Many Australians are familiar with finding mould or mildew in their homes — especially during humid summers or damp winters. But while the two are often confused, they’re not identical. Mould and mildew can look and smell similar, especially when they show up in bathrooms, wardrobes, or under kitchen sinks. But they differ in how they spread, how harmful they can be, and how you should clean them. And mistaking one for the other could mean treating it incorrectly or underestimating the potential damage.

While mildew is generally surface-level and easy to clean, mould can be more persistent and sometimes pose health risks, especially for people with allergies, asthma, or weakened immune systems.

This blog will help you figure out what’s growing in your space. You’ll learn what to look for, where mould and mildew typically shows up, and how to respond based on what you find.

Quick snapshot: Mould vs mildew

Feature	Mildew	Mould
Colour	White, grey, or yellow	Black, green, brown, or blue
Texture	Powdery, flat	Fuzzy, slimy, or patchy
Surface growth	Surface-level (tiles, walls)	Deeper penetration (walls, floors, furniture)
Smell	Musty but light	Stronger, earthy, pungent
Typical location	Bathrooms, windowsills, tiles	Walls, ceilings, carpets, insulation, air con
Health risk	Usually low (but can trigger allergies)	Higher — potential to cause or worsen respiratory issues
Response	Can often be wiped with surface cleaner	May require proper mould cleaner, assessment, or remediation

What is mildew?

If you’ve ever spotted a thin, dusty-looking patch on your shower tiles, bathroom ceiling, or window tracks, there’s a good chance it was mildew. Mildew is a type of fungus, just like mould. Because they’re related and thrive in similar conditions, many people assume they’re the same thing.

So, what exactly is mildew?

Mildew is a type of fungus, specifically belonging to the group of fungi known as Ascomycota, one of the largest phyla in the fungal kingdom. While the term "mildew" is used informally to describe certain surface-level moulds, it most commonly refers to fungal species in the genera Oidium and Erysiphe. These fungi are closely related to moulds but tend to grow in more limited, shallow patterns.

It typically appears in warm, damp, and poorly ventilated areas — places like bathrooms, laundry rooms, kitchens, and windowsills. You would normally find them growing on non-porous surfaces like tile, glass, and metal, and usually stays relatively shallow rather than digging into materials the way mould often does.

It’s often described as looking:

White, grey, or yellowish in colour
Powdery or flat in texture
Easy to wipe away in early stages

You might notice it creeping across the grout between your tiles or appearing on the surface of damp walls or ceilings. Unlike mould, which often grows in clusters or irregular blotches, mildew tends to spread out in more uniform patches.

Why is mildew less serious than mould?

Generally speaking, mildew is less invasive and less harmful than most types of mould. Because it stays on the surface, it’s usually easier to clean and doesn’t pose a major structural or health threat — unless it’s left unchecked for long periods or allowed to spread in a very humid space.

That said, mildew can still cause:

Allergy-like symptoms in sensitive individuals (sneezing, watery eyes, coughing)
Persistent musty odours
Staining on walls, ceilings, or textiles over time

So while it’s not considered dangerous in most cases, it’s still something to address promptly, especially if you’re sensitive to indoor air quality or dealing with ongoing moisture problems.

Why does it show up in so many homes?

The short answer? Moisture plus poor ventilation. In Australia’s climate — where warm, humid weather in summer and condensation in winter are both common — mildew can show up almost anywhere that moisture lingers and airflow is restricted.

Common causes include:

Steamy showers with poor bathroom ventilation
Damp laundry left unwashed or unventilated
Moisture build-up on windows in winter
Unsealed grout or old paint in humid areas

What is mould?

Unlike mildew, which tends to stay on the surface, mould is a deeper, more invasive type of fungus that can grow into porous materials — and if left untreated, it can become more than just a cosmetic issue.

Mould belongs to the fungal division Ascomycota and includes many different species such as Aspergillus, Cladosporium, and the often-feared Stachybotrys chartarum (commonly referred to as black mould). These fungi reproduce through airborne spores, which are invisible to the naked eye and can easily spread through your home — especially in damp, humid, or poorly ventilated spaces.

Where does mould grow?

Mould thrives in places where moisture lingers and airflow is poor. You’ll often find it:

On walls and ceilings, especially in bathrooms or behind furniture
Inside cupboards, wardrobes, or closets near exterior walls
On timber, insulation, carpet, or fabrics
In or around air conditioning systems and vents

Unlike mildew, which wipes off relatively easily, mould tends to dig into surfaces. If you’ve noticed staining, bubbling paint, musty odours, or discolouration that keeps coming back, it may be mould rather than mildew.

Is mould harmful?

While not all moulds are toxic, many can release allergens and irritants into the air. Prolonged exposure may cause or worsen:

Asthma symptoms
Allergic reactions (sneezing, itchy eyes, rashes)
Respiratory issues — especially in children, the elderly, or people with weakened immune systems

Some moulds, particularly Stachybotrys, are known to produce mycotoxins — substances that can be harmful when inhaled in large quantities over time.

Can you clean mould yourself?

Yes — in some cases. If the patch is small (no larger than an A4 sheet of paper), on a non-porous surface, and you’re healthy, you can likely treat it yourself using the right products. We've covered this in more detail in our article on how to clean mould safely and effectively.

However, if the mould keeps coming back, covers a large area, or has soaked into walls, carpets or ceilings, it’s best to get a professional assessment. Not sure when to DIY or call in the pros? We’ve got a helpful guide on who to call for mould problems that breaks it all down.

What causes mould to keep coming back?

Mould is rarely just a surface issue. It’s usually a sign of ongoing moisture problems, like:

Hidden leaks behind walls or under sinks
Condensation from poor insulation or lack of ventilation
High indoor humidity
Water damage or past flooding

If you’ve cleaned mould only to see it return, the root cause likely hasn’t been addressed. Prevention is key — which is why we also recommend checking out our blog on how to prevent mould from coming back, especially after cleaning or during humid months.

How to tell the difference in your home

So you’ve spotted something suspicious — maybe a pale patch in the shower or a darker stain creeping along the ceiling. But how do you know if it’s mildew or mould? Here’s a simple guide to help you figure out which one has taken up residence in your space — and what to do next.

1. Check the colour

Mildew tends to be white, grey, or yellow, especially in its early stages.
Mould is usually darker — commonly green, black, brown, or even blue — and may appear in blotchy or irregular patterns.

2. Feel the texture (if safe to do so)

Mildew is often described as powdery, dry, or flat, and typically sits on the surface of tiles or painted walls.
Mould is usually fuzzy, slimy, or spongy, and may feel damp. It often grows into the surface, not just on top of it.

🛑 Important: If you suspect mould and you're immunocompromised, allergic, or unsure about the safety of touching it, it’s best to leave it alone and consult a professional.

3. Smell the area

Mildew has a mild musty smell, like damp clothes or a stale bathroom.
Mould usually has a stronger, earthier, and more pungent odour — the kind you can often smell even before you see it.

4. Try cleaning it (with care)

If it’s mildew, it will usually wipe away easily with a cloth and a basic surface cleaner or natural vinegar spray.
Mould, on the other hand, may not budge with surface cleaners — and could even come back quickly if you don’t address the root cause.

If it returns after cleaning, spreads quickly, or is in a hidden area (like under carpets or behind walls), you’re probably dealing with mould, not mildew.

5. Look at the location

Mildew tends to show up in moist but well-lit, surface-level places — like shower tiles, windowsills, or bathroom grout.\
Mould often grows in darker, more hidden spaces where moisture builds up: behind furniture, in walls, around insulation, in air vents, or beneath carpet.

Still not sure? Consider testing

If the area smells musty or you're unsure whether it's surface-level mildew or something deeper, a mould test kit can help confirm what you're dealing with. Check out our guide on how to test for mould at home, using Australia’s trusted mould solution brand, SAN-AIR.

What to do depending on what you find

Once you’ve figured out whether you’re dealing with mildew or mould, the next step is knowing how to tackle it safely and effectively.

If it’s mildew

Good news: mildew is usually easy to remove and less likely to require specialist help. Here’s how to deal with it:

✅ Clean it promptly - Use a natural surface spray, or a gentle mould and mildew cleaner. Most mildew wipes away without much effort, especially if it’s on tile, glass, or painted surfaces.

✅ Improve airflow - Open windows, use exhaust fans, or run a dehumidifier to keep the area dry and stop mildew coming back.

✅ Monitor the area - Even after cleaning, keep an eye on the spot for any signs of regrowth. If mildew returns quickly, it may indicate ongoing moisture problems that need attention.

✅ Consider prevention products - If you’ve had repeat issues, products like mould prevention gels or moisture absorbers can help keep surfaces dry.

If it’s mould

Mould requires a bit more caution, as it can spread deeper into surfaces and impact air quality.

✅ Assess the size and location

Small patches (about the size of an A4 sheet or smaller) on hard surfaces can usually be tackled yourself.
Larger areas, or mould on porous materials (like plasterboard, insulation, or carpet), should be treated with care — and you may need professional help.

✅ Wear protective gear

If you decide to clean small areas yourself, wear PPE, like:

Gloves
A P2 mask or respirator
Protective eyewear

This helps limit your exposure to spores.

✅ Use the right cleaning products

Avoid relying on bleach alone — especially on porous surfaces like walls, timber, or grout. While bleach might lighten the stain, it often doesn’t reach the mould spores beneath the surface, which means the problem can return quickly.

Instead, consider using a mould-specific solution that’s designed to target and neutralise spores, not just mask the appearance. Products like the SAN-AIR Mould Removal range offer plant-based, low-tox options that are safe to use around the home and work effectively on a variety of surfaces — making them a smart choice for both treatment and prevention.

✅ Address the cause
Mould almost always comes back if the moisture issue isn’t fixed. Look for:

Leaks in plumbing or roofing
Poor ventilation
Condensation around windows or in bathrooms

✅ Know when to call in help

It’s a good idea to get a professional mould assessment if:

The patch is larger than about 1m²
Mould keeps returning after cleaning
You have health issues that could be worsened by exposure
You can’t identify or fix the moisture source

Check out SAN-AIR cleaning solutions that effectively cleans and prevents mould and mildew growth at Aussie Pharma Direct.

Final thoughts — Know what you’re dealing with

At first glance, mould and mildew might look similar — but as you’ve seen, they’re not the same. And knowing which one you’re dealing with can help you choose the right tools, take the right action, and avoid wasted time or recurring problems.

Mildew is generally surface-level and easier to clean — but still a sign that moisture management needs improvement. Mould, on the other hand, can run deeper, cause more damage, and may even affect your health if left unchecked.

Whether it’s a light dusting on your bathroom tiles or a spreading patch on the ceiling, paying attention to the details — texture, colour, smell, and location — can tell you a lot. And when in doubt, don’t be afraid to test, clean cautiously, or get a professional opinion.

If you’re looking for mould-safe cleaning products, natural prevention options, or tips to control moisture indoors, we have plenty of helpful guides and solutions to support you along the way.

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