Mould on your bathroom ceiling? Start with the fan

Mould on a bathroom ceiling is almost always caused by steam with nowhere to go. A hot shower puts a lot of water into the air, and if that moisture doesn't clear quickly it condenses on the coldest surface in the room, which is often the ceiling. Get the airflow right and the mould has far less to feed on.

Why it grows up there

Warm, wet air rises, so the ceiling gets the first hit. It's also one of the coldest surfaces in a bathroom, especially in a top-floor flat with a cold loft above or a ceiling with little insulation. Damp settles on it as a thin film, dust and skin cells collect there, and mould takes hold.

The usual reasons are:

• The extractor fan is missing, too weak, or switched off too soon after a shower.
• The fan vents into the loft or the ducting is blocked, sagging or disconnected, so the moist air is still in the building.
• Trickle vents or a window have been sealed up, so there's no fresh air coming in.
• The room is cold, so the ceiling stays close to the temperature where steam turns to water.

Older Scottish homes often have one of these problems, and sometimes more than one. A fan that looks like it's working can still be moving very little air.

What you can do this week

Start with the cheapest changes. Run the fan while you shower or bath, and leave it going for a while after you finish, until the mirror has cleared. Shut the door to keep the steam in the bathroom, and open a window if there is one.

To check the fan, hold a tissue or a piece of paper against the grille while it's on. If it doesn't pull the paper firmly against the grille, it's not moving enough air. That's a job for an electrician or a fan installer, and it's often the fix that stops the mould coming back.

Wipe the ceiling and the walls around the bath or shower after use if you can. Small patches can usually be cleaned with a mould-killing spray and a damp cloth, then dried. Ventilate while you clean, and don't scrub hard enough to spray the mould around. Don't paint over it until it's dry and you know the cause is sorted, because it will come through the paint. If the mould is on the grout or silicone round the shower itself, see our guide to mould in the shower.

When it's more than condensation

Condensation mould tends to sit in patches near the bath, the shower or the fan, and it comes back each winter after it's cleaned. Other causes look different, and they need a different fix:

• A stain that grows after heavy rain, or sits beside a roof, chimney or gutter, can mean water is getting in from outside.
• A stain near pipework, under a shower tray or around the bath panel suggests a leak.
• Bubbling paint, a damp smell that's worst in one spot, or a ceiling that feels soft means a leak until someone has proved otherwise.

If the stain is brown, spreads after rain, or you can see water, don't wait for the next big clean. Get someone to look at it sooner rather than later.

Your health

The NHS says mould can trigger asthma in people who are allergic to it. If you or someone at home has asthma, or a mould allergy, take the damp seriously and keep an eye on any breathing changes. The NHS asthma causes page lists mould among the things people can be allergic to. Official guidance for landlords in England, Damp and mould: understanding and addressing the health risks for rented housing providers (MHCLG, DHSC and UKHSA), adds that people with a weakened immune system are also at greater risk. If symptoms get worse, speak to your GP.

When to get a specialist

Get a damp specialist to look if the mould keeps coming back after you've improved the fan and the airflow, if the patch covers more than a small area, or if you think there's a leak or a roof problem. Tell us what's happening and we'll pass it to one independent specialist who covers your area. It's free to ask, and they quote you directly.

Last checked 26 October 2026. This is general guidance, not legal or building advice.