What CDPH says
The California Department of Public Health is unusually direct about testing (CDPH):
- If you can see or smell mold or moisture, you don't need to measure the amount or identify the type. Testing doesn't give more useful information.
- Measuring mold doesn't tell you whether there's a health problem. There are no recommended "unhealthy levels" for spore counts or particular molds.
- Most experienced investigators rarely test. They look for moisture and its source.
- CDPH doesn't recommend DIY surface and air sampling kits.
- No mold test can show when remediation has succeeded. The best indicator is that the moisture source is fixed, damaged materials are cleaned or removed, and what's left is dry with no visible mold or mold odor.
When testing can help
CDPH notes that in some cases testing may identify hidden moisture that isn't obvious. Other situations where people order testing include real estate transactions, legal disputes, or when a remediation contract calls for it. If someone recommends testing, ask:
- What question will this test answer?
- How will the result change what we do?
- What will it cost, and who interprets it?
Better places to spend money
- A thorough mold inspection focused on moisture.
- Fixing the leak, drainage or ventilation problem.
- Proper mold remediation of what's already growing.
Want a local pro to take a look?It's free for homeowners and there's no obligation.
About "black mold"
CDPH says you don't need to know whether mold is "toxic" or "black." Any mold you see or smell is a risk and should be fixed, and there's no current evidence the particular kind matters.
Want a professional opinion? Request an inspection.
Where we connect homeowners
- Mold removal in Santa Rosa
- Mold removal in Petaluma
- Mold removal in Rohnert Park & Cotati
- Mold removal in Windsor
- Mold removal in Healdsburg
- Mold removal in Sebastopol
- Mold removal in Sonoma
- Mold removal in Glen Ellen & Kenwood
- Mold removal in Cloverdale
- Mold removal in Guerneville & the lower Russian River
- Mold removal in Forestville
Other services
Dealing with this right now?Tell us what's happening and we'll connect you with an independent local provider.
Sources
Sources checked October 18, 2026.
Frequently asked questions
Are home mold test kits worth it?
CDPH doesn't recommend them. If you see or smell mold, a test won't tell you anything you need to act on.
My test says indoor levels are higher than outdoor. What does that mean?
CDPH says the idea that higher indoor levels prove indoor growth hasn't been scientifically proven, and levels vary widely over time. Focus on finding moisture and visible growth.