Winter Mould Myths: Common Mistakes Homeowners Make

June 24 2025, by Tatianna Gerard, 8 min reading time

When the temperature drops, most of us focus on keeping warm, not fighting mould. But winter is one of the prime seasons for mould growth, especially in homes that are sealed tight against the cold. And while summer humidity tends to get the blame, it’s often the hidden moisture and poor ventilation during winter that allow mould to thrive — quietly and out of sight.

Despite good intentions, many homeowners fall into familiar traps when it comes to preventing or treating mould during the colder months. From cranking up the heat without improving airflow, to relying on quick-fix cleaning hacks or solutions that don’t actually work, these common missteps can make things worse in the long run.

In this article, we’ll unpack some of the biggest winter mould myths — and the small changes that can make a real difference in keeping your home dry, healthy, and mould-free.

Myth #1: “Mould only grows in summer”

It’s a common belief that mould is only a problem when it’s hot and humid — but that’s far from the full picture. While summer provides the moisture and warmth, winter creates the perfect storm indoors: cooler temperatures outside, heated air inside, and poor ventilation as we try to keep the warmth in.

The result? Condensation. It forms on windows, walls, ceilings, and even behind furniture — especially in rooms where air doesn’t circulate well. This trapped moisture becomes a breeding ground for mould, particularly in older homes, or those with inadequate insulation.

In fact, some winter environments are even more conducive to hidden mould growth than in summer. While summer mould is often more visible (think steamy bathrooms or laundry rooms), winter mould tends to develop quietly, often going unnoticed until it starts to cause stains, damage, or respiratory symptoms.

Myth #2: “Turning up the heat will dry it out”

It seems logical — warm air dries things out, right? But when it comes to mould prevention, simply turning up the heat isn’t a silver bullet. In fact, heating your home without proper ventilation can make the mould problem worse.

Here’s why: warm air holds more moisture. When you heat your home during winter — especially with no airflow — that moisture accumulates and eventually settles on cold surfaces like windows, walls, and ceilings. This is why you might notice condensation in the morning, even if the house felt warm the night before.

This trapped moisture becomes the perfect feeding ground for mould. And because it’s invisible at first, it often goes unnoticed until the mould is well established.

What really works is a balance of warmth and airflow. Opening windows periodically, using exhaust fans in bathrooms and kitchens, or running a dehumidifier can make a significant difference. So yes, keep your space warm — but let it breathe too.

Myth #3: “If you can’t see mould, it’s not there”

Out of sight, out of mind — but not out of your home. One of the biggest mistakes homeowners make in winter is assuming no visible mould = no problem. Unfortunately, mould doesn’t always grow where it’s easy to spot.

In cooler months, it’s common for mould to thrive behind furniture, inside wardrobes, under carpets, and within poorly ventilated roof spaces. You might not see it, but you might notice musty smells, lingering dampness, or experience respiratory symptoms like sneezing, coughing, or headaches — all signs that something unseen may be growing.

Winter mould is especially sneaky because homes are usually closed up tightly to retain warmth, reducing airflow and trapping spores indoors. This gives mould the quiet, still environment it needs to spread behind the scenes.

That’s why it’s a good idea to inspect hidden corners of the home, particularly after rain or cold snaps. And if you suspect something is off — even without visible signs — you can always test for mould at home with products like the SAN-AIR Mould & Bacteria Test Kit, which detects both airborne and surface mould before it becomes a bigger issue.

Myth #4: “A quick spray of bleach will do the trick”

Bleach has long been the go-to for cleaning mould, but here’s the truth: it’s not as effective as you might think — especially on porous surfaces like plaster, wood, or grout. While it may remove the visible stain, bleach often fails to kill the mould at its source. The result? It comes back — sometimes even faster than before.

What’s more, using bleach indoors (especially in closed-up winter homes) can release harsh fumes that irritate the skin, lungs, and eyes. For families with children, pets, or anyone with allergies or asthma, this can do more harm than good.

Mould roots (called hyphae) can penetrate deep into surfaces where bleach can’t reach. So even though things might look clean on the outside, the mould is still alive beneath — just waiting for the right conditions to grow back.

The problem lies in how bleach works: it’s a biocide, which means it kills microbes on contact — but it doesn’t always stop them from coming back. That’s why more people are now turning to biostat-based mould cleaners instead. A biostat doesn’t just kill mould; it inhibits its growth over time, helping to prevent regrowth in treated areas. We explore this concept further in our blog, Why Vinegar, Bleach and Other Chemicals Fail to Tackle Mould.

Instead of harsh chemicals, look for natural, purpose-made mould removers that are safe for indoor use and actually work at a microbial level. For example, SAN-AIR Surface Mould Remover is plant-based, TGA-listed, and designed to kill surface mould safely while being gentle on indoor air.

Myth #5: “If it’s just a small patch, it’s not a big deal”

It’s easy to dismiss a tiny spot of mould as harmless — maybe a speck on the ceiling, or a dark patch near the window frame. But even a small visible patch could be a sign of a much larger problem behind the scenes.

Mould is rarely isolated. That little cluster on your bathroom wall could mean there’s excess humidity, poor ventilation, or even a hidden leak at play. And since mould reproduces by releasing spores into the air, even a minor growth can affect your indoor air quality and potentially trigger respiratory symptoms.

Small doesn’t always mean safe. In fact, some of the most dangerous types of mould — like Stachybotrys chartarum, often called “black mould” — can start small and spread rapidly under the right conditions.

The takeaway? Don’t wait for it to spread. Addressing mould early on makes it easier (and cheaper) to manage, and helps prevent it from affecting your health or damaging your home. If you’re unsure how far the mould has spread or whether it’s safe to treat yourself, you can test for mould at home using a DIY kit, or consult a professional to assess the situation.

How to avoid these mistakes this winter

Now that we’ve debunked some of the most common winter mould myths, let’s talk about what you can do instead — because preventing mould is far easier (and safer) than dealing with a full-blown infestation.

Here are a few practical steps to help you stay ahead of the mould game:

✅ Ventilate smartly – Even during the cold months, open windows for short bursts to let stale, damp air escape. Use exhaust fans in bathrooms and kitchens, and avoid drying clothes indoors when possible.

✅ Keep humidity in check – Use a hygrometer to monitor indoor humidity. If it’s consistently above 60%, consider using a dehumidifier to bring it down.

✅ Look beyond what you can see – Don’t ignore musty smells or damp corners. These are often early signs that mould may be forming somewhere hidden.

✅ Use the right cleaning products – Skip the bleach and harsh chemicals. Opt for mould removal solutions that are biostat-based, like the SAN-AIR Mould Removal range, which not only eliminates mould but helps prevent it from returning.

✅ Test when in doubt – If you suspect hidden mould or want peace of mind, a DIY test kit like the SAN-AIR Mould & Bacteria Test Kit can help confirm what you’re dealing with — before it gets worse.

✅ Be proactive in storage areas – For spaces like wardrobes, boats, caravans, or storage rooms, prevention is key. Products like the SAN-AIR Mould Gone Gel or SAN-AIR™ Caravan, Boat & Storage Reactive Gel can help keep the air clean and stop mould from settling in.

Conclusion

When the weather turns cold the cosy indoor environment can sometimes invite an unwelcome guest: mould. Whether it’s believing bleach is enough, ignoring a musty smell, or underestimating that tiny patch in the corner, these assumptions can put your home — and your health — at risk.

You don’t need to overhaul your home to stay on top of mould. A few small, informed changes — better airflow, moisture control, and the right cleaning tools — can make a big difference.