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    Ingredient guide · Ingredient reference

    Epsom salt is magnesium sulfate heptahydrate

    Epsom salt names a particular hydrated form of magnesium sulfate. It is not another name for every magnesium salt or for magnesium chloride.

    Read the evidence ↓

    Supplement Science Insights Editorial Team

    Published September 23, 2026

    What the source establishes

    The International Chemical Safety Card for magnesium sulfate identifies the heptahydrate as Epsom salt. It separately lists several other hydration states and their registry numbers. [1]

    The same card presents the formula and physical properties of magnesium sulfate. Its notes distinguish the heptahydrate, so a number printed for the base compound should not automatically be assigned to every hydrated form. [1]

    What it does not establish

    Hydration-state identity does not establish an appropriate route or purpose for a finished product. Bath products and medicinal preparations require their own directions and specifications. Shared magnesium content does not make sulfate and chloride interchangeable ingredients. [1]

    A hypothetical distinction

    Imagine a calculation uses the mass of a water-free compound for a hydrated crystal. The included water changes the relationship between material mass and constituent amount.

    Key distinctions — Epsom salt is magnesium sulfate heptahydrate
    DetailInterpretation
    HeptahydrateSpecific hydrated form
    Magnesium chlorideDifferent salt
    Product useRead its own directions
    Epsom salt is magnesium sulfate heptahydrate — original article outline diagram
    Original editorial diagram of this article’s sections; no product photograph or clinical finding is depicted.

    Sources for this article

    1. ICSC 1197 - MAGNESIUM SULFATE
      Source consulted: 2026-09-19. This is a reference resource, not a claim that we conducted the studies or tested a product.