Mould is one of the most common — and most misunderstood — problems in UK homes. An estimated 1 in 5 homes has a visible mould problem, and many more have hidden mould they don’t know about.
While a small patch of bathroom mould might seem harmless, mould is a serious health hazard that affects air quality and can cause respiratory problems, allergic reactions, and worse. Here’s how to deal with it properly.
Understanding Mould
What Is Mould?
Mould is a type of fungus that thrives in damp, warm environments. It reproduces by releasing microscopic spores into the air — and it’s these spores that cause health problems when inhaled.
The most common types found in UK homes:
- Aspergillus — appears in various colours, found on damp walls and food
- Cladosporium — olive-green to brown, common on fabrics, wood, and painted surfaces
- Stachybotrys chartarum (black mould) — the most concerning type, appears black or dark green, typically on persistently damp plasterboard and paper surfaces
What Mould Needs to Grow
Mould requires three conditions simultaneously:
- Moisture — relative humidity above 70% or direct water contact
- Warmth — mould grows most actively between 20–30°C, but can survive at lower temperatures
- A food source — organic materials like wood, paper, plaster, fabric, and even dust
Remove any one of these three conditions and mould cannot thrive. In practice, controlling moisture is almost always the most effective approach.
Health Risks
The NHS recognises damp and mould as significant health hazards:
- Respiratory symptoms — coughing, wheezing, breathlessness
- Allergic reactions — sneezing, runny nose, red eyes, skin rashes
- Asthma triggers — mould is a major trigger for asthma attacks, particularly in children
- Infections — people with weakened immune systems are vulnerable to fungal infections
- Long-term effects — prolonged exposure can cause chronic respiratory problems
Vulnerable groups — children, elderly people, those with existing respiratory conditions, and people with compromised immune systems are most at risk.
How to Safely Remove Mould
Small Areas (Less Than 1m²)
For minor mould on hard surfaces, you can clean it yourself:
What you’ll need:
- Rubber gloves
- Safety glasses
- A face mask (ideally FFP2 or FFP3)
- Fungicidal wash (available from DIY stores)
- Clean cloths
Steps:
- Open windows for ventilation
- Wear protective equipment — gloves, mask, and glasses
- Apply fungicidal wash according to the product instructions
- Leave to work for the recommended time
- Wipe away the mould with clean, damp cloths
- Dispose of cloths in sealed bags — don’t reuse them
- Allow the surface to dry thoroughly
- Apply mould-resistant paint once completely dry
Important: Do NOT use bleach. Bleach removes the colour of mould but doesn’t kill the root structure. The mould will return within weeks. Use a proper fungicidal product.
Large Areas or Persistent Mould
For mould covering more than 1m², in multiple rooms, or that keeps returning despite cleaning:
- Call a professional — large-scale mould removal releases significant quantities of spores
- Don’t disturb it — brushing or scraping mould before treatment spreads spores throughout the house
- Professional remediation uses containment, air filtration (HEPA), and industrial-strength treatments
- The underlying moisture source must be identified and fixed — cleaning mould without fixing the cause is a waste of time and money
Identifying the Moisture Source
Mould is always a symptom, not the disease. The four most common moisture sources:
1. Condensation
The most frequent cause. Warm, moist air meets cold surfaces, and water droplets form — creating perfect mould conditions.
Telltale signs:
- Mould in corners of rooms and behind furniture against external walls
- Window condensation in the mornings
- Mould in bathrooms and kitchens where moisture is generated
- Worse in winter when temperature differences are greatest
Solution: Improve ventilation, maintain consistent heating, and reduce moisture production. See our guide on condensation for detailed advice.
2. Penetrating Damp
Water entering through the building fabric from outside.
Telltale signs:
- Mould on walls that worsens during rain
- Damp patches on specific walls, often corresponding to defects visible outside
- Issues on upper floors suggesting roof or flashing problems
Solution: Repair the external defect — gutters, pointing, render, or roofing.
3. Rising Damp
Ground moisture travelling up through walls.
Telltale signs:
- Mould at the base of ground floor walls
- Tide marks and salt deposits
- Persistent regardless of weather
Solution: DPC injection or repair.
4. Plumbing Leaks
Hidden leaks behind walls, under floors, or in ceiling voids.
Telltale signs:
- Localised mould in specific spots, not related to external walls
- Damp patches that don’t correspond to rain
- Higher water bills than expected
- Sound of running water when nothing is turned on
Solution: Locate and repair the leak. A plumber may use thermal imaging or acoustic detection.
Long-Term Prevention
Ventilation — The Single Most Important Factor
- Extractor fans in every kitchen and bathroom, running for 15–20 minutes after use
- Trickle vents on windows — keep them open year-round
- Open windows briefly each morning for cross-ventilation
- Consider a PIV system (Positive Input Ventilation) — installed in the loft, it gently pushes filtered, dry air into the house, displacing moist air
- Never block airbricks or existing ventilation
Heating
- Keep all rooms above 15°C — even unused rooms
- Consistent, low heating is better than intense bursts
- Don’t leave unheated rooms with the door open to a heated room — warm air enters, hits the cold walls, and condensation forms
Moisture Management
- Use pan lids when cooking
- Don’t dry clothes on radiators — use a vented dryer or a dedicated drying room with ventilation
- Wipe down shower screens and tiles after use
- Keep bathroom doors closed while bathing (open after, with fan running)
- Move furniture 50–100mm from external walls
Mould-Resistant Products
For areas prone to mould:
- Mould-resistant paint contains fungicide — use in bathrooms, kitchens, and previously affected areas
- Anti-mould additives can be added to standard emulsion paint
- Mould-resistant silicone around baths and shower trays lasts longer than standard silicone
When to Get Professional Help
Contact a damp specialist if:
- Mould covers more than 1m² or appears in multiple rooms
- Mould keeps returning despite cleaning and improved ventilation
- You suspect structural damp (rising or penetrating)
- Anyone in the household has health symptoms that may be mould-related
- You’re buying or selling a property with mould issues
A professional damp survey identifies the exact moisture source and recommends targeted treatment — saving you from the cycle of cleaning mould that keeps coming back.
Get Expert Advice
Easy Damp provides thorough damp surveys across Greater Manchester and the North West. We’ll identify whether your mould is caused by condensation, structural damp, or another source — and provide honest, practical advice on the right solution.
Call 0161 527 6777 or book a survey online.
