether magnesium salts can protect brain tissue during oxygen deprivation. In animal research using newborn piglets as a model, magnesium sulfate infusion during cerebral hypoxia preserved the number and binding characteristics of a key brain receptor that is involved in excitatory signaling and can contribute to brain damage when overstimulated during oxygen deprivation. Piglets that received magnesium maintained receptor levels close to normal, while untreated hypoxic piglets showed significant declines.19Elsevier / Brain Research. Protective effect of MgSO4 infusion on NMDA receptor binding characteristics during cerebral cortical hypoxia in the newborn piglet While this study used magnesium sulfate rather than magnesium chloride, the active agent is the magnesium ion itself; the sulfate and chloride simply serve as the delivery vehicle. This line of research is part of a broader clinical interest in magnesium for neonatal neuroprotection, and intravenous magnesium sulfate is already used in obstetric settings for both preeclampsia management and fetal brain protection before anticipated preterm delivery.
Translating neuroprotective findings from animal models to routine clinical use in adults remains a work in progress, and oral magnesium chloride supplements should not be mistaken for a brain-protection therapy. But the underlying biology, the way magnesium ions modulate excitatory signaling and help prevent neurons from being overstimulated, is well established and helps explain why adequate magnesium matters for neurological health in general.
Environmental Considerations
Any salt applied to roads in large quantities eventually ends up somewhere else: in soil, groundwater, streams, and lakes. Magnesium chloride is generally considered less harmful to vegetation than sodium chloride, because magnesium is a plant nutrient while sodium is toxic to most plants at elevated levels. But “less harmful” is not the same as harmless. Concentrated runoff from heavily treated roads can raise chloride levels in nearby waterways, and aquatic organisms are sensitive to chloride regardless of which cation it is paired with. Some regions have begun monitoring chloride loading in watersheds and adjusting application rates accordingly.
On the soil side, magnesium chloride can alter soil structure. Magnesium ions can displace calcium and other cations on clay particles, which in some soil types leads to reduced permeability and increased compaction. For dust control on unpaved roads, this compaction is actually the point, but for adjacent agricultural land it can be a concern. The overall environmental footprint depends heavily on application rate, climate, drainage patterns, and proximity to sensitive habitats. In most settings, the amounts used for deicing or dust control are manageable, but the effects are worth tracking over the long term, especially as climate change pushes some regions toward heavier winter storm cycles and more frequent chemical applications.