Borax is sodium tetraborate, a naturally occurring mineral salt used as a laundry booster, general cleaner, deodoriser and ant killer. It is effective and cheap — and it is toxic if swallowed, so it needs to be kept away from children and never used on food surfaces without rinsing.
What is Borax?
Borax is sodium tetraborate (also called sodium borate), a white crystalline powder. It occurs naturally as a mineral, mined from dried lake beds, and has been used domestically for well over a century.
It works in several ways at once, which is why it turns up in so many different jobs:
- It raises pH. Borax dissolves to make an alkaline solution, and alkaline conditions help break down fats, oils and grease — the same principle behind most cleaning products.
- It softens water. It binds calcium and magnesium ions, which otherwise react with detergent and reduce its effectiveness. That is why it makes ordinary washing powder work better in hard water.
- It is mildly abrasive as a powder, useful for scouring.
- It inhibits mould, fungi and some bacteria by disrupting their enzyme systems.
- It is toxic to insects, damaging their digestive systems and outer layer.
Borax and boric acid are related but not the same. Boric acid is made from borax and is more acidic; the two are often confused, and product labels are worth reading.
It is important to be clear that “natural” does not mean harmless here. Borax is a naturally occurring mineral and it is genuinely toxic if swallowed in quantity. Both things are true.
What is Borax commonly used for?
- Laundry booster — added to a wash to soften water and improve detergent performance, particularly on whites.
- Stain pre-treatment, especially on grease and protein stains.
- General cleaning — sinks, baths, tiles, worktops.
- Deodorising — bins, drains, fridges, carpets and mattresses.
- Mould and mildew control on hard surfaces, particularly bathroom grout.
- Ant and cockroach control, usually mixed with sugar as a bait.
- Slime-making, a popular craft use that carries specific cautions.
- Rust and hard-water stain removal.
- Preserving cut flowers, and drying flowers for craft.
As a laundry booster it is at its most useful in hard-water areas, where it meaningfully improves how well detergent works. It is not a detergent itself — it works alongside one rather than replacing it.
As an insecticide it is slow but effective. Ants carry the sugar-and-borax bait back to the nest, which is why it deals with a colony where a surface spray only kills what it touches. That same slowness is why the bait must be placed where children and pets cannot reach it.
How to use Borax appropriately
In practice
In the laundry: dissolve it in the water rather than tipping it onto fabric, and use it alongside your normal detergent. Test coloured or delicate fabrics first — the alkalinity can affect some dyes, and it is not suitable for wool or silk.
For cleaning: a paste of borax and a little water works on baths, sinks and tiles. Leave it a few minutes on grease or grime, then scrub and rinse thoroughly.
For mould on grout: a borax solution applied and left to dry can inhibit regrowth, since the residue continues to work.
For deodorising: sprinkle on a carpet or mattress, leave for a period, then vacuum thoroughly. Sprinkle a little in a bin before lining it.
For ants: mix with sugar and water to make a bait, and place it in a shallow container inside something a child or pet cannot open, on the ant trail rather than scattered around.
Always rinse food-contact surfaces thoroughly after using it — worktops, chopping boards, fridge interiors, lunch boxes.
Common household applications
A quick reference for where borax earns its place, and where it does not:
| Job | Works well | Notes |
|---|---|---|
| Laundry booster | Yes | Best in hard water; alongside detergent, not instead |
| Bath, sink, tile cleaning | Yes | Rinse thoroughly afterwards |
| Mould on grout | Yes | Residue keeps inhibiting regrowth |
| Deodorising bins and carpets | Yes | Vacuum thoroughly after |
| Ant and cockroach bait | Yes | Slow-acting; reaches the nest |
| Natural stone, wool, silk | No | Alkalinity damages these |
| Food itself | No | Toxic if swallowed |
Safety, surfaces and situations to avoid
Keep it locked away from children. Borax is toxic if swallowed, and the powder looks like many harmless kitchen products. If a child swallows any, contact a poison centre or go to an emergency department immediately, taking the container. Do not wait for symptoms.
Do not use it on food itself, and do not use it as a food preservative.
Wear gloves for prolonged use — it dries and irritates skin. Avoid breathing the dust, and do not use it in a poorly ventilated space.
Slime deserves specific mention, because it is the commonest way children come into contact with borax. Repeated bare-handed contact with borax slime has caused chemical burns and irritation. If slime is being made, an adult should handle the borax, children should not touch the solution directly or for long, hands should be washed afterwards, and it should never go near the mouth.
It is not suitable for:
- Wool, silk or delicate fabrics.
- Marble, granite and natural stone, which alkaline cleaners can etch or dull.
- Aluminium and some soft metals, which it can discolour.
- Painted or varnished wood, where it may damage the finish.
- Anything you will not rinse.
Do not mix it with other cleaning chemicals, particularly anything containing bleach or ammonia. Mixing household cleaners is a common cause of accidental poisoning.
Avoid it if pregnant or trying to conceive. Boron compounds have reproductive toxicity in animal studies, and several countries restrict borax in consumer products for that reason. Use an alternative.
Store it in its original labelled container, never in a food or drink container.
Seek immediate medical attention if borax is swallowed, particularly by a child; for persistent vomiting, diarrhoea or abdominal pain after exposure; for a widespread rash or skin burn; or for breathing difficulty after inhaling the dust.
Related household product guides
Frequently asked questions
What is borax used for? Boosting laundry detergent, general cleaning, deodorising, controlling mould, and killing ants and cockroaches. It is sodium tetraborate.
Is borax safe? It is safe to use with sensible precautions, but it is toxic if swallowed. Keep it locked away from children, wear gloves, and rinse food surfaces thoroughly.
Is borax the same as boric acid? No. Boric acid is made from borax and is more acidic. They are related but not interchangeable — read the label.
Can children make slime with it? An adult should handle the borax. Repeated bare-handed contact with borax slime has caused skin burns, so limit direct contact, wash hands afterwards, and keep it away from mouths.
Can I use it on granite or marble? No. Alkaline cleaners can etch or dull natural stone. Avoid it there, and on wool, silk and aluminium.
Can I use it while pregnant? Better not to. Boron compounds show reproductive toxicity in animal studies and are restricted in consumer products in some countries. Use an alternative.