Mold vs Mildew

What the Terms Really Mean

Mildew is not a separate biological category from mold. In common usage, mildew refers to surface-level growth on damp surfaces — the flat gray or white spotting on shower grout, window sills, and fabric.

Mold in everyday usage refers to growth that penetrates material, appears raised or fuzzy, and often signals a structural moisture problem. Both are fungi. The useful distinction is not the organism but whether the growth is on the surface or in the material.

Telling Them Apart in Practice

Mildew is usually flat, powdery, white to gray or light brown, and sits on top of the surface. It wipes off, and the material underneath is intact.

Mold is often raised, fuzzy or slimy, and green, black, or dark blue. It does not fully wipe away, and the material beneath is typically stained, soft, or damaged.

The Test That Actually Matters

Clean the spot. If it comes off completely and the material underneath is solid and dry, you were dealing with surface growth from humidity. Improve the ventilation and it should stay gone.

If it does not come off, if the material is soft or discolored underneath, or if it returns within weeks, you have growth in the material and a water source that has not been addressed.

Why the Distinction Matters

The Katy Context

In this climate, a great deal of what homeowners find is genuine surface growth driven by humidity — bathroom grout, window sills, closet walls on exterior corners. Better ventilation resolves most of it.

The cases that matter are the ones that keep coming back. Recurrence means the moisture is structural, and no amount of cleaning will outpace it.