Bath soak vs bath salts vs bath bomb: what's the difference?
A bath soak is any product you dissolve into bath water to soak in: powders, salts, milks and oils all count. Bath salts are mineral salts that dissolve quietly, a bath bomb is a pressed mix of bicarbonate of soda and citric acid that fizzes, and a bath melt is a solid of butters and oils that melts into the water.
Quick answer
- A bath soak is the umbrella term for anything you dissolve or disperse in bath water to soak in: salts, powders, milks and oils all count.
- Bath salts are mineral salts that dissolve quietly and usually leave the water clear.
- A bath bomb is pressed bicarbonate of soda and citric acid, which fizzes as the two react in water.
- A bath melt is a solid of butters and oils that melts into a silky, slightly oily layer.
At a glance
| Format | What it is | What it does in the water | Residue |
|---|---|---|---|
| Bath soak | An umbrella term for anything you add to the bath to soak in | Depends on the format: it might dissolve, fizz, cloud or melt | Depends on the ingredients |
| Bath salts | Mineral salts such as Epsom salt, Dead Sea salt or sea salt | Dissolve without fizzing, usually leaving the water clear and feeling softer | Very little |
| Bath bomb | Bicarbonate of soda and citric acid pressed into a solid shape | Fizzes as the two react, often releasing colour and scent, then settles into calm, scented water | Sometimes, if it contains colour, glitter or oils |
| Bath melt | A solid of cosmetic butters and oils, such as shea or cocoa butter | Melts slowly into a thin layer of oil on the surface; the water feels silky | Yes, an oily film on skin and the bath |
What is a bath soak?
A bath soak is a general name for any product you dissolve or disperse in bath water and then lie in. The term covers bath salts, bath powders, milk and oat powders, bath oils, melts and fizzing formats. On a label, "bath soak" often means a loose blend of salts, powders and scent, sold by weight and scooped into the water.
What sets a soak apart from a shower product is time. You stay in the water for 15 to 20 minutes, so whatever is dissolved in it surrounds the whole body at once.
What are bath salts?
Bath salts are crystals of mineral salt that dissolve in warm water. The three you'll see most often are:
- Epsom salt: magnesium sulfate, a white crystal named after the spring at Epsom in Surrey where it was first found.
- Dead Sea salt: salt harvested from the Dead Sea, made up of a mix of mineral salts rather than just sodium chloride.
- Sea salt: evaporated seawater, mostly sodium chloride.
In the water, bath salts dissolve without fizzing and usually leave it clear. The water can feel softer, and there's little left behind to rinse away. For a closer look at each type, see how to choose bath salts.
What is a bath bomb?
A bath bomb is a pressed solid made mainly of bicarbonate of soda (sodium bicarbonate, an alkali) and citric acid. Dry, the two sit side by side without reacting. In water they dissolve and react, releasing carbon dioxide gas, which is the fizz. Most bath bombs also contain scent, colour and sometimes oils or butters.
In the water, a bath bomb fizzes for a minute or two, spreads colour and scent, then settles into calm water.
What is a bath melt?
A bath melt is a solid made of cosmetic butters and oils that softens and melts in warm water. Common bases are shea butter and cocoa butter. A melt doesn't fizz or dissolve; it forms a thin layer of oil on the water's surface.
The water feels silky and skin feels smooth afterwards. Because it's oil, a melt leaves the bath slippery, so take care getting in and out and give the tub a wipe once you're done.
What's the difference between bath salts and a bath bomb?
The main difference is the fizz: bath salts dissolve quietly, while a bath bomb fizzes because bicarbonate and citric acid react in the water. Bath salts usually leave the water clear and the bath clean. A bath bomb is more about the moment, with movement, colour and scent as it dissolves. Many people simply choose by mood: still and simple, or lively and colourful.
How to use a bath soak
Every format follows the same basic steps.
- Run the bath warm, not hot. Very hot water can leave skin feeling dry.
- Add the product once the bath is full or nearly full. Salts and powders disperse more evenly; a fizzing product keeps its fizz for when you're in.
- For salts, swirl the water until the crystals dissolve. For a melt, drop it in and let it soften.
- Soak for 15 to 20 minutes.
- Rinse with clean water and pat dry. After a melt, wipe the bath so it isn't slippery for the next person.
How to choose between them
Choose by how you want the water to look and feel.
- Clear water, nothing to clean up: bath salts.
- Fizz, colour and scent: a bath bomb.
- Silky water and smooth-feeling skin: a bath melt.
- Soft, milky water: an oat or milk powder soak, such as an oat milk bath.
- A mix of all of these: combine formats in one bath.
If your skin is sensitive, start with a simple, unfragranced format and patch-test anything new.
Where SLATE fits
SLATE blocks are small pressed bath blocks, about 22 g and 2.5 cm across, that fizz as they dissolve. Every block has a base of Epsom salt (10%) and kaolin clay, a soft white clay, plus its own ingredient and scent.
Instead of one product per bath, you build a Grid™ of up to 27 blocks. That means a single bath can combine salt, clay, oat and scent. The System explains how it works.
- SALT: Epsom salt
- CLAY: kaolin clay
- OAT: colloidal oat. Calm and soften
- CALM: lavender and chamomile. Quiet the noise
- SOFT: peach and magnolia. Be gentle
- FOAM: extra foaming
A Grid™ for a bit of everything
6 SALT · Epsom salt
6 CLAY · Kaolin clay
6 OAT · Colloidal oat · Calm and soften
6 CALM · Lavender and chamomile · Quiet the noise
3 FOAM · Extra foaming
Build this Grid™ →
Common questions
What is a bath soak?
A bath soak is any product you dissolve or disperse in bath water to soak in, including salts, powders, milks and oils. The word is an umbrella term rather than one specific format.
Is a bath soak the same as bath salts?
Not always. Bath salts are one type of bath soak; a soak can also include powders, oat, milk, clay or oils.
Do bath salts fizz?
No. Plain bath salts dissolve quietly. Fizz comes from bicarbonate of soda and citric acid reacting in water, which is how a bath bomb works.
What is a bath melt?
A bath melt is a solid of cosmetic butters and oils that melts in warm water, leaving it silky. It makes the bath slippery, so take care getting out.
How long should you soak in the bath?
15 to 20 minutes in warm, not hot, water is plenty.
Can you use bath salts and a bath bomb together?
Yes. The formats can share one bath; add salts first so they dissolve, then the fizzing product.
Sources
- Bath Bomb Chemistry, American Association of Chemistry Teachers
- Epsom Salts, University of Waterloo, Wat on Earth
- Dermatologists' top tips for dry skin, American Academy of Dermatology
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™
