Winter vs. Summer Mould: What’s the Difference

June 24 2025, by Tatianna Gerard, 15 min reading time

Mould can be a problem at any time of year, but how and where it shows up in your home often depends on the season. Warmer months tend to bring more visible outbreaks in places like bathrooms, kitchens, and laundry areas — anywhere that stays warm and humid. In contrast, winter mould is often less obvious but just as persistent, thriving in cooler, enclosed spaces where condensation and damp air collect without much airflow.

For many households in Australia — especially those in river valleys, coastal regions, or older homes — dampness and mould are a seasonal concern. According to findings referenced in the Australian Parliamentary report on indoor biotoxin exposure, it’s estimated that between 10% and 50% of indoor environments across the country may be affected by damp conditions, creating ideal circumstances for mould growth year-round.

Thus, understanding the seasonal differences in mould behaviour can help you prevent it more effectively. In this article, we’ll explore how winter and summer mould differ, what to look out for in each season, and how to protect your home all year long.

What mould needs to grow (and how the seasons change things)

At its core, mould is a living organism — and like most organisms, it needs the right conditions to thrive. The three main ingredients for mould growth are:

Moisture (from condensation, leaks, humidity, or damp materials)
Organic material (like dust, fabrics, wood, and drywall)
Still air or poor ventilation

When these elements combine, mould spores — which are always present in the environment — can settle, grow, and begin to spread.

So, what changes between summer and winter?

While the basic recipe for mould remains the same, seasonal conditions affect how and where it develops.

In summer, high humidity and warm temperatures can speed up mould growth dramatically. Moisture from showers, cooking, or even sweating can linger in the air, especially in poorly ventilated rooms. Mould in summer often appears in bathrooms, on ceilings, around air conditioning units, or inside wardrobes where airflow is limited.

In winter, indoor mould thrives in different ways. Cold outside air colliding with warm indoor air leads to condensation on windows, walls, and ceilings — especially in bedrooms and living spaces that aren’t aired out regularly. We also tend to keep our homes shut tight to stay warm, which traps moisture inside. Everyday activities like cooking, drying clothes indoors, or using heaters without ventilation can increase indoor humidity, even if it doesn’t feel humid.

Unlike summer mould, which tends to grow quickly and visibly, winter mould can be more subtle, building up slowly in corners, behind furniture, or inside wardrobes where damp air quietly accumulates.

Where mould tends to show up in summer vs. winter

Mould doesn’t grow randomly — it favours certain locations depending on the time of year, the airflow in your home, and how moisture builds up in different environments. By understanding where mould is most likely to appear in each season, you can take early steps to address it before it becomes a bigger problem.

Common mould hotspots in summer

In summer, the main drivers of mould growth are heat and humidity. Even if your home feels dry, indoor moisture can build up through daily activities — especially in homes without good cross-ventilation or where insulation is lacking.

Here’s where mould typically shows up in warmer months:

Bathrooms and showers: Steam from hot showers creates the perfect humid microclimate for mould, especially on grout, ceilings, and behind shower curtains.
Laundry rooms: If you’re running the dryer regularly or drying clothes indoors, excess moisture can collect on walls and ceilings.
Wardrobes and closets: Closed-up spaces with poor airflow and warm, dark conditions can trap moisture — especially if clothes go in slightly damp or if the room shares a wall with a bathroom.
Ceilings and upper corners: Hot air rises — and so does humidity. Mould often shows up in high, hard-to-reach spots where condensation settles and airflow is weakest.
Inside air conditioning units: Dust and moisture that accumulate in filters and vents can create a breeding ground for mould — and spread spores through the air when the unit is switched on.

If your home tends to get stuffy, or you live in a humid region, summer mould can spread quickly — especially if ventilation isn’t consistent.

Common mould hotspots in winter

Winter might feel like the air is drier, but that’s not always the case indoors. When the temperature outside drops and we seal up our homes for warmth, we create conditions where condensation, stale air, and dampness can quietly take over.

Here’s where mould often shows up in winter:

Windowsills and window frames: Warm indoor air meeting cold glass creates condensation — often overnight. If water pools and isn’t wiped down, it seeps into wooden frames or builds up on sills, encouraging mould.
Behind furniture: Sofas, beds, and bookshelves placed against external walls can trap cold air and moisture, especially if there’s little airflow behind them.
Wardrobes and storage cupboards: Similar to summer, mould loves enclosed spaces with stagnant air. In winter, thicker clothing and closed doors can increase humidity and limit ventilation.
Ceilings and corners of poorly insulated rooms: Moisture from cooking, heaters, or even breathing can rise and settle on cold surfaces, especially in rooms that aren’t frequently aired out.
Bedrooms: This might surprise people, but bedrooms are often under-heated and under-ventilated in winter. Overnight, humidity from breathing collects in the air, condenses on walls and windows, and builds up slowly over time.

Even caravans, boats, and sheds stored away for the season can develop mould if moisture gets in and ventilation is limited — especially through cushions, curtains, or bathrooms left closed for long periods.

Is one season worse than the other?

When it comes to mould, both summer and winter have their own challenges — and neither season is inherently “worse.” Instead, each brings different risks based on how your home manages moisture, airflow, and temperature changes.

The answer depends on your home’s layout, insulation, climate, and lifestyle habits. A coastal home might struggle more in summer, while an older, poorly insulated house could see more winter mould issues. What matters most is knowing what to look for in each season — and being proactive about managing the underlying causes like moisture and airflow.

Comparing the two seasons

While mould thrives year-round under the right conditions, summer and winter mould differ in how they start, where they grow, and how quickly they spread. Here’s a quick side-by-side comparison to help you spot the signs:

Feature	Summer Mould	Winter Mould
Primary cause	High humidity and poor airflow	Condensation from temperature differences
Typical locations	Bathrooms, kitchens, wardrobes, AC units	Windows, ceilings, behind furniture, inside cupboards
Growth rate	Rapid due to warmth and moisture	Slower, more hidden growth
Visibility	Usually more obvious and surface-level	Often subtle or hidden behind/under items
Ventilation challenges	Closed-off rooms, limited airflow in heat	Sealed homes for warmth, poor air circulation
Risk factors	Humid climate, frequent steam/moisture indoors	Cold surfaces, lack of insulation, unventilated areas
Common signs	Musty smells, black/green patches, foggy mirrors	Condensation, peeling paint, damp window frames

Seasonal mould prevention tips for every home

Whether you’re facing summer’s humidity or winter’s condensation, the key to mould prevention lies in moisture control, proper ventilation, and routine maintenance. While the triggers may differ between seasons, the strategies to keep mould at bay remain surprisingly consistent — with just a few tweaks depending on the weather.

Summer mould prevention tips

Use exhaust fans in bathrooms, kitchens, and laundry areas to remove steam quickly after showers, cooking, or running appliances.
Keep wardrobes and cupboards slightly ajar where possible to promote air circulation, especially during heatwaves or humid days.
Clean and service air conditioners regularly, especially filters and ducts, to prevent moisture build-up and mould inside the unit.
Avoid drying clothes indoors, or use a well-ventilated area with a dehumidifier if you must.
Wipe down wet surfaces regularly, especially in bathrooms and on tiled floors, to stop moisture pooling and seeping into grout or walls.

Winter mould prevention tips

Open windows when weather permits, even briefly, to allow stale, moisture-laden air to escape and fresh air to circulate.
Keep furniture slightly away from walls, especially external ones, to reduce condensation build-up and allow airflow behind large pieces.
Use thermal or double-glazed curtains or window films to reduce indoor condensation on glass surfaces.
Wipe down condensation from windows and frames daily, especially in bedrooms where moisture from breathing can build up overnight.
Avoid overusing unflued gas heaters, which release moisture into the air — consider electric or reverse-cycle heating options instead.

🕒 All-year essentials

Fix leaks immediately, whether from pipes, roofs, or around windows. Even small, slow leaks can lead to serious mould growth over time.
Vacuum and dust regularly, especially in hidden corners, as organic matter (like skin cells, dust, and dirt) provides food for mould spores.
Monitor humidity levels with a hygrometer — aim for indoor humidity between 30%–50%.

And while prevention goes a long way, there are times when testing for mould becomes necessary. If you start noticing a musty odour, recurring damp spots, or unexplained allergy-like symptoms in your household — it might be time to investigate further. Mould can hide in wall cavities, under floorboards, or in ceiling spaces, especially after seasonal changes or water damage.

In many cases, you can do a quick and effective check using a DIY mould test kit to get clarity on what’s lurking in the air or on surfaces. But depending on the extent of the issue, it’s also worth knowing when to test on your own and when it’s time to bring in a professional.

The natural way to protect your home: Meet the SAN-AIR Mould Solutions

When it comes to mould, prevention is just as important as treatment — and that’s where SAN-AIR comes in. Proudly Australian-made and backed by scientific testing, SAN-AIR products are formulated using natural, plant-based active ingredients. They’re designed not only to remove visible mould, but also to target airborne spores and prevent regrowth — all without relying on harsh chemicals.

Most importantly, SAN-AIR offers a complete mould solution: from testing and removal to long-term prevention, and here’s how you can use the product ranges, from start to finish:

Step 1: Test the air and surfaces

If you’re unsure whether mould is present — or where it might be hiding — the SAN-AIR Mould & Bacteria Test Kit is a simple, DIY tool that helps detect airborne and surface-based mould. It’s ideal for homes, offices, and even cars or storage spaces where the source of musty smells or symptoms isn’t immediately obvious.

Read our detailed guide to using the SAN-AIR test kit here.

Step 2: Remove mould safely and effectively

Once you know where mould is hiding, removing it properly is key. SAN-AIR’s removal products offer targeted solutions for different surfaces — without the fumes and hazards of bleach or chemical sprays.

SAN-AIR Surface Mould Remover Spray

A ready-to-use natural spray for wiping down walls, tiles, and hard surfaces.

SAN-AIR LD Concentrate

Dilute for tougher jobs like tile grout, dishwashers, and even laundry with mould stains. Gentle yet powerful on a wide range of materials.

SAN-AIR HVAC-R Anti-Microbial Surface Sealer Concentrate

Designed for HVAC systems, this concentrate helps seal surfaces and prevent the build-up of mould and biofilm in residential and commercial ductwork.

❗Be sure to equip yourself with the right PPE like P2 masks, gloves, and goggles to protect yourself from the airborne mould spores when cleaning.

Shop our collection of PPE solutions.

Step 3: Prevent future outbreaks

Mould prevention isn’t a one-time fix — especially in areas prone to moisture or limited airflow. SAN-AIR’s prevention products work continuously to purify the air and control mould spore activity in indoor spaces.

SAN-AIR Mould Gone Gel

Ideal for everyday use in homes, this gel gradually releases natural actives to reduce airborne mould and bacteria.

SAN-AIR Caravan, Boat & Storage Gel

Formulated for confined or infrequently used spaces prone to musty build-up, especially during winter storage.

SAN-AIR V3R Split System Reactive Gel

Perfect for split system air conditioners, helping to maintain clean air flow and reduce microbial growth.

SAN-AIR V3R Air Conditioning & Air Handler Gel Diffusers

Designed for ducted AC systems and handlers, these gels provide protection in larger, commercial-scale systems too.

Explore more SAN-AIR range of products at Aussie Pharma Direct.

Stay one step ahead of mould — whatever the season

From condensation on winter windows to humid summer air, every home faces different mould triggers throughout the year. Regular maintenance, good airflow, and moisture control are essential — but equally important is having the right tools on hand. Whether it’s testing for hidden spores, removing visible growth, or preventing it from coming back, natural solutions like the SAN-AIR Mould Solutions make it easier to stay mould-free without compromising your indoor air quality.

Remember: the sooner you act, the easier mould is to manage. So, don’t wait for the smell to settle in — a little prevention now can save you a lot of cleaning (and sneezing) later.