Not vinegar, not bleach: this forgotten bathroom ingredient dissolves pink mould in minutes

Lynne Lart • December 08, 2025 16:14

Not vinegar, not bleach: this forgotten bathroom ingredient dissolves pink mould in minutes

Between rushed showers and steamy evenings, a pink film quietly settles on grout lines, around taps and at the base of the shower curtain. Many people try vinegar, others reach for bleach, and both are often disappointed: the colour comes back, sometimes within days. Yet at the back of many cleaning cupboards sits a simple powder that does a better job with far less scrubbing: borax.

Borax has fallen out of fashion as spray bottles have taken over supermarket aisles. It is rarely on the front of the shelf, almost never in TV adverts, and often mislabelled in people’s minds as “old-fashioned” or “too strong”. In practice, it is a stable mineral salt that, when handled correctly, attacks the very structure of pink mould and the biofilm that protects it.

The effectiveness of borax comes from its ability to disrupt the slimy layer that shelters pink mould, rather than only bleaching the colour on the surface.

What is the “pink mould” in your bathroom really?

The pink stains along your silicone seal or under the shampoo bottles are usually not a true mould, but a bacterium: most often Serratia marcescens. It thrives in damp, slightly soapy environments, feeding on soap scum and organic residues. The result is a slippery, sometimes stringy film that clings to tiles, curtains and plastic trays.

Bleach can whiten that film and vinegar can dull it, but both often leave parts of the biofilm intact. Under the right conditions-warmth, moisture, a bit of shampoo-pink patches reappear from what was left behind. That is why a surface can look clean on Monday and show a faint blush of pink again by Friday.

Fighting this organism effectively means dealing with three things at once: the bacteria themselves, the protective film that shelters them, and the underlying grime they feed on. Borax acts on all three.

Why borax works where bleach and vinegar falter

Borax (sodium borate) dissolves in warm water to create a mildly alkaline solution with gentle abrasive properties when still in powder form. This combination helps to break down soap scum, soften mineral deposits and destabilise the slime layer that hides the bacteria. Instead of just lightening the stain, it makes the surface less hospitable in the first place.

Where bleach offers a dramatic but often superficial whitening, borax focuses more on detaching the film from the surface. Vinegar, meanwhile, is acidic; it helps against limescale but can be less effective on the fatty residues left by shampoos, conditioners and body washes. In a bathroom, those residues are what pink mould feeds on most consistently.

Used correctly, borax becomes a kind of “reset button” for grout and sealant. It cleans, deodorises and, crucially, makes it harder for the film to get a new grip. That translates into fewer cleanings and less aggressive scrubbing over time.

How to use borax on pink mould, step by step

The method is simple and does not require special tools. A bowl, a sponge and a pair of gloves are usually enough.

Preparing a borax paste or solution

Dry the area first. Wipe excess water from tiles, sealant and shower trays so the product is not instantly diluted.
Mix a paste: combine roughly 2–3 tablespoons of borax with a little warm water until it forms a thick, spreadable paste.
For larger, less stubborn areas, prepare a solution instead: 1 tablespoon of borax per 250 ml of hot (not boiling) water in a spray bottle or bowl, stirred until fully dissolved.

Applying it to problem spots

Spread the paste directly onto the pink mould, pressing it lightly into grout lines and along silicone edges. For vertical surfaces, a slightly thicker paste helps it stay in place. On shower curtains or removable items, you can soak them in the borax solution in a bucket or bath for better coverage.

Let the product sit for at least 15–20 minutes. In cases of heavy build-up, 30 minutes is reasonable. During this time, the borax works into the film and loosens the bond between the bacteria, the slime and the surface.

Rinsing and finishing

After the contact time, use a soft brush or non-scratch sponge to agitate the paste. Many pink patches will slide off with surprisingly little force. Rinse thoroughly with warm water, checking crevices and the base of fixtures where residue can hide.

If a faint stain remains, a second, shorter treatment is often enough. It is better to repeat a gentle cycle than to attack silicone or grout with hard tools that can damage them and create new hiding places for moisture and microbes.

Safety, surfaces and where not to use it

Like any cleaning product, borax deserves a few precautions. It is not a toy, but it is manageable with basic common sense.

Handling guidelines

Wear household gloves to avoid dryness or irritation on sensitive skin.
Avoid inhaling fine dust: scoop rather than pour vigorously, and mix close to the bowl.
Keep the box out of reach of children and pets, as you would with washing powder or bleach tablets.

Suitable and unsuitable surfaces

Borax works well on:

Ceramic tiles and standard grout.
Acrylic and fibreglass shower trays.
Porcelain sinks and toilet bases.
Most plastic accessories that can be rinsed thoroughly.

It is better avoided or tested carefully on:

Unsealed natural stone, which can react to alkaline products.
Very old, cracked grout that may need replacing rather than repeated chemical treatment.
Metal finishes with special coatings; always test a small, hidden spot first.

A simple rule of thumb: if a surface tolerates standard bathroom cleaners and mild abrasives, it generally tolerates borax. When in doubt, dilute more and shorten contact time.

Keeping pink mould from coming back

No product can out-perform a permanently damp, warm and poorly ventilated bathroom. Once the worst of the pink mould is gone, a few adjustments can extend the time between deep cleans.

Simple habits that make a difference

Ventilation after showers: open a window or run the extractor fan for at least 15 minutes to lower humidity.
Remove standing water: pull the shower curtain closed to let it dry flat, and squeegee tiles and glass where possible.
Rinse away product build-up: once or twice a week, run plain warm water over corners that collect shampoo or conditioner.

You can also keep a small bottle of diluted borax solution on hand (labelled clearly) for quick wipe-downs on problem spots. A brief spray and rinse every few days on the base of the shower or along chronic grout lines can prevent the film from ever reaching its slippery, visible stage.

Alternatives if you cannot find borax

In some regions, borax is less visible in shops or sold under different names (such as “sodium borate” or as part of multi-purpose laundry boosters). If it is genuinely unavailable or you prefer not to use it, there are partial substitutes.

Product	Main action	Limit against pink mould
Oxygen bleach (percarbonate)	Good whitening, breaks down organic stains	May need longer soaks; less effective on heavy soap scum without pre-clean
Baking soda	Mild abrasive, odour control	Often needs pairing with a detergent; slower on stubborn biofilm
Vinegar	Dissolves limescale, cuts some residues	Acidic: less suited to fat-rich soap scum on its own; colour often returns quickly

Combining a degreasing bathroom cleaner with one of these can help, but the specific mix of cleaning, deodorising and biofilm disruption is what makes borax stand out for pink mould.

FAQ:

Is borax safe to use around children and pets once rinsed? When used as directed, applied to surfaces and rinsed thoroughly, residual levels are typically low. As with any cleaner, keep the raw powder and freshly made solutions out of reach, and let surfaces dry before small children or pets have prolonged contact.

Can I use borax on coloured grout or sealant? Yes, in most cases. Because borax is not a bleach, it is less likely to strip colour, but always test a small, hidden section first to be certain your specific materials do not react.

How often should I treat pink mould with borax? For a heavy initial infestation, one or two treatments in the same week may be necessary. After that, a light application every few weeks in known trouble spots, combined with better ventilation, is usually enough.

Does borax work on black mould as well? It can help loosen and clean some darker fungal growths, but black mould may indicate deeper moisture problems in walls or seals. In such cases, structural repairs and, if needed, professional advice matter more than any surface cleaner.

Where can I usually find borax in UK shops? It is often tucked away near washing powders, stain removers or household cleaning supplies. If it is not on the shelf, online retailers and some hardware or DIY stores frequently stock it under cleaning or laundry additives.