Condensation mould: causes, how to tell it from damp, and how to prevent it
Updated 6 November 2026 · By the Mould Cleaning team
Short answer: Condensation mould forms when warm, moist indoor air meets cold surfaces such as window reveals, external wall corners and bathroom ceilings, and the moisture sits long enough for mould to grow. It is the most common cause of mould in UK homes and is usually fixed by better ventilation, consistent heating and reducing moisture, whereas rising or penetrating damp needs a building repair.
Condensation or damp?
| Condensation mould | Penetrating or rising damp | |
|---|---|---|
| Where it appears | Cold spots, corners, window reveals, behind furniture | Near leaks, along a tide mark or at low level on walls |
| Pattern | Scattered black spots | Patches, staining and damp plaster |
| When it is worst | Winter and cold weather | After rain or all year round |
| Usual fix | Ventilation, heating and moisture control | Repair the leak, wall or damp-proofing |
Everyday sources of moisture
- Cooking without lids or extraction
- Showers and baths without a working extractor fan
- Drying clothes on radiators or airers indoors
- Unvented tumble dryers
- Breathing overnight in closed bedrooms
- Paraffin or bottled gas heaters
How to prevent it
- Run extractor fans when cooking and showering and leave them on for a while afterwards
- Keep trickle vents open and air rooms daily
- Keep the home consistently heated rather than letting it go cold
- Leave a gap between furniture and external walls
- Wipe condensation off windows each morning
- Aim to keep indoor humidity roughly between 40 and 60 percent
If mould keeps returning despite good habits, the ventilation may be inadequate for the home or there may be a hidden damp problem, so it is worth getting it checked.
Related guides
- How much does mould removal cost in the UK? (2026 guide)
- Damp and mould in rented homes: landlord duties and Awaab's Law explained
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