People warned not to open bathroom window after shower

It’s a common practice to open a window after a shower to let out the steamy, humid air. Many homeowners might think it’s a simple and effective way to prevent  mould growth in the most vulnerable room.

However, experts have cautioned that this daily routine needs to stop as it could actually be encouraging mould growth in the bathroom rather than preventing it. In many cases, it could be the reason you’re noticing patches of the black fungus in your smallest room. Specialists at Shutter Store explain that opening the window after a shower, particularly when the outdoor air is colder than indoors, allows the cold outside air to mix with the warm, moist air from the bathroom.

This results in water vapour condensing quickly on surfaces, creating the perfect conditions for mould to flourish.

The World Health Organisation (WHO) identifies persistent dampness as the main factor in mould development, making the bathroom the ideal habitat.

It’s estimated that the likelihood of finding mould in a bathroom is two to three times higher than in bedrooms or living rooms.

After a hot shower, humidity levels in a bathroom can increase by up to 90%, especially in small or poorly ventilated spaces. This moisture sticks to tiles, mirrors, ceilings, and windows, and if not properly managed, mould can start to grow within 24 to 48 hours.

Throwing open a window after a shower might seem helpful, but it can actually interfere with the airflow created by extractor fans and introduce cold air that accelerates condensation build-up. This leads to extra moisture gathering on surfaces, exactly what mould needs to thrive.

Sam Tamlyn, Managing Director at Shutter Store, said: “Opening the bathroom window after a shower can reduce the effectiveness of your extractor fan and create cross-drafts that spread moisture. Instead, focus on wiping down surfaces and letting your fan do its job. Understanding how ventilation works is key to keeping mould at bay.”

Experts recommend the following mould-prevention methods instead that don’t require opening the window:

Apply shaving foam on mirrors

By smearing a small amount of shaving foam onto the mirror’s surface and wiping it with a towel or microfibre cloth, a barrier is created between the steam and the glass. This method can keep your mirror steam-free for several weeks.

Underfloor heating

Cold surfaces such as ceramic or stone tiles draw condensation like magnets. When warm, moist air meets these chilly surfaces, it turns into water droplets, creating a wet, damp environment.

Keeping the floor temperature above the dew point helps prevent condensation.

Wipe down surfaces after use

After a hot shower, moisture sticks to walls, mirrors, windows, and even ceilings. If not dealt with, this dampness can lead to mould growth. To avoid this, use a towel or squeegee to wipe down tiles, glass, and countertops. Pay special attention to corners and grout lines, where mould tends to gather.

Turn on the extractor fan

Extractor fans are designed to remove humid air from the bathroom and vent it outside.

Switch on the fan before you start your shower and leave it running for at least 30 minutes after you finish. It’s also vital to clean the fan every few months to get rid of dust and lint build-up.

Use moisture absorbers

Moisture absorbers like silica gel, calcium chloride crystals, or desiccant containers are passive devices that soak up excess humidity from the air. They’re particularly useful in smaller bathrooms without windows or with poor ventilation.