What is mould?
Mould is a type of fungus that grows when its microscopic spores settle on damp surfaces. These spores are like single-celled seeds that are always present in the air, but they only develop into visible mould when three things come together: moisture, warmth, and organic material such as wood, paper, or dust.
As part of the Fungi kingdom, mould is genetically closer to humans than to plants, and in nature, mould serves to recycle organic material such as leaves and wood, returning nutrients to the soil. And while mould is to thank for penicilin, soy sauce, and blue cheese, mould growing indoors damages materials and can affect your health if not controlled.
What causes mould?
Mould is mainly caused by excess moisture and poor airflow. Mould starts when microscopic spores — which are always present in the air — find a damp surface to settle on. On their own, spores float around harmlessly. But if excess moisture builds up and there’s little airflow, they can settle and grow into the black, green, or white patches you see on walls, ceilings, or furniture.
The most common trigger inside UK homes is condensation: everyday activities like cooking, showering, and even breathing release moisture into the air. If the air isn't able to hold all that extra moisture (or airflow isn't enough), it will drop the moisture onto cold surfaces (this is condensation), creating the perfect environment for mould to develop.
Is mould bad for my health?
Yes — mould can release spores and particles into the air that, when breathed in, may irritate your lungs and airways. For some people this causes mild symptoms like coughing, sore throat, or headaches. For others — especially children, older adults, or people with asthma — it can trigger allergic reactions and more serious breathing difficulties.
Not every mould species is equally harmful, but any visible mould indoors should be treated as a warning sign. Preventing damp and improving ventilation is the safest way to reduce the health risks linked to mould.
How can I prevent mould in my home?
Surface cleaning with bleach or sprays can remove visible mould patches, but it doesn’t stop them from coming back. That’s because the real cause is excess moisture combined with poor airflow.
To reduce your risk of mould:
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Wipe away condensation from windows and sills.
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Use lids when cooking and extractor fans in kitchens and bathrooms.
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Avoid drying clothes indoors where possible.
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Leave a small gap between furniture and external walls so air can circulate.
These steps can help day to day, but the only long-term way to prevent mould is to tackle condensation and improve ventilation. Our free survey can identify the right ventilation system to keep moisture under control across your whole home.
Why does mould keep coming back after cleaning?
Cleaning mould with bleach or sprays only removes what you can see on the surface. The spores that cause mould are always present in the air, and if excess moisture and poor airflow remain, those spores will simply settle and grow again.
That’s why mould often seems to “come back” after a few days or weeks — the underlying conditions haven’t changed. To stop mould returning, you need to control condensation and improve ventilation so damp air doesn’t settle on cold surfaces.
How does ventilation help reduce mould?
Ventilation helps by tackling the root cause of mould — excess moisture trapped in still air. By moving damp air out and bringing drier air in, ventilation stops condensation from settling on cold surfaces where mould can grow.
Extractor fans are effective in kitchens and bathrooms where most moisture is produced. For whole-home protection, continuous systems keep air circulating throughout the property, helping to prevent condensation and reduce the conditions that mould needs to thrive.
