Mould can be encouraged by opening the bathroom window (Image: FreshSplash via Getty Images)
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, especially when the outdoor air is colder than indoors, allows the cold outside air to mix with the warm, moist air from the bathroom.
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Mould spores can grow if it is not wiped off walls and tiles (Image: Getty)
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, reports Mirror.
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%, particularly 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 having 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.”
Opening the window can do more harm than good (Image: Getty)
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 soggy, damp environment.
Keeping the floor temperature above the dew point helps prevent condensation.
Wipe down surfaces after use
After a hot shower, moisture clings to walls, mirrors, windows, and even ceilings. If neglected, this dampness can foster 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 your shower starts and leave it running for at least 30 minutes after you finish. It’s also vital to clean the fan every few months to eliminate dust and lint build-up.
Use moisture absorbers
Moisture absorbers such as silica gel, calcium chloride crystals, or desiccant containers passively absorb excess humidity from the air. They’re particularly useful in smaller bathrooms without windows or with insufficient ventilation.
This comes as UK households have been issued a black mould warning as experts urge people to carry out one “vital” test that could reveal a hidden health threat in the bathroom.
The warning comes from home heating specialists at Air To Heat, who say black mould isn’t just something that leaves dark stains on tiles and grout, it also releases invisible spores that spread through the air and can cause serious breathing problems.
Bathrooms are among the most vulnerable places in the home because they combine heat, damp, and poor ventilation. Steam from hot showers raises humidity, and when windows are shut or extractor fans aren’t used, the conditions are perfect for mould to grow.
Air To Heat said people may not even realise there’s a problem because mould spores can’t be seen. But once they’re inhaled, they can irritate the lungs and trigger coughing, sneezing, or more serious health issues in vulnerable groups.
To help identify whether spores are present in the air, the experts are urging households to try a simple home test that’s gaining attention on social media.
A viral video on TikTok has shown how placing a petri dish in the bathroom for several hours can reveal whether airborne mould is present. After it’s sealed and kept in a warm, dark place for a few hours or days, any spores in the air will settle and begin to grow.