Mildew and mould are both fungi, and in everyday Australian use the words overlap. The useful distinction is depth: mildew is light growth that sits on the surface and wipes away, while mould grows into the material and comes back until the moisture feeding it is fixed. Whether it stays gone after a firm clean tells you more than its colour does.
The working difference
NSW Health describes mould as part of the fungi family, present almost everywhere, that grows indoors in wet or moist areas lacking ventilation. “Mildew” is the everyday word people use for the lighter, flatter end of that growth.
- Mildew tends to be flat or powdery and stays on the surface. It often starts white, grey or yellowish and darkens with age. It’s typical on fabric, shower curtains, leather, paper and window sills, where there’s steady low-level damp.
- Mould covers a wider range of growth. It is often darker and fuzzier, and more likely to have grown into a porous material such as plasterboard, timber, grout or carpet.
You don’t need a lab to make the call that matters, which is whether the growth is superficial or embedded.
How to tell them apart at home
| Sign | Points to mildew | Points to mould |
|---|---|---|
| Texture | Flat or powdery | Fuzzy, slimy or raised |
| Where | Fabric, shower curtains, sills, leather | Plasterboard, ceilings, timber, grout, carpet, cavities |
| After a firm wipe | Comes off and stays off | Leaves a shadow, or returns |
| Smell | Mild mustiness | Stronger, especially from enclosed spaces |
No single sign is decisive, and colour is the least reliable of all. The best test is simple: clean it, dry it, and watch. If it doesn’t return, it was surface growth. If it comes back, especially on a porous surface, treat it as mould whatever it looked like.
Where each shows up in Illawarra homes
- Shower curtains, bath mats and fabric: usually mildew. A wash, or a replacement, and better drying fixes it.
- Bathroom ceilings and cornices: where the line blurs fastest. Light spotting from steam on a cold ceiling can, left through a winter, grow into the paint film and the plasterboard behind it. That progression is what bathroom and ceiling mould removal deals with.
- South-facing bedroom walls and behind wardrobes, common in double-brick homes: condensation mould that returns until airflow changes.
- Window frames and sills in tightly sealed newer homes around Shellharbour, Shell Cove and Flinders: starts as surface growth from condensation and spreads if habits don’t change.
- Subfloors and roof voids in older raised-floor homes: almost always mould by the time anyone notices, because the smell arrives well after growth has established in timber or insulation.
Does it matter which one it is?
Less than people expect. The response is the same: find what’s making it damp, then clean or remove the growth. What changes is the scale.
A DIY job when it’s light, on a hard or washable surface, first time, and the cause is obvious: a curtain that never dries, a sill that fogs every morning. NSW Health recommends mild detergent or diluted vinegar for routine clean-up and drying the surface completely; the bleach vs vinegar guide covers the details.
Get a professional opinion, whatever you call it, when:
- It covers more than a small patch or shows up in several places
- It’s growing into plasterboard, timber, carpet or insulation
- It returns after cleaning
- There’s a musty smell with nothing visible, which often means a subfloor or roof void (see the musty smell guide)
- It followed a leak, storm or flood
A mould inspection and moisture investigation settles it with moisture meters and, where useful, thermal imaging. The mould removal vs remediation guide explains what changes once it’s a professional job. A couple of clear photos and your suburb through the quote form is a good start; your enquiry goes to an independent local contractor, who quotes in their own name.
Frequently asked questions
Is mildew a type of mould?
Both are fungi, and in casual Australian use the words are often swapped. The difference that matters at home is behaviour: growth that sits on the surface and wipes away, versus growth that has grown into the material and keeps returning.
Can mildew turn into a bigger mould problem?
Left on a damp surface with nothing changed, light surface growth can establish more deeply, especially on plasterboard or timber. That’s why “mildew” that keeps coming back is worth treating properly rather than wiping again.
Does bleach get rid of both the same way?
Bleach lightens staining on hard surfaces in both cases, but on porous materials it often doesn’t reach growth below the surface, so the patch greys out and comes back. It also does nothing about the damp causing it.
Should I get an inspection if I think it’s just mildew?
If one firm clean removes it and it stays away, probably not. If it recurs, spreads, or you can’t tell whether it’s on the surface or growing into a wall or ceiling, an inspection is the cheaper path than repeating the wrong fix.
Is a musty smell in my house mildew or mould?
A persistent musty smell with nothing visible more often comes from mould somewhere hidden, such as a subfloor, roof void or behind a wardrobe, than from surface mildew, which you can usually see on the item it’s growing on.