Mildew is a specific powdery or fuzzy growth that sits on the surface of damp fabric, walls, or plants, and is usually whitish or greyish, though it can turn darker, as with the black mildew that forms on steamy bathroom tiles. Mold is the wider term for fuzzy fungal growth that can appear in many colours and can spread more deeply into what it covers, such as the green mold that spreads through old bread. Because mildew can darken and mold can be any colour too, texture and depth are the better clue: a thin, wipeable surface film is more likely mildew, while a deeper, fuzzier growth is more likely mold.
The core difference
Mildew is a specific, thin, surface-level fungal growth, while mold is the wider term covering fuzzier fungal growths of any colour that can spread deeper into a surface.
- mold — a fuzzy fungal growth that develops on food or damp surfaces: green mold had spread across the old loaf of bread.
- mildew — a powdery or fuzzy fungal growth, usually whitish or greyish, that forms on damp surfaces, fabric, or decaying plants: the bathroom tiles were spotted with black mildew from the constant steam.
How to tell them apart
Colour alone will not settle it, since mildew can darken to black and mold can turn up in almost any shade. The more reliable test is texture and depth: mildew tends to be flatter and thinner, sitting on top of damp fabric, tent canvas, or bathroom tiles rather than growing deep into them, while mold is the broader family name and covers fuzzier growths that can spread down through what they cover, including the mold that ruins bread or works its way through a damp wall cavity.
The words get confused because both thrive in the same damp conditions and both can be verbs: something can mildew in a wet attic, just as something can mold. Note also that mold has an unrelated sense, the container used to shape a liquid or soft substance, such as a heart-shaped chocolate mold.
