How to use Epsom salt in the bath
An Epsom salt bath is a warm bath with Epsom salt (magnesium sulfate) dissolved into the water. Follow the amount on the pack, keep the water warm rather than hot, and soak for 15 to 20 minutes. It takes its name from a spring at Epsom in Surrey that became famous in the 1600s, and many people use it as part of an end-of-day ritual.
Quick answer
- What it is: Epsom salt is magnesium sulfate, a mineral salt named after the town of Epsom in Surrey.
- How much: follow the directions on the pack. UK packs typically suggest somewhere between about 100 and 500 g for a full bath.
- Water temperature: warm, not hot, close to body temperature.
- How long: 15 to 20 minutes.
- How often: once or twice a week suits most people.
- Check with your doctor first if you are pregnant, have diabetes, have kidney problems, or have broken or irritated skin.
What is Epsom salt?
Epsom salt is magnesium sulfate, a mineral compound made of magnesium, sulfur and oxygen. The kind sold for baths is usually magnesium sulfate heptahydrate, which means each unit of the salt holds seven molecules of water in its crystals (chemical formula MgSO₄·7H₂O).
It looks like coarse, clear-to-white crystals, a little like table salt, but it is a different compound. Table salt is sodium chloride; Epsom salt contains no sodium chloride at all. Our guide to choosing bath salts compares it with Dead Sea, sea and Himalayan salt.
Why is it called Epsom salt?
Epsom salt is named after Epsom, a town in Surrey, England, where a bitter-tasting spring was found on the common around the turn of the 1600s. Salt was later produced by evaporating the spring water, and the name "Epsom salt" was in use by the end of the 1600s. Epsom became a well-known spa town.
How much Epsom salt should you put in a bath?
Follow the directions on the pack you buy. There is no single official amount, and packs vary: UK pack directions typically suggest somewhere between about 100 and 500 g for a full bath, and less for a half-filled one.
Start at the lower end. Adding more does not change much other than how the water feels.
How do you run an Epsom salt bath?
To run an Epsom salt bath, dissolve the salt in warm running water, then soak for 15 to 20 minutes.
- Run the bath warm, not hot. Very hot water can leave skin feeling dry and can make you feel light-headed.
- Add the Epsom salt under the running tap so it dissolves as the bath fills. Swirl the water with your hand to dissolve any crystals left on the bottom.
- Get in once the salt has fully dissolved.
- Soak for 15 to 20 minutes.
- Rinse with clean water if you like, pat dry, and follow with a moisturiser if your skin tends to feel dry.
Many people find Epsom salt makes the water feel softer. Keep a glass of water nearby, and don't bathe when drowsy or after drinking alcohol.
What temperature should an Epsom salt bath be?
An Epsom salt bath should be warm, not hot: close to body temperature (pack directions typically say about 37°C) is comfortable for most people. If you don't have a bath thermometer, the water should feel pleasantly warm on the inside of your wrist, never uncomfortably hot. For children, use cooler water and always supervise.
How long should you soak in an Epsom salt bath?
Soak in an Epsom salt bath for 15 to 20 minutes. That is long enough to settle in and enjoy the warm water, without the skin drying out or the heat becoming too much. Longer soaks are not needed. For more on timing and temperature, see how long to soak in the bath.
How often can you have an Epsom salt bath?
Once or twice a week suits most people. If your skin feels dry or tight afterwards, space your baths further apart and moisturise after each one.
Does your skin absorb magnesium from an Epsom salt bath?
The evidence that skin absorbs a meaningful amount of magnesium from bath water is limited and unproven. A 2017 scientific review of transdermal magnesium (magnesium taken in through the skin) concluded that the research so far does not support it. An Epsom salt bath is simply a warm, mineral-salt soak: the salt dissolves into the water and changes how the water feels. Our guide to the magnesium bath looks at the research in more detail.
Who should check with a doctor before an Epsom salt bath?
Check with your doctor before an Epsom salt bath if any of the following apply to you:
- you are pregnant
- you have diabetes
- you have kidney problems
- you have broken, cut or irritated skin
- you have a heart condition or low blood pressure, or feel faint in hot water
- you are unsure for any other reason
Epsom salt for the bath is for external use only. Never drink bath salts.
Epsom salt in SLATE
Every SLATE block is a pressed bath block of around 22 g, and every block contains 10% Epsom salt (magnesium sulfate). The SALT block is Epsom salt on its own. Each block fizzes as it dissolves, from bicarbonate and citric acid.
To be clear about amounts: a SLATE bath contains some Epsom salt, but far less than a traditional Epsom salt bath. Even a full Grid™ of 27 blocks holds well under 100 g of Epsom salt, compared with the 100 to 500 g that pack directions typically suggest on its own. If you want a traditional Epsom salt bath, add plain Epsom salt alongside your blocks. The System explains how the blocks combine in a Grid™.
A Grid™ for an end-of-day soak
9 CALM · Lavender and chamomile · Quiet the noise
9 OAT · Colloidal oat · Calm and soften
6 SOFT · Peach and magnolia · Be gentle
3 CLAY · Kaolin clay
Build this Grid™ →
Common questions
Is Epsom salt the same as magnesium sulfate?
Yes. Epsom salt is the common name for magnesium sulfate, usually in its hydrated crystal form (MgSO₄·7H₂O).
Is Epsom salt the same as table salt?
No. Table salt is sodium chloride; Epsom salt is magnesium sulfate, a different mineral compound.
How much Epsom salt do I need for a bath?
Follow the directions on your pack; UK packs typically suggest about 100 to 500 g for a full bath. Start at the lower end.
How long should I stay in an Epsom salt bath?
15 to 20 minutes, in warm rather than hot water.
Can I use Epsom salt with other bath products?
Yes, in most cases. Dissolve the Epsom salt first, then add your other products, and patch-test anything new.
Should I rinse off after an Epsom salt bath?
A quick rinse with clean water is fine if your skin feels dry afterwards. Many people simply pat dry.
Can I have an Epsom salt bath when pregnant?
Check with your doctor or midwife first, and keep the water warm, not hot.
Sources
- Epsom Salts, University of Waterloo, Wat on Earth
- Myth or Reality—Transdermal Magnesium?, Gröber, Werner, Vormann and Kisters, Nutrients, 2017
- Fainting, 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™
