Epsom salt is not magnesium chloride. Epsom salt is magnesium sulfate (MgSO4), a different chemical compound. Both contain magnesium, but they pair it with different molecules, which changes how they behave in your body and how you’d use them. The two are often confused because they look similar and are both sold as bath soaks and supplements.
The Chemical Difference
Magnesium sulfate, the compound in Epsom salt, combines magnesium with sulfur and oxygen. Magnesium chloride combines magnesium with chlorine. That distinction matters more than it sounds. The sulfate portion of Epsom salt draws water into your intestines when taken orally, which is why it works as a laxative. The chloride form behaves differently in your digestive system and is generally better absorbed when swallowed as a supplement.
In their crystallized forms, the two compounds even hold water differently. Epsom salt crystals naturally bind with seven water molecules, forming coarse, grainy crystals. Magnesium chloride binds with six water molecules and is typically sold as flat, irregular flakes rather than granules. If you’ve seen “magnesium flakes” at a store, those are almost always magnesium chloride.
Where Each One Comes From
Most Epsom salt on the market is synthetically manufactured, though it can also be sourced from naturally occurring mineral springs. The name comes from Epsom, England, where the compound was first identified in spring water centuries ago.
Magnesium chloride is a naturally occurring mineral mined from ancient seabeds or harvested from mineral-rich bodies of water like the Dead Sea. One well-known source is the Zechstein seabed in the Netherlands, a deposit that has been sealed underground for roughly 250 million years. Magnesium chloride can also be produced synthetically, but many brands market the naturally mined versions as higher purity.
How Well Your Body Absorbs Each Form
If you’re taking magnesium orally to raise your levels, the form matters. Magnesium chloride is well absorbed in the digestive tract, making it a solid option as a general supplement. Magnesium sulfate is poorly absorbed by comparison. Both are classified as inorganic magnesium salts, which as a group tend to have lower bioavailability than organic forms like magnesium citrate. But within that inorganic category, chloride outperforms sulfate for oral supplementation.
The sulfate in Epsom salt is actually part of what makes it a laxative. Because magnesium sulfate isn’t easily absorbed, it stays in the intestinal tract and pulls water in through osmosis. That increased fluid loosens stool and speeds things along. This is useful if constipation relief is the goal, but it means very little of the magnesium actually reaches your bloodstream.
Do Bath Soaks Actually Work?
This is where things get murky for both compounds. The idea behind Epsom salt baths and magnesium flake baths is that magnesium absorbs through your skin, raising your body’s magnesium levels and relaxing your muscles. The scientific evidence for this is weak.
One often-cited study had 19 people bathe in Epsom salt solutions for 12 minutes a day over seven days. Blood magnesium levels did rise, from an average of about 105 parts per million before bathing to 141 ppm after a week. But the study had no control group and has been criticized for its methodology. A more rigorous study using isolated human skin found that magnesium chloride solution allowed only about 6 micrograms of magnesium to pass through the skin over 24 hours, barely more than plain water. Magnesium creams performed somewhat better, but the amounts were still small.
A 2017 review published in the journal Nutrients examined the available evidence and concluded there’s no strong proof that either form of magnesium is meaningfully absorbed through the skin. That doesn’t mean bath soaks are useless. Warm water itself relaxes muscles, reduces joint stiffness, and lowers stress. Many people feel genuinely better after a soak. The benefit may just come from the bath rather than the magnesium.
Which One to Use for What
Your choice depends on what you’re trying to accomplish.
- For a bath soak: Either works. Epsom salt is cheaper and more widely available. Magnesium chloride flakes are often marketed as superior for skin absorption, but the evidence doesn’t strongly support that claim. A typical magnesium flake bath calls for about 250 grams (roughly two cups) soaked for at least 20 minutes. Epsom salt baths use similar amounts, often one to two cups.
- For raising magnesium levels: Magnesium chloride taken orally is the better choice. It absorbs well in the gut and is available in capsule, tablet, and liquid forms. Epsom salt taken orally will act mainly as a laxative rather than a magnesium supplement.
- For constipation relief: Epsom salt’s poor absorption is actually an advantage here. Its osmotic effect in the intestines makes it an effective short-term laxative.
- For topical muscle soreness: Applying magnesium chloride to the skin (as a spray or gel) may help relieve localized muscle soreness, though current evidence suggests it won’t significantly raise your overall magnesium levels.
Price and Availability
Epsom salt is one of the most affordable magnesium products available. You can find it at virtually any pharmacy or grocery store, often for a few dollars per bag. Because most of it is synthetically produced at scale, the price stays low.
Magnesium chloride flakes typically cost more, sometimes two to three times as much per pound. Products sourced from specific deposits like the Zechstein seabed carry a further premium. Whether that extra cost is worth it depends on your intended use. For a relaxing bath, the price difference is hard to justify based on current science. For oral supplementation, magnesium chloride’s better absorption makes it the more effective option regardless of price.