Mold vs mildew — at a glance
- Mildew is a surface fungus. Powdery, white or gray, grows on damp surfaces like shower tile, window sills, and bathroom corners. Wipes off easily. Doesn’t usually penetrate the material.
- Mold is a broader category of fungi, many of which do penetrate materials and grow deeper. Fuzzy or slimy texture, varied colors (black, green, yellow, pink, white). Harder to remove.
- In practice: “mildew” in common speech usually means surface mold on bathroom caulk. The clinical word is still mold.
- DIY cleanup rule: under 10 square feet of surface growth with a known fixable moisture source — DIY with soap and water. More than that, or hidden growth, or recurring — call a pro.
- Not sure what you have? Vault’s $99 basic visual inspection or $349 air sampling tells you for certain. (385) 250-2825.
What mildew actually is
Botanically, mildew is a type of mold — but “mildew” is used in two common ways:
- Plant mildew — powdery white fungus on garden plants. Different organism entirely, not an indoor-air concern.
- Household mildew — the surface mold most people deal with in bathrooms. White to gray, powdery, lives on top of the surface rather than growing into it. Common on shower grout, caulk, window sills, and the back of toilet tanks.
Household mildew is relatively harmless to healthy people (allergy sufferers and asthmatics may react). It wipes off with soap and water or a dilute vinegar solution. The permanent fix is to lower humidity: run the bath fan during and after showers, keep bathroom door open afterward, keep towels dry.
What “real” mold looks like
The molds that actually concern restoration pros are species that penetrate porous materials and grow” into them:
- Stachybotrys chartarum — the “toxic black mold” of the news cycle. Dark, slimy, grows on cellulose (drywall paper, wood, cardboard).
- Cladosporium — olive-green to black, common outdoor and indoor mold. Many species.
- Aspergillus — grows in a huge range of indoor conditions. Can produce mycotoxins.
- Penicillium — blue-green, fast-growing on water-damaged materials.
- Alternaria — black, often outdoor; indoors it’s a sign of water intrusion.
You cannot identify the species by looking. Point: if what you see is on drywall, wood, carpet, insulation, or a porous surface — treat it as a real-mold problem, not a mildew wipe-down.
The practical difference (that matters for homeowners)
| If you see… | It’s probably… | What to do |
|---|---|---|
| Powdery white or gray film on shower caulk, grout, or tile | Mildew (surface mold) | DIY cleanup; fix the humidity source |
| Fuzzy black patches on drywall or wood | Real mold | Call a pro; don’t disturb |
| Darkening along the bottom edge of a wall | Hidden water damage + mold | Call a pro |
| Musty smell with no visible growth | Hidden mold | Call a pro — air sampling helps locate |
| Growth on a vinyl shower curtain or liner | Mildew | Replace the liner; clean the shower |
| Mold around a window with condensation | Mildew if just on sill, real mold if into frame | Investigate; may be ventilation issue |
Why bleach is a bad DIY choice (mostly)
Bleach kills mold on nonporous surfaces (tile, glass, metal) but it doesn’t effectively kill mold that has grown INTO porous surfaces (drywall paper, wood, grout). The bleach lightens the stain, so the mold looks gone — but the living growth underneath is still there, and it comes back.
Also: bleach releases chlorine fumes that are harder on lungs than the mold itself. Use dish soap and warm water on real mildew. Use nothing — just call a pro — on real mold.
When to just call us
- Visible growth over 10 square feet (EPA guidance)
- Growth after a known water event (burst pipe, roof leak, flood)
- Musty smell that doesn’t go away with cleaning
- Growth that returns within weeks after a cleaning
- Growth you can see spreading
- Anyone in the home with asthma, allergies, immune issues, or respiratory conditions
Not sure if it’s mildew or something worse?
Call (385) 250-2825. Mold inspection: $99 basic visual, $199 with moisture + thermal, $349 with air sampling and Sporecyte lab analysis.
Mold remediation · Mold health effects · Containment process · DIY vs call a pro
Also see: Found black mold? What to do · Mold in your bathroom
More guides: Mold on drywall · Does bleach kill mold?
Need help with mold in Provo? Our Provo mold remediation crew is AMRT-certified, and remediation jobs start at $500. Call (385) 250-2825.