Appearance
Mildew is typically flat, powdery or fluffy, and white or gray. It usually grows on the surface of damp areas (e.g., shower tiles, windowsills).
Mold can be fuzzy or slimy and appears in many colors—black, green, brown, or other shades. It often grows deeper into materials (e.g., drywall, grout) and can spread.
If you are unsure which you have, treat visible growth seriously: clean small surface growth and fix the moisture source; get professional help for larger or persistent growth.
Where it grows
Both mold and mildew thrive in moist environments. Mildew is often found on shower walls, windowsills, and other damp surfaces that are easy to wipe. Mold can grow in the same places and also in hidden or porous materials—behind walls, in insulation, under flooring—when moisture is present. Any ongoing moisture (leak, condensation, high humidity) can support either.
Typical severity
Mildew is usually considered less severe: it often stays on the surface and can be cleaned with appropriate products and ventilation. Mold can be more concerning because it may penetrate materials, spread, and affect air quality; some people are sensitive to mold spores. Addressing the moisture source is important for both so growth does not return.
When to call a pro
Call a professional when:
- Growth is widespread or in HVAC or ductwork.
- You cannot safely remove it or are unsure what it is.
- Cleaning does not fix it or it keeps coming back.
- You want a written scope and quote for remediation.
For cost and scope of mold remediation, see our mold remediation cost guide.
Summary comparison
| | Mildew | Mold | |--|--------|------| | Look | Flat, powdery, white/gray | Fuzzy or slimy, many colors | | Where | Often on surfaces (tiles, sills) | Surfaces and inside materials | | Severity | Usually surface-only; easier to clean | Can penetrate; often bigger concern | | Action | Clean and fix moisture | Clean small areas; pro for large or hidden |
Both need the moisture source fixed so growth does not return. When in doubt or when growth is large or recurring, get professional help.
Frequently Asked Questions
What is the difference between mold and mildew?
Mildew is typically flat, powdery or fluffy, and white or gray; it often grows on surfaces. Mold can be fuzzy or slimy, and appears in many colors (black, green, etc.); it can grow deeper into materials.
Is mildew less serious than mold?
Mildew is usually easier to clean and often stays on the surface. Mold can penetrate materials and spread; it is often a bigger concern for both the structure and, for some people, health.
When should I call a professional for mold or mildew?
Call a pro when growth is widespread, in HVAC, or you cannot safely remove it. If you are unsure whether it is mold or mildew, or if cleaning does not fix it, a professional assessment can help.
Where do mold and mildew typically grow?
Both like moisture. Mildew often appears on shower walls, windowsills, and other damp surfaces. Mold can grow there too, plus on drywall, insulation, and other materials when moisture is present.