What is a magnesium bath?
A magnesium bath is a warm bath with a magnesium salt dissolved in it, usually Epsom salt (magnesium sulfate) or magnesium flakes (magnesium chloride). It makes the water feel softer and silkier on the skin. It's a cosmetic ritual, not a supplement: the evidence that skin absorbs meaningful magnesium from bath water is limited and inconclusive.
Quick answer
- What it is: a bath with a magnesium salt dissolved in the water.
- The two kinds: magnesium sulfate (Epsom salt) and magnesium chloride (sold as magnesium flakes).
- How to run one: dissolve the salt in a warm, not hot, bath and soak for 15 to 20 minutes.
- How it feels: the water feels softer.
- Skin absorption: a 2017 scientific review found the case for absorbing magnesium through the skin is not supported by good evidence.
- In SLATE: every SLATE block contains 10% Epsom salt, about 2.2 g per 22 g block.
What is a magnesium bath?
A magnesium bath is any bath where a magnesium salt has been dissolved in the water. A salt, in chemistry, is a compound of a positively charged part (here, magnesium) and a negatively charged part (sulfate or chloride). Both dissolve easily in warm water, leaving it clear.
People run magnesium baths for the feel of the water and the ritual of a long, quiet soak. That's all this guide describes.
What is the difference between magnesium flakes and Epsom salt?
Magnesium flakes are magnesium chloride and Epsom salt is magnesium sulfate: both contain magnesium, but they are different compounds that look and feel different.
Epsom salt (magnesium sulfate)
- Chemical formula MgSO₄, usually sold as the hydrated form, MgSO₄·7H₂O.
- Looks like small clear or white crystals, a little like coarse table salt.
- Named after Epsom in Surrey, where it was first taken from spring water in the 1600s.
- Dissolves to clear water that feels soft.
Magnesium flakes (magnesium chloride)
- Chemical formula MgCl₂, usually sold as the hydrated form, MgCl₂·6H₂O.
- Looks like flat white flakes.
- Can come from ancient seabed deposits, such as the Zechstein salts under the northern Netherlands, or from the Dead Sea.
- Draws moisture from the air, so flakes can clump if left open.
Neither is "stronger" in any way that matters for a cosmetic bath. Choose by feel and preference.
Does your skin absorb magnesium from a bath?
The honest answer is that nobody has shown it convincingly. In 2017 a review in the journal Nutrients, "Myth or reality — transdermal magnesium?" by Gröber and colleagues, looked at the available research on magnesium through the skin (transdermal means "across the skin"). It concluded that promoting transdermal magnesium is not supported by the science, and that the existing studies are few, small and of limited quality.
The skin's outer layer acts as a water-repellent barrier. So a magnesium bath should not be thought of as a way to take magnesium. If you have questions about your magnesium intake, speak to your GP or a pharmacist.
How do you run a magnesium bath?
To run a magnesium bath, dissolve the salt in a warm bath and soak for 15 to 20 minutes.
- Run the bath warm, not hot. Very hot water can leave skin feeling dry.
- Add the salt as the bath fills, under the running tap, so it dissolves fully. Packs of Epsom salt or flakes usually suggest an amount on the label; follow it. Our guide to using Epsom salt in the bath covers amounts in more detail.
- Stir with your hand to check nothing is left at the bottom.
- Soak for 15 to 20 minutes. Longer soaks aren't needed.
- Rinse with clean water if you like, pat dry, and moisturise if your skin tends to feel dry.
Don't bathe when drowsy or after alcohol, and never leave children unsupervised in the bath. For more on timing and temperature, see how long to soak in the bath.
How often can you have a magnesium bath?
Once or twice a week suits most people. Think of it as a ritual you return to, not a routine you must keep. If your skin feels dry or irritated, take a break.
Who should check with a doctor before a magnesium bath?
Check with your doctor first if you are pregnant, have a skin condition, have broken or very sensitive skin, or have any ongoing health concern. Patch-test any new product, and stop if your skin reacts.
Where SLATE fits
Every SLATE block contains magnesium salt: each has 10% Epsom salt (magnesium sulfate) in its formula, and the SALT block is Epsom salt on its own. Each block is a pressed bath block of about 22 g, so that's roughly 2.2 g of Epsom salt per block.
To be clear about the numbers: a single block, or a small Grid™, contains far less magnesium salt than a traditional magnesium bath made from a bag of Epsom salt. A full 27-block Grid™ adds a little under 60 g. SLATE blocks are about scent, texture and the ritual of building a bath block by block. If you want a stronger salt soak, add plain Epsom salt alongside your blocks. The System explains how the blocks combine in a Grid™.
A Grid™ for a slow, silky soak
9 OAT · Colloidal oat · Calm and soften
9 CALM · Lavender and chamomile · Quiet the noise
9 SOFT · Peach and magnolia · Be gentle
Build this Grid™ →
Common questions
What is a magnesium bath?
A magnesium bath is a warm bath with a magnesium salt, usually Epsom salt or magnesium flakes, dissolved in it. It makes the water feel softer.
Is Epsom salt the same as magnesium flakes?
No. Epsom salt is magnesium sulfate and magnesium flakes are magnesium chloride. Both contain magnesium, but they are different compounds with a different look and feel.
Does your skin absorb magnesium from a bath?
There's no good evidence that it does in meaningful amounts. A 2017 review in Nutrients concluded that the case for transdermal magnesium is not scientifically supported.
How long should a magnesium bath be?
Soak for 15 to 20 minutes in warm, not hot, water.
Is a magnesium bath a supplement?
No. A magnesium bath is a cosmetic bath ritual. For questions about magnesium in your diet, speak to your GP or a pharmacist.
Do SLATE blocks contain magnesium?
Every SLATE block contains 10% Epsom salt (magnesium sulfate), about 2.2 g per block. SALT is Epsom salt on its own.
What is Dead Sea salt?
Dead Sea salt is a mineral salt taken from the Dead Sea, between Jordan and Israel. It contains magnesium chloride alongside other mineral salts. Our guide to choosing bath salts compares it with the other main types.
Sources
- Myth or Reality—Transdermal Magnesium?, Gröber, Werner, Vormann and Kisters, Nutrients, 2017
- Epsom Salts, University of Waterloo, Wat on Earth
- Bischofite, SaltWiki, HAWK University of Applied Sciences
- Vitamins and minerals: others, NHS
SLATE products are cosmetics for external use only. If you have a skin condition, are pregnant, or have any concerns, check with your doctor before use. Patch-test any new product. Keep out of reach of children. Contains essential oils; see each block's ingredient list for allergens. Every block contains sweet almond oil (tree nut).
SLATE is a soak for the body and mind: small-batch bath blocks of cosmetic-grade ingredients, made in the UK. Build your Grid™
