Black spots in the grout, dark patches on silicone around the bath, speckles on the ceiling above the shower — bathroom mould is one of the most common problems we see in homes and rentals across Surrey, Sussex and South London. It looks unpleasant, it can be difficult to remove, and it tends to come back if the underlying cause isn’t dealt with.
This guide explains why it happens, how to clean it, and how to keep it away.
Why mould grows in bathrooms
Mould needs moisture, a surface to grow on and something to feed on. Bathrooms offer all three: steam from showers and baths, porous grout and sealant, and soap residue and skin cells to feed on.
The biggest factor is condensation. When warm, moist air hits cold surfaces — tiles, windows, ceilings, outside walls — it turns back into water. If that moisture has nowhere to go, surfaces stay damp and mould takes hold.
Where it usually appears
- Grout lines, especially low down and in corners
- Silicone sealant around baths, showers and basins
- Ceilings above showers
- Window frames and sills
- Behind shower curtains and on the curtain itself
- Around extractor fans that aren’t working properly
How to clean light surface mould
For small patches of surface mould on tiles and grout:
- Open a window and put on rubber gloves
- Use a mould and mildew spray designed for bathrooms and follow the instructions on the label
- Leave it for the recommended time so it can work
- Scrub gently with a soft brush or old toothbrush
- Rinse and dry the area thoroughly
Why some mould won’t come out
Surface mould on tiles usually cleans off well. But when mould has grown into porous grout or behind silicone sealant, cleaning may lighten it without fully removing the staining. In those cases, the long-term fix is often to rake out and replace the affected grout or reseal the bath or shower — a maintenance job rather than a cleaning one.
We’ll always be honest about what cleaning can realistically achieve before we start.
Condensation or something else?
A quick way to tell whether bathroom mould is caused by everyday condensation or a bigger issue:
- Likely condensation: mould appears on cold surfaces (windows, outside walls, ceilings above showers), worse in winter, and improves when ventilation improves
- Possibly a leak or damp issue: patches that stay wet, spread quickly, appear on internal walls, come with staining or tide marks, or smell strongly musty
If you suspect a leak or rising damp, get it looked at before spending money on cleaning — otherwise the mould will simply return.
When it’s more than a cleaning problem
Widespread mould, mould on walls away from the bathroom, damp patches, peeling paint or a musty smell throughout the home can point to a wider damp, ventilation or leak issue. If you rent, report it to your landlord or letting agent in writing. If you own the property, it may be worth speaking to a damp or ventilation specialist. Cleaning alone won’t fix the cause.
How to stop mould coming back
- Ventilate — run the extractor fan during and for 15–20 minutes after showering, or open a window
- Check the extractor fan works — hold a sheet of toilet paper near it; if it doesn’t pull, it may need cleaning or repair
- Squeegee and dry — wipe down shower screens and tiles after use
- Keep the door open after showering (if the rest of the house is warm) so moisture can disperse
- Wash shower curtains and bath mats regularly
- Keep the room warm — cold surfaces attract condensation
- Clean little and often — tackling spots early stops them spreading
Mould at the end of a tenancy
Mould in bathrooms is often noted at check-out inspections. Surface mould that could have been cleaned may be treated as a cleaning issue, while mould caused by building defects or poor ventilation is a different matter. Cleaning what can be cleaned — and taking photos — puts you in the best position. Read more in our guide to getting your deposit back.
How we can help
Every Nestro deep clean and end of tenancy clean includes a full bathroom clean: descaling screens, tiles, taps and showerheads, scrubbing grout and sealant, and treating surface mould. If a bathroom is in a particularly bad state, we can deep clean it on its own — send us a photo and we’ll give you a custom quote.
Quick answers
Will bleach get rid of mould permanently?
Cleaning products can remove surface mould, but they don’t stop it returning. Controlling moisture with ventilation is what keeps it away.
Is black mould in the bathroom dangerous?
Mould can affect health, particularly for people with allergies, asthma or weakened immune systems. If you’re concerned, speak to a health professional, and deal with the source of the damp.
Can you remove mould from silicone sealant?
We can clean surface mould from sealant, but where mould has grown into or behind it, resealing is often the only permanent fix.