Mould in the bathroom almost always has the same cause: a lot of moisture released in a short time, with nowhere for it to go except onto the coldest surfaces in the room. You can clean it off grout, silicone and ceilings, but it will come back unless the moisture is removed while you shower and for a while afterwards. Where mould keeps returning to one patch of ceiling or wall despite good extraction, it’s usually a sign of a cold spot or a leak, and that needs finding rather than repeated cleaning.
Why bathrooms get mouldy
A hot shower or bath fills the air with water vapour. When that warm, humid air meets a surface colder than its dew point (the temperature at which air can no longer hold its moisture), water condenses onto it. In a bathroom that means the window, the ceiling, the outside wall and the tiled surfaces, all of which stay damp long after you’ve dried yourself.
Mould spores are present in almost every home. Give them a surface that stays damp for hours at a time, day after day, and they grow. Bathrooms also offer plenty for mould to feed on, including soap residue, skin cells, and the porous surfaces of grout and silicone.
How to remove mould from bathroom grout
Grout is porous, so mould grows into it, not just on top of it.
- Ventilate the room and wear rubber gloves. Goggles are sensible when scrubbing overhead or with bleach-based products.
- Apply a mould remover made for bathrooms and leave it for the time stated on the label. Bleach-based products shift staining well. Never mix cleaning products, and bleach in particular must never be mixed with acidic or ammonia-based cleaners.
- Scrub with a stiff grout brush, then rinse and dry the surface.
- If staining persists, the mould has got deep into the grout. Raking out the top few millimetres and re-grouting is often quicker than repeated scrubbing.
- Seal or use a mould-resistant grout when you re-grout, and wipe tiles down after showering.
How to remove mould from bathroom silicone
Black spots in the silicone sealant around a bath or shower tray are usually in the silicone rather than on it. Surface cleaners lighten it, but the spots tend to return because the growth is embedded.
The reliable fix is to cut the old silicone out completely, clean and dry the joint thoroughly, treat it with a mould remover, let it dry fully, and re-seal with a sanitary-grade silicone that contains a fungicide. Fill the bath with water before sealing so that the joint is set at its widest when the bath is loaded, which helps it stay intact.
Failed silicone matters for more than looks. A sealant joint that has pulled away lets shower water run behind the bath or tray. That’s a common cause of hidden leaks, rotted floor joists and stained ceilings in the room below.
How to remove mould from a bathroom ceiling
- Protect yourself. Gloves, goggles and a mask, because you’ll be working overhead. Open the window.
- Don’t dry-brush it. That spreads spores. Use a fungicidal mould wash applied with a cloth or sponge, following the instructions.
- Treat a wider area than the visible spots, let the ceiling dry fully, and only then repaint, with a bathroom or anti-mould paint if you like.
Our guide on how to get rid of black mould covers safe removal in more detail. For large areas, or if anyone in the home has asthma or a weakened immune system, get help rather than doing it yourself.
Bathroom extractor fans: what the Building Regulations say
Good extraction is what actually stops bathroom mould coming back. Approved Document F, the government’s guidance on ventilation under the Building Regulations in England, sets minimum extract rates for bathrooms in new work:
| Type of extract | Minimum bathroom extract rate |
|---|---|
| Intermittent fan (runs when the room is in use) | 15 litres per second |
| Continuous extract (runs all the time, boosting when needed) | 8 litres per second (high rate) |
These figures apply to new dwellings and to work that is covered by the regulations. An existing fan in an older house doesn’t have to meet them, but they are a good benchmark, and a lot of older bathroom fans fall well short. Approved Document F applies in England. The current edition (2026) keeps the 15 l/s intermittent figure for bathrooms.
Practical points that matter as much as the number on the box:
- Check it actually extracts. A sheet of toilet paper should be held against the grille. Grilles clog with fluff, and backdraught shutters stick.
- Look at the ducting. Long, kinked or crushed flexible ducting, or a duct that just discharges into the loft instead of to the outside, can make even a powerful fan close to useless.
- Run it long enough. A fan with an overrun timer, which keeps running after the light goes off, deals with the moisture left in the air after a shower. The Energy Saving Trust suggests running fans for at least 15 minutes after bathing or showering.
- Let air in. A fan can only extract air that is replaced. A small gap under the door, or an open trickle vent, lets replacement air in.
- Bathrooms with no window. These rely entirely on the fan, so they suffer most when it fails. They are common in back-to-backs and terraces across West Yorkshire where a bathroom was carved out of a bedroom or a cellar head.
Mould on the bathroom ceiling: cold loft spot, missing insulation or a leak?
Ceiling mould that keeps coming back in one area, even with a working fan, usually has a building cause. These are the ones we see most often.
A cold spot from missing or disturbed loft insulation
If the bathroom is on the top floor, check the loft above it. Insulation that has been pulled back for wiring or plumbing, squashed by stored boxes, or never laid tight into the eaves (where the roof meets the wall) leaves a cold patch on the ceiling below. Condensation forms there first, and mould follows the cold area. The tell-tale pattern is mould along the edge of the ceiling next to the external wall, or in a neat patch matching a gap in the insulation above.
The fix is to make the insulation continuous, without blocking the ventilation gap at the eaves that keeps the roof timbers dry. Energy Saving Trust guidance on loft insulation is a good starting point.
Condensation in the extract duct
A fan duct running through a cold loft can collect condensation inside it, and that water runs back down to the fan and drips onto the ceiling. The signs are drips or staining around the fan grille. Insulated ducting, a duct laid to fall away from the fan, or a condensation trap usually cures it.
A leak
Mould or staining on the ceiling of the room below a bathroom is more often a leak than condensation. Look for a failed silicone seal, cracked grout in a shower enclosure, a leaking waste trap, or a weeping pipe joint. Staining that is brown-ringed, appears after the shower is used, and sits under the bath or shower position points firmly to a leak. A leak from the roof above a top-floor bathroom will tend to follow wet weather rather than bath time.
A cold bridge in the wall
A cold bridge is a part of the structure, such as a concrete lintel over the window, a steel beam or a gap in wall insulation, that carries cold through the wall and gives a cold stripe on the inside. Mould appearing in a line above a window or along a wall-ceiling junction often follows one. Our guide to telling condensation, penetrating and rising damp apart explains how to read the pattern.
When bathroom mould is worth an independent look
Clean it, improve the extraction, and give it a month. If it comes back to the same place, or you see any of the following, it’s worth getting the cause diagnosed:
- staining or soft plaster on the ceiling below the bathroom;
- springy or soft floor around the bath, shower or WC;
- mould in one well-defined patch that doesn’t follow the pattern of condensation;
- the extractor works, but the room still won’t dry out.
Our damp checker is a quick way to narrow down the likely cause. If you rent, damp and mould is your landlord’s responsibility to investigate and put right, and government guidance is clear that it shouldn’t be blamed on tenants’ lifestyle. Our guide to condensation on windows covers the wider picture of moisture in the home.
Getting it diagnosed
An independent damp and timber survey identifies where the moisture is coming from: condensation, a leak, a cold bridge or missing insulation. It also checks whether hidden timbers under the bath or shower have been affected. We don’t sell fans, insulation or treatments, so the recommendations are only what the building needs. Get in touch with the address and a description or photos of what you’re seeing.
Sources and further reading
- Ventilation: Approved Document F — GOV.UK
- Approved Document F, Volume 1: Dwellings (2026 edition) — GOV.UK
- How to get rid of damp — Energy Saving Trust
- Roof and loft insulation guide — Energy Saving Trust
- Damp and mould: understanding and addressing the health risks for rented housing providers — GOV.UK