Mold vs Mildew: How to Tell the Difference
Mold, mildew, efflorescence — similar looks, different problems. Here's how to tell them apart and which matter.
How they compare
- Mildew — flat, powdery, white/gray; wipes off; low risk surface fungus.
- Mold — fuzzy/slimy, raised, dark; penetrates material; health & structural risk.
- Efflorescence — crystalline, chalky, white; brushes off as powder; a mineral salt (not fungus) that flags moisture.
A quick test
Dab diluted bleach on it: mildew lightens fast; 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 coming back, get an inspection.
FAQ
Mold vs mildew questions
Mildew is a flat, powdery surface growth (white/gray) that wipes off. Mold grows deeper, is fuzzy or slimy and darker, penetrates materials, and carries more health and structural risk.
Generally less so — mostly a surface nuisance, but it still signals excess moisture. Mold penetrates materials and poses bigger risks.
Likely efflorescence — mineral salts left by water moving through masonry, not mold. It brushes off as powder but still flags a moisture issue.
Aurora Mold Guides
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