Mold vs Mildew: How to Tell the Difference
Mold, mildew, efflorescence — they look similar but they're not the same. Here's how to tell, and which ones actually matter.
| Mildew | Mold | Efflorescence | |
|---|---|---|---|
| Look | Flat, powdery | Fuzzy or slimy, raised | Crystalline, chalky |
| Color | White / gray | Black, green, brown | White / off-white |
| Texture | Wipes off surface | Penetrates material | Brushes off as powder |
| What it is | Surface fungus | Fungus, grows into material | Mineral salt (not fungus) |
| Risk | Low / nuisance | Health & structural | Cosmetic, signals moisture |
A quick test
Dab a little diluted bleach on the spot. If it lightens quickly, it's likely mildew; if it stays dark and comes back, it's likely mold. Efflorescence dissolves in water and feels gritty. None of these belong in a dry, healthy home — each points to moisture.
Either way, find the moisture
Whatever it is, it's telling you water is getting somewhere it shouldn't. If it's fuzzy, dark, spreading, or keeps returning, get an inspection.
Questions, Answered
Mold vs mildew FAQ
Mildew is a surface mold that stays flat and powdery (usually white or gray) and wipes off easily. Mold grows deeper, is often fuzzy or slimy and darker, penetrates materials, and can cause structural and health issues.
Mildew is generally less harmful and mostly a surface nuisance, but it still signals excess moisture. Mold can penetrate materials and pose greater health and structural risks.
That’s often efflorescence — mineral salt deposits left by water moving through masonry, not mold. It brushes off as crystalline powder. It still means moisture you should address.
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