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What Spore Counts Mean
Air sampling reports list spores per cubic meter, but the number alone does not define risk. Mold is everywhere, and normal indoor air often contains spores similar to outdoor air.
What Counts Cannot Tell You
Short term air samples cannot predict health effects for a specific person. Public health agencies emphasize that visual inspection and moisture investigation are more reliable than a single air test.
- No federal health threshold exists for mold spores
- Counts do not prove where mold is growing
- Short sampling windows miss daily variability
- Moisture sources are the real root cause
Using Comparison Samples
- Collect concurrent outdoor samples when the written air-sampling protocol calls for an indoor/outdoor comparison
- Compare types and concentrations only within the selected method’s limitations
- Use indoor/outdoor differences as investigation clues, not health or safety thresholds
- Document weather, HVAC operation, activity, location, and sample duration
Species Patterns Are Clues
Common Outdoor Molds
- Cladosporium and other common genera appear on most reports
- See common indoor molds for examples
Moisture-Associated Clues
- Some genera may guide inspection toward persistently damp materials
- No named genus, count, or indoor/outdoor ratio alone proves the source, extent, duration, or health risk
Context Factors
- 1
HVAC status
Running or off changes particle movement and counts.
- 2
Recent cleaning
Vacuuming and dusting can temporarily raise counts.
- 3
Sampling location
Samples near returns or windows can skew results.
Questions to Ask
- Which controls or comparison samples did the written protocol require?
- How did you interpret the indoor to outdoor comparison?
- Were samples taken near visible damage or complaints?
- Does the report recommend next steps?