Mold vs Mildew: How to Tell the Difference
Mold, mildew, efflorescence — similar at a glance, different problems. Here's how to tell them apart and which matter.
| Mildew | Mold | Efflorescence | |
|---|---|---|---|
| Look | Flat, powdery | Fuzzy/slimy, raised | Crystalline, chalky |
| Color | White / gray | Black, green, brown | White |
| Texture | Wipes off | Penetrates material | Brushes off as powder |
| What it is | Surface fungus | Fungus into material | Mineral salt (not fungus) |
| Risk | Low | Health & structural | Cosmetic, flags moisture |
A quick test
Dab diluted bleach on it: mildew lightens quickly; mold stays dark and returns. Efflorescence dissolves in water and feels gritty. None belong in a dry, healthy home — each points to moisture.
Either way, chase the moisture
If it's fuzzy, dark, spreading, or keeps returning, get an inspection.
FAQ
Mold vs mildew questions
Mildew is a flat, powdery surface growth (white/gray) that wipes away. Mold grows deeper, looks fuzzy or slimy and darker, penetrates materials, and carries more health and structural risk.
Generally less so — mostly a surface nuisance, though it still signals excess moisture. Mold penetrates materials and poses bigger risks.
Most likely efflorescence — mineral salts left as water moves through masonry, not mold. It brushes off as powder but still flags moisture.
Loveland Mold Guides
More mold resources
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