Sea salt and Epsom salt are not the same thing. They are entirely different chemical compounds with different mineral content, different uses, and different effects on your body. Sea salt is primarily sodium chloride, the same substance as table salt. Epsom salt is magnesium sulfate, a compound made of magnesium, sulfur, and oxygen that contains no sodium chloride at all.
Despite both being called “salt” and both dissolving in water, they are about as similar as baking soda and sugar. The confusion is understandable since both show up in bath products and wellness aisles, but swapping one for the other can range from ineffective to unsafe depending on what you’re using them for.
The Chemical Difference
Sea salt is harvested by evaporating seawater. What’s left behind is mostly sodium chloride, with small amounts of trace minerals like potassium, calcium, and magnesium that give different sea salts their distinctive colors and flavors. It tastes salty because it is, chemically, the same salt you’d find in a shaker on your table.
Epsom salt looks like coarse white crystals, but it has a bitter, unpleasant taste. Its chemical name is magnesium sulfate heptahydrate, meaning each crystal holds seven water molecules within its structure. It’s typically sourced from dry lake beds, natural mineral deposits, or produced industrially by reacting magnesium-containing minerals with sulfuric acid. Some production methods extract it from bittern, the liquid left over after salt is harvested from seawater, but the end product is a completely different compound from the sea salt that came out first.
Can You Eat Epsom Salt?
Sea salt is a food product. You cook with it, season with it, and your body needs the sodium it provides (in moderate amounts) to function. Epsom salt is not a food ingredient and should not be used in cooking. While pharmaceutical-grade magnesium sulfate exists and has been used medicinally as a laxative, the Epsom salt sold for baths is intended for external use only. The packaging matters here: never substitute one for the other in recipes, and don’t assume that a product sold for soaking is safe to swallow.
Different Benefits in the Bath
Both salts are popular for baths, but they work in different ways because they deliver different minerals to your skin.
Epsom salt baths are most commonly used for muscle soreness and post-workout recovery. The idea is that magnesium absorbs through the skin during a soak, helping to ease tension and reduce minor aches. Research from the University of Queensland has confirmed that magnesium ions can penetrate through intact skin, with hair follicles playing a significant role in absorption. At higher concentrations, measurable amounts of magnesium permeate into the outer skin layers after about 15 minutes of exposure. This gives some scientific support to the long-standing practice of soaking in Epsom salt after physical strain, though the amount absorbed is modest compared to taking magnesium orally.
Sea salt baths, particularly those using mineral-rich varieties like Dead Sea salt, tend to be better for skin concerns. The high magnesium and zinc content in mineral-rich sea salts can help strengthen your skin’s moisture barrier, and people dealing with dryness, flakiness, or irritation often find relief from soaking in them. Coarser sea salts also work well as physical exfoliants for rough patches when used as a scrub before soaking.
How to Choose the Right One
Your choice depends entirely on what you’re trying to accomplish:
- Sore muscles after exercise: Epsom salt. Its magnesium content is the active ingredient, and muscle recovery is its primary use case.
- Dry, irritated, or flaky skin: Mineral-rich sea salt, especially Dead Sea salt, which delivers a broader range of skin-supporting minerals.
- General relaxation: Either will work. Warm water does most of the relaxing on its own, and both salts add a mineral component that many people find soothing.
- Cooking: Sea salt only. Epsom salt has no place in food preparation.
Why the Name “Salt” Is Misleading
In chemistry, a “salt” is any compound formed when an acid reacts with a base. Sodium chloride is one salt. Magnesium sulfate is another. Potassium nitrate (saltpeter) is yet another. They’re all “salts” in the chemical sense, but they have wildly different properties, tastes, and biological effects. The word “salt” in everyday language has become so tied to sodium chloride that calling anything else a salt creates confusion.
Epsom salt gets its name from Epsom, a town in Surrey, England, where the compound was first distilled from natural springs in the 17th century. The locals noticed the water tasted bitter and had different properties from ordinary salt water. They were right: it was an entirely different mineral dissolved in the groundwater, and the two have nothing in common beyond their crystalline appearance and ability to dissolve in a warm bath.