Black spots around window frames, a musty smell behind a wardrobe or dark patches on a bathroom ceiling can all be signs of mould. Mould grows where moisture persists. Cleaning the visible patch is only part of the solution: you also need to identify and address what is making the area damp.
This guide explains how to distinguish condensation from leaks, what steps may help prevent mould returning, when professional help is appropriate and what renters in England can do.
Why mould grows in homes and how to prevent it
Why does mould grow indoors?
Mould is a fungus. Its spores are present in the environment, but growth becomes a problem when surfaces remain damp. The moisture might come from ordinary household activities, a cold surface where condensation forms, a leaking pipe or rainwater entering through a building defect.
The UK government’s guidance on damp and mould in homes explains that condensation is common, but warns against assuming that every mould problem is caused by occupants’ habits. More than one cause can be present.
How to identify where the moisture is coming from
Look at where the mould appears, when the area becomes damp and whether the problem changes with the weather. These clues are useful, but they do not replace a professional diagnosis.
| What you notice | Possible cause | Useful next check |
|---|---|---|
| Droplets on windows, cold corners or behind furniture | Condensation on cooler surfaces | Check ventilation, heating patterns and moisture from cooking, showers or drying clothes. |
| Staining that worsens after rain | Water entering from outside | Have gutters, roofing, external walls or window seals checked. |
| A persistent localised wet patch near pipes or a bathroom | Plumbing leak | Arrange a plumbing or building inspection rather than repeatedly cleaning the surface. |
| Musty smell with little visible mould | Concealed moisture or mould | Seek an assessment before disturbing walls, flooring or other materials. |
For an explanation of why moisture collects on cold glass, see why condensation forms on windows. For a practical room-by-room approach, see our window-condensation troubleshooting guide.
Why mould can be worse in winter
Windows and external walls get colder in winter, while people may ventilate less to retain heat. Cooking, bathing and drying laundry still release moisture into indoor air. When humid air meets a sufficiently cold surface, water can condense and leave the surface damp.
Bathrooms, kitchens, window frames and areas behind wardrobes placed tightly against external walls can be particularly vulnerable. That does not mean every mouldy wall has the same cause: damaged roofing, defective seals and hidden leaks also need to be considered.
Practical ways to reduce condensation-related mould
- Remove moisture at source: run an effective bathroom extractor during and after showers, and use an extractor that vents outside when cooking, where available.
- Prevent moisture spreading: close the bathroom door during a shower and use lids on pans where practical.
- Dry laundry carefully: dry it outdoors when feasible or use a suitable dryer. If air-drying indoors is unavoidable, ensure the space has appropriate ventilation.
- Maintain suitable heating and ventilation: avoid allowing rooms to remain unnecessarily cold, and do not obstruct designed ventilation openings or extractor fans.
- Allow airflow around furniture: leaving some space behind large items against cold external walls may help, where the layout allows.
- Fix leaks promptly: no amount of window opening will repair a leaking pipe, roof or wall.
A simple hygrometer can help you observe changes in indoor relative humidity after showers or laundry drying. It cannot, by itself, diagnose why a wall is damp. Keep brief notes of where condensation appears, when it happens and what changes after ventilation or repairs. This can be useful if you need a landlord or professional to investigate.
Will a dehumidifier stop mould?
A dehumidifier removes moisture from the air and may help manage condensation. It is not a substitute for repairing a leak, addressing failed ventilation or resolving another building defect. Similarly, heating alone is not a complete fix if moisture continues to accumulate.
Why mould returns after cleaning
Wiping away visible mould does not necessarily remove the conditions that allowed it to grow. If a window reveal becomes wet every night, or a roof continues leaking, the affected surface can become mouldy again. Government guidance advises identifying and dealing with the underlying source of moisture alongside removing the mould.
Do not simply paint over active mould or damp. Identify and resolve the source of moisture, arrange appropriate cleaning or remediation, and allow materials to dry before redecorating.
Is mould harmful to health?
Damp and mould can affect the airways and lungs and may also affect the eyes and skin. Exposure is associated with respiratory symptoms and can worsen asthma. Some people, including young children, older people and those with respiratory conditions or weakened immune systems, may be more vulnerable. These risks are described in the UK government health guidance.
Seek advice from a healthcare professional if you are concerned about symptoms. For severe breathing difficulty or another medical emergency, seek urgent medical help. Damp and mould problems should be addressed promptly rather than waiting for illness to develop.
Should you remove mould yourself?
Very small areas of condensation-related surface mould may sometimes be cleaned with a suitable mould-and-mildew product, following the manufacturer’s instructions. However, larger areas, recurring growth, concealed mould and problems involving building defects should be assessed and handled by appropriately qualified professionals.
For small-scale cleaning, government guidance advises suitable protection, including gloves, eye protection and an appropriate mask, and ventilation during and after the work. Avoid dry brushing or unnecessarily disturbing affected materials, which can release spores. Never mix cleaning chemicals. People with relevant health vulnerabilities should seek advice rather than undertaking exposure-prone cleaning themselves.
Porous materials such as carpets or ceiling tiles may not be safely recoverable once significantly affected. Follow professional advice rather than attempting to seal contamination inside the material.
What should you do if you rent your home?
If you rent, report damp or mould to your landlord or housing provider promptly. Keep dated photographs, record where the problem occurs, and save messages or repair requests. Describe leaks, broken ventilation and any relevant health concerns. Do not assume that structural or persistent mould problems are solely yours to resolve.
In social housing in England, Awaab’s Law guidance for tenants explains specific timescales for emergency hazards and significant damp-and-mould hazards. For qualifying significant damp-and-mould hazards, social landlords must investigate within 10 working days and make the hazard safe within 5 working days after the investigation. Emergency hazards have a 24-hour timeframe. These rules should not be presented as applying identically to every private tenancy or every minor patch of mould.
Housing rules and remedies differ across the UK. The GOV.UK guidance linked here chiefly concerns England; renters elsewhere should consult the relevant national housing authority or local advice service.
When to call a professional
Arrange an appropriate building or damp assessment when mould covers a substantial area, repeatedly returns, is associated with a persistent leak or unexplained wet patch, appears hidden within building materials, or may be affecting someone’s health. A professional can distinguish between condensation, penetrating damp, plumbing leaks and other causes; avoid paying for a particular treatment before the cause is properly established.
A simple checklist for investigating mould
- Record the problem: photograph the area and note when it is wet or smells musty.
- Look for the moisture source: consider cold surfaces, showers, cooking, laundry, leaks and rainfall.
- Check building systems: note whether extractor fans, ventilation openings, heating and gutters appear to be working as intended.
- Choose the right response: manage everyday condensation where feasible; report leaks or defects and seek professional assessment when needed.
- Follow up: check whether the cause has been fixed and whether damp or mould returns.
Frequently asked questions
Does opening windows prevent mould?
Ventilation may help reduce excess indoor moisture, but it will not fix a plumbing leak or defective roof. Follow the ventilation approach appropriate for your home.
Can mould grow behind a wardrobe?
Yes. Limited airflow next to a cold wall can contribute to dampness and mould growth. Moving furniture slightly away from the wall may help, but investigate ongoing moisture or visible damage.
Can I paint over a mouldy wall?
No. Painting over active damp or mould can conceal the problem without fixing it. Identify the source, arrange safe treatment and let the material dry first.
Sources and further reading
- GOV.UK: Understanding and addressing the health risks of damp and mould in the home (England; updated April 2026).
- GOV.UK: Awaab’s Law guidance for social housing tenants (England).
Information checked: 22 October 2026. This article provides general household information, not a property survey, legal advice or a medical diagnosis. If damp or mould is extensive, persistent or affecting health, seek appropriate professional advice.