Mould vs Mildew: What’s the Difference and Does It Matter?

People use “mould” and “mildew” interchangeably, but they’re actually different organisms with different risk levels. Understanding the difference helps you decide whether you need a spray bottle or a professional inspector.

Mildew: Surface-Level Problem

Mildew is a surface fungus that grows flat against materials. It appears as grey, white, or yellowish patches — typically on bathroom tiles, shower curtains, or damp fabrics. Mildew is generally easier to clean and less likely to cause serious structural damage.

Mould: The Deeper Threat

Mould penetrates into materials — wood, plasterboard, carpet — and sends root-like structures (hyphae) deep into porous surfaces. This is why wall mould and ceiling mould often return after surface cleaning. Species like Stachybotrys (black mould) can cause serious health problems.

When Does the Difference Matter?

If you can wipe it away and it doesn’t return — it was likely mildew. If it’s penetrated the material, keeps coming back, covers a large area, or you can smell it behind walls — it’s mould, and you need professional help. In Adelaide’s climate, what starts as mildew often progresses to mould during the winter condensation season.

Assess your home’s mould risk to understand where you stand.