Where Does Mould Hide? The Most Overlooked Spots You Should Test
, by Tatianna Gerard, 12 min reading time
When most people think of mould, they picture the obvious signs—black or green patches creeping across walls, a musty smell lingering in the air, or visible specks forming on bathroom tiles. But what many homeowners don’t realise is that hidden mould can be just as dangerous, if not more so, than the mould you can see.
Mould thrives in damp, humid, and poorly ventilated spaces. While visible mould growth is a clear indication of a problem, the real danger often lurks out of sight—behind walls, under flooring, inside air conditioning systems, or in places you rarely inspect. Because these hidden colonies continue to spread unnoticed, they can release spores into the air, affecting indoor air quality and leading to allergic reactions, respiratory issues, and long-term structural damage.
Ignoring hidden mould can be costly. By the time it becomes visible, the infestation is often severe, requiring extensive (and expensive) remediation.
This guide will walk you through the most overlooked spots where mould hides in homes, offices, and other indoor spaces.
Common hidden mould hotspots that you should regularly test and monitor
1. Air conditioning & HVAC systems
Your air conditioning and HVAC system could be circulating mould spores throughout your home without you even realising it. These systems create the perfect environment for mould growth—damp filters, condensation buildup, and dark, enclosed spaces provide an ideal breeding ground.
Where mould hides:
- Air filters that absorb dust and moisture
- Ductwork where condensation builds up
- Evaporator coils and drip pans that collect moisture
📌 Tip: Regularly replace AC filters, clean ducts, and schedule professional HVAC maintenance to prevent mould from spreading through your ventilation system. You can even use SAN-AIR’s mould removal gels specifically for use in air-conditioning systems to prevent mould growth after cleaning.
Our product recommendations:
- For use in air conditioning systems and air handlers - SAN-AIR V3R Air Conditioning Reactive Gel
- For large and small ducted air conditioning systems - SAN-AIR V3R Air Handler Reactive Gel
- For Split System air conditioners - SAN-AIR V3R Split System Reactive Gel
2. Under carpets & flooring
Spills, leaks, and high humidity can turn carpets and floorboards into hidden mould breeding grounds. Moisture can seep into carpet padding, wooden subfloors, and even concrete, allowing mould to thrive out of sight.
Where mould hides:
- Under carpets and rugs in humid or high-traffic areas
- Beneath laminate or wooden flooring, especially in kitchens and bathrooms
- Along the edges of flooring near walls where moisture collects
📌 Tip: If you notice a musty smell or warping in your flooring, lift a section to check for signs of mould. Ensure spills are dried immediately, and consider using a dehumidifier in damp areas.
Our product recommendations:
- To wipe floor surfaces - SAN-AIR Surface Mould Remover
- To clean mould from carpets and rugs - SAN-AIR LD Concentrate - Natural Mould Cleaner & Sanitiser (requires dilution before use, with recommended ratios of either 20:1 or 50:1)
3. Behind walls & wallpaper
Even if your walls look clean, mould could be thriving behind them—especially in homes with leaky pipes, condensation issues, or past water damage. If you have peeling wallpaper, bubbling paint, or unexplained damp patches, you may have hidden mould growth.
Where mould hides:
- Behind wallpaper and wall panels, especially in humid rooms
- Inside drywall or plasterboard due to leaks or condensation buildup
- Behind kitchen or bathroom splashbacks
📌 Tip: If you suspect hidden mould, use a moisture meter or infrared camera (normally used by professionals) to check for damp spots inside walls.
Our product recommendation:
-
To wipe wall surfaces - SAN-AIR Surface Mould Remover
Check out related blog article: How to Get Rid of Mould from Bathroom
4. Inside cupboards & wardrobes
Cupboards and wardrobes are often neglected, making them prime spots for mould growth. These enclosed spaces trap moisture from humid air, especially if there’s poor airflow or a nearby water source (such as a leaking pipe or an unventilated bathroom).
Where mould hides:
- The back walls of wardrobes, particularly in damp rooms
- Inside kitchen cabinets under sinks
- In linen closets where moisture from laundry can accumulate
📌 Tip: Keep wardrobe doors slightly open for airflow, use moisture absorbers, and store clothes completely dry to prevent mould.
Check out related blog article: How to Treat and Prevent Mould on Your Clothes and In Your Wardrobe for more tips on cleaning your wardrobe.
Our product recommendations:
- To wipe the inside of the wardrobes/cupboards - SAN-AIR Surface Mould Remover
- To wash clothes infested with mould growth - SAN-AIR LD Concentrate - Natural Mould Cleaner & Sanitiser (Run the diluted solution with ratio 20:1 or 50:1 through the washing machine to treat mould and odours on clothes.
5. Ceiling & roof spaces (attics, crawl spaces)
Attics and crawl spaces are often forgotten, but they’re high-risk areas for mould due to poor ventilation, roof leaks, and condensation buildup. Since they are rarely inspected, mould can spread unchecked for months or even years.
Where mould hides:
- On attic insulation and beams exposed to condensation
- Around roof leaks or near broken shingles
- In poorly ventilated crawl spaces beneath homes
📌 Tip: Check your attic or crawl space seasonally, especially after heavy rain. Ensure proper ventilation and insulation to reduce moisture retention.
Our product recommendations:
- To wipe wall surfaces or ceiling - SAN-AIR Surface Mould Remover
- To prevent mould growth in enclosed small spaces - SAN-AIR Caravan, Boat & Storage Reactive Gel (use together with an air diffuser for optimal distribution throughout the area).
6. Window frames & sills
Windows are one of the most common but overlooked places for mould growth. Condensation buildup, particularly in winter or humid months, creates a consistently damp environment—perfect for mould spores to take hold.
Where mould hides:
- Along window sills where condensation pools
- In the tracks of sliding windows and door frames
- On curtains and blinds that retain moisture
📌 Tip: Wipe down condensation daily in colder months, and open windows regularly for airflow. Consider using double glazing or weather stripping to reduce condensation.
Our product recommendation:
-
To wipe window frames and sills - SAN-AIR Surface Mould Remover
7. Behind large furniture (beds, sofas, cabinets)
Furniture placed against exterior walls can block air circulation, creating pockets of trapped humidity where mould can grow unnoticed. If your furniture feels damp to the touch or you notice a musty smell when moving it, you may have mould thriving behind it.
Where mould hides:
- The backs of beds and headboards pressed against walls
- Behind wardrobes and cabinets in damp rooms
- Underneath sofas in poorly ventilated spaces
📌 Tip: Leave a small gap between furniture and walls to allow for airflow. Regularly move and clean behind large furniture to prevent mould buildup.
Our product recommendation:
-
To treat and prevent mould growth in bedrooms or living spaces - SAN-AIR Mould Treatment Starter Pack
8. Washing machines & dishwashers
Washing machines and dishwashers create the perfect environment for mould—warm, humid, and often neglected. Rubber seals and internal compartments stay damp, allowing mould to thrive unnoticed.
Where mould hides:
- Inside rubber door seals, particularly in front-loading washers
- In detergent drawers where residue and moisture accumulate
- Underneath washing machines and dishwashers due to leaks
📌 Tip: Leave washing machine doors open after use to air dry the drum and wipe rubber seals regularly to prevent mould buildup.
Our product recommendations:
- To wipe the inside of washing machine and dishwashers - SAN-AIR Surface Mould Remover or SAN-AIR LD Concentrate - Natural Mould Cleaner & Sanitiser
- To prevent mould growth in laundry rooms - SAN-AIR™ Mould Removal Bundle
9. Fridge drip trays & food storage areas
Many people don’t realise that fridge drip trays and storage compartments can be major mould hotspots. Condensation, food spills, and neglected crisper drawers create the perfect environment for mould growth.
Where mould hides:
- In the fridge drip tray (often ignored during cleaning)
- Under vegetable crispers where moisture collects
- Behind the fridge, where condensation and dust accumulate
📌 Tip: Clean fridge drip trays regularly and check behind the fridge for hidden moisture buildup.
Our product recommendations:
-
To wipe the fridge and surrounding areas - SAN-AIR Surface Mould Remover
10. Basements & storage areas
Basements, garages, and storage rooms tend to be poorly ventilated, making them a prime location for mould growth. Stored cardboard boxes, furniture, and clothes absorb moisture, allowing mould to spread over time.
Where mould hides:
- On stored clothes, books, and cardboard boxes
- In corners where moisture accumulates
- Near water heaters or exposed plumbing
📌 Tip: Keep storage areas dry and ventilated. Use sealed plastic containers instead of cardboard for storing items to prevent mould growth.
Our product recommendation:
-
To prevent mould growth in storage areas - SAN-AIR Caravan, Boat & Storage Reactive Gel (use together with an air diffuser for optimal distribution throughout the area).
11. Caravans & boats
Caravans and boats are high-risk areas for mould growth due to limited airflow, fluctuating humidity levels, and frequent exposure to moisture. During the off-season, when they are sealed up for long periods, condensation and trapped humidity create ideal conditions for mould to thrive.
Where mould hides:
- In seat cushions, mattresses, and upholstery that absorb moisture
- Behind wall panels and in storage compartments where air circulation is minimal
- In cupboards, under sinks, and near water tanks due to condensation buildup
- Inside air conditioning vents and window seals, especially after prolonged periods of no use
📌 Tip: Use moisture absorbers like SAN-AIR Caravan, Boat & Storage Reactive Gel and dehumidifiers when your caravan or boat is not in use. Ensure proper ventilation by opening windows and air vents periodically, and store cushions and fabrics in breathable containers to prevent mould buildup.
Check out related blog article: How Do You Get Rid of Mould in Your Caravan or Boat?
Don’t let hidden mould catch you off guard
Mould isn’t always easy to spot, but that doesn’t mean it’s not there. While most people focus on visible mould, the real danger often lies in hidden, damp areas that go unchecked—inside air conditioning units, behind walls, under carpets, and even in everyday appliances like washing machines and fridges.
By knowing where to look and when to test, you can stay ahead of mould problems before they escalate. Whether you live in a house, apartment, caravan, or own a boat, regular mould testing in overlooked spots can help protect your health, your home, and your belongings.
Think mould might be hiding in your home? Take action today with the SAN-AIR Mould & Bacteria Test Kit—a simple, effective way to detect hidden mould in the air, water or on the surface!
Shop the SAN-AIR Mould & Bacteria Test Kits
