The phrase 'black mold' is doing a lot of work
When most homeowners say 'black mold' they mean Stachybotrys chartarum, the dark-greenish-black species that drew the headlines in the late 1990s and still drives most of the fear-based marketing in this category. Here's what's true and what's not.
What Stachybotrys actually does
Stachybotrys grows on cellulose materials that have been wet for an extended period. Drywall paper, gypsum board backing, cardboard, water-damaged wood. It produces mycotoxins (specifically trichothecenes) and can trigger respiratory symptoms in sensitive individuals.
It is not the only mold that produces mycotoxins. Aspergillus, Penicillium, and Fusarium all produce their own mycotoxins. Some are arguably worse for sensitive populations than Stachybotrys.
Why species ID matters less than you think
In our experience running thousands of samples through accredited labs, the single most predictive factor for "does this house need remediation" is total spore count per cubic meter compared to an outdoor control sample. Not species.
A house with 5,000 spores/m³ of Cladosporium (often dismissed as 'just outdoor mold') indoors and 200 spores/m³ of Cladosporium outdoors has a problem. A house with 50 spores/m³ of Stachybotrys indoors with no source visible on a thorough inspection might not.
The exception: if Stachybotrys, Chaetomium, or Memnoniella shows up at all in an air sample, that's a flag we take seriously. Those three are 'water damage indicators' that almost never appear without sustained moisture intrusion behind a wall or under a floor.
What 'black mold' often actually is
When a homeowner shows us a 'black mold' spot, in our experience it's most often:
| What it actually is | Frequency we see it |
|---|---|
| Cladosporium (very common outdoor + indoor mold) | ~40% |
| Mineral efflorescence (calcium / salt deposit, not mold) | ~20% |
| Penicillium / Aspergillus mix | ~15% |
| Mildew (a different category of fungi) | ~10% |
| Black soot from a candle / cooking / cigarettes | ~5% |
| Actual Stachybotrys chartarum | ~10% |
Looking at a photo, we can sometimes narrow it down but never confirm. The only honest answer is a surface tape lift or an air sample.
What to do next
If you're staring at a dark spot and wondering what it is:
- Don't touch it bare-handed.
- Take three or four photos at different angles, including one wide shot showing the surrounding area.
- Send them at moldremovalandtesting.com/photo-check. We reply within 2 business hours with what it likely is and whether testing is warranted.
The species name matters far less than the answer to two questions: Is moisture present? and Is spore count elevated above outdoor baseline? If yes to both, we remediate regardless of species. If no to both, we usually don't.