7 hidden mould hotspots to check in your home — you might be surprised by where spores love to lurk

Mould has an unpleasant habit of lingering where you’d least expect it, quietly spreading behind wardrobes, under carpets, and in other concealed spots around your home. But hidden mould isn't just unsightly – if left unchecked, it can wreak havoc on your health and interiors. The question is, where is it hiding?

From toxic black mould that clings to walls to fluffier, powdery types of mould often found on fabrics or wooden surfaces, these unwanted visitors thrive in dark, damp corners. They love spaces with little airflow, and before you know it, they’re leaving behind their tell-tale musty odour.

Thankfully, mould and air quality experts say there’s a solution. By uncovering these hidden mould hotspots, you can stop it in its tracks and keep your home feeling fresh.

A cautionary tale on hidden mould

Homebuilding & Renovating's editor, Beth Murton, has firsthand experience of discovering hidden mould: "When we moved into our current home and did a complete house renovation, we got a surprise when we eventually ripped out the old fitted wardrobes in the main bedroom," she explains. "The wall was completely black behind the wardrobes, which had been fitted against a cold, outside wall. Moisture and mould had clearly been building up for a long period of time, but was hidden from sight by the wardrobes. We had to dry out and thoroughly clean the walls before we could redecorate, and we fitted our new wardrobes against a different wall in the room to prevent the issue occurring again."

Frustratingly, Beth's experience is surprisingly common among UK homeowners. Fortunately, there are plenty of ways to get rid of mould once you know where to look.

What causes hidden mould to develop?

“During the colder months, chances of condensation forming in the home due to moisture levels increase compared to warmer months and when cold temperatures and moisture are combined, mould is almost inevitable," explains James Longley, managing director at Utility Bidder.

Michael Rubino, author of The Mold Medic, agrees: "Anywhere moisture is present is an area where mould can pop up. This could be rooms with higher humidity, places with a hidden leak, structural issues, or some other avenue for moisture problems."

"Lack of cleaning and maintenance are also high on the list for allowing microbial growth," Rubino adds. "The more spores in an environment and organic matter they can use for growth, the higher the chance colonies will develop."

Michael Rubino

Michael Rubino is a mould and air quality expert, author of The Mold Medic: An Expert’s Guide on Mold Removal and founder of HomeCleanse. Michael is a council-certified mould remediator by IICRC and ACAC and a contributing member, sponsor, and speaker for the Indoor Air Quality Association.

Areas to pay close attention to include:

1. Behind furniture

Furniture placed against cold external walls can trap moisture, particularly if the wall is poorly insulated. Without proper air circulation, condensation builds up, creating the perfect conditions for mould to thrive. Wardrobes, sofas, and bookcases are common culprits, as their bulky dimensions limit airflow and allow damp to linger.

Spot the signs: Clothes stored in affected wardrobes may smell of damp. Look for discolouration or black spots on walls behind furniture. Powdery green mould (Cladosporium) may also appear on wooden surfaces.

The solution: Leave a gap between furniture and the wall to allow airflow. Use mould-resistant paint in problem areas and invest in a dehumidifier to reduce moisture levels. Damp absorbers inside wardrobes can also help.

Tools for battling hidden mould

2. In loft spaces

"With improper exhaust ends, roof leaks, ventilation issues, or insulation problems, there are many routes for moisture to enter loft spaces," explains Michael Rubino. Warm, moist air rising from below meets colder loft temperatures, causing condensation on beams, insulation, or stored items.

Spot the Signs: Look for dark spots or white patches on beams, damp insulation, or a musty smell. If left unchecked, mould here can cause structural damage and impact indoor air quality.

The Solution: Proper loft insulation and ventilation are the key to keeping these spaces mould-free. Install vents or breathable membranes to let moisture escape, and check for roof leaks regularly. Avoid cluttering your loft, as stored items can block airflow. If mould appears, treat affected areas with a mould remover and replace any damaged insulation.

3. Beneath carpets or floors

Moisture can creep beneath floors and carpets from spills, leaks, or rising damp. Hard floors, such as wood or laminate, are vulnerable if gaps or seals are inadequate, while carpets can harbour moisture in their underlay.

Spot the signs: Paul Hambidge, managing director at Factory Direct Flooring, says: "Mould may appear as little spots – black, grey, brown, or green – or even as fuzzy patches. It’s one of the most common bacteria types on floors, especially in kitchens and bathrooms."

The solution: Hambidge notes, "Vacuuming was the most effective cleaning technique in our tests, reducing mould bacteria by 71% compared to 30% with wipes." Be cautious not to spread spores when vacuuming—contain the area and clean tools thoroughly after use.

To prevent mould developing under floors, clean up spills on hard floors immediately and dry them thoroughly. In basements, use moisture barriers under carpets or opt for washable rugs. For vinyl or linoleum, lift and treat the affected area, ensuring it dries completely before reinstalling these materials.

Paul Hambidge

Paul has 32 years of flooring industry knowledge and experience from both an installation and manufacturing perspective. As director of Factory Direct Flooring Ltd, he has been involved in all aspects of flooring and has worked with some of the largest producers of wood flooring, vinyl flooring and laminate floors.

4. Behind curtains

Curtains covering windows prone to condensation often absorb moisture, creating a hidden hotspot for mould. Fabric touching the windowsill is especially vulnerable.

Spot the signs: Look for dark patches or damp fabric along the curtain hem. A musty smell or mould on window frames or walls may also indicate a problem.

The solution: Opt for thermal-lined or moisture-resistant curtains where possible and keep your windows clear of condensation by wiping them with a squeegee every morning. Wash or dry-clean your curtains regularly and improve your home ventilation by opening windows for 5-10 minutes each day – also known as house burping.

5. Inside kitchen cupboards

Kitchens are prime targets for mould due to leaky pipes, trapped steam, and spills. Under-sink cupboards are particularly vulnerable to mould from unnoticed leaks or humidity.

Spot the signs: Signs include warped or damp wood and a musty smell when opening cupboard doors. In severe cases, mould may spread to stored items or food packaging as well.

The solution: Fix leaks promptly and keep your cupboards dry. Use moisture-resistant mats for added protection and find ways to improve kitchen ventilation to control humidity levels.

6. Inside the toilet tank

Few homeowners think to check for mould inside the toilet tank, but Michael Rubino explains it’s a hidden risk: "While the lid isn’t hermetically sealed, there’s little air transfer. It’s more likely that spores from another mould colony in the home found their way into this wet oasis."

Spot the signs: Look for discolouration, slimy residue, or a musty smell inside the tank.

The solution: "Start with an at-home dust test like The Surface Dust test from Home Air Check to determine if there’s a problem. Mould spores and mycotoxins settle where dust settles. High levels in your dust suggest a hidden issue that a mould inspector should investigate," says Rubino.

7. Mattresses

From night-time sweating and accidental spills to high humidity levels, mattresses are prime targets for moisture build-up. Combined with organic materials like skin cells, it doesn’t take long for mould to make itself at home.

A spokesperson for WinstonsBeds.com says: “We recommend rotating your mattress about once a month to promote good airflow, which can help prevent mould.

"Maintaining good hygiene, such as promptly cleaning spills and regularly washing linens, also discourages mould growth. Avoid drying damp clothes or towels in the bedroom or near the bed, and be sure to open a window to ventilate the room when it’s humid.

Spot the signs: Mould on mattresses can be identified by a musty smell and discoloration such as dark spots which may appear fuzzy or slimy.

The solution: Experts advise vacuuming the mattress first before applying a small amount of a mixture of warm water and rubbing alcohol. Allow the solution to sit on the mattress (but not soak it) before scrubbing it. After drying, spray the mattress with upholstery disinfectant to help prevent it returning.

FAQs

What other areas of the home are hidden mould hotspots?

There are several other surprising areas in your home where mould and mildew can quietly take hold:

Bathroom and Sink Fixtures: Showerheads and taps are often overlooked but can hold onto moisture for long periods. Without regular cleaning, these fixtures can quickly create the perfect breeding ground for mould.

Air Conditioning Return Vents: Poorly maintained AC return vents can collect dust, which in turn harbours mould spores. Add trapped moisture into the mix, and these vents become hotspots for microbial growth.

On/In Kitchen Appliances: Without regular cleaning, proper drying, and maintenance, kitchen appliances can accumulate moisture in hidden areas and crevices, creating the perfect environment for mould growth.

Basements: Poor basement ventilation, flooding, insulation issues, and high humidity are all reasons why these spaces are a magnet for moisture and mould.

Do clean homes get mould?

Yes, even clean homes can develop mould. Michael Rubino explains: "Mould can grow in as little as 24-48 hours provided the elements necessary for growth (food and moisture) are present." Preventing hidden mould hotspots, according to Michael, comes down to three key steps: reducing moisture levels in your home, minimising mould spores, and using air purifiers and dehumidifiers when needed.

Regular checks and a little extra care can go a long way in keeping your home mould-free and feeling fresh. For a more in depth guide to getting rid of mould, read our step by step instructions on removing mould from walls and removing mould from ceilings.