Ask ten people how to test for mold and you'll get ten answers. The truth is that each test answers a different question — and knowing which question you're asking is most of the battle. Here's the honest tour, including the one most of our community starts with.
ERMI — the one we'd start with
ERMI (Environmental Relative Moldiness Index) is a DNA-based test on settled house dust. You collect dust from a few rooms with a swab or cloth kit, mail it to a lab, and the lab runs PCR genetic testing against 36 mold species, producing a single score (usually between about −10 and +20).
Why the community usually starts here:
- Dust is a record, not a snapshot. Settled dust accumulates over months, so ERMI reflects the building's history — including mold that only releases spores intermittently. An air sample can miss what a building did last month; dust doesn't forget as easily.
- It sees the water-damage species. High counts of species like Stachybotrys, Chaetomium, or Aspergillus penicillioides are a strong signal that water damage has occurred somewhere, even if you can't see it.
- It's comparable. Because the panel and scoring are standardized, you can compare before-and-after remediation, or compare a prospective home against the one that made you sick.
- No inspector required. Kits run roughly $150–300 and you collect the sample yourself. Many members in our community use Envirobiomics or Mycometrics.
What ERMI doesn't tell you (this part matters just as much):
- It does not tell you where the mold is. A bad score says "investigate," not "it's under the kitchen sink."
- It does not predict whether you will react to a building. Sensitivities vary enormously.
- It is a relative research index, not a pass/fail safety certificate. The EPA developed it as a research tool, and no score guarantees a building is safe or unsafe.
- It doesn't replace eyes on the building — a skilled inspection can find what any lab number can only hint at.
HERTSMI-2 — the budget re-check
HERTSMI-2 scores just 5 of ERMI's most health-relevant species. It's cheaper, and many practitioners — especially those following the Shoemaker Protocol — use it as a re-occupancy check after remediation ("is this building likely safer now?"). Good for trends and re-checks; less complete than a full ERMI. Some labs report both from the same sample.
Air sampling (spore traps) — the snapshot
An inspector draws a known volume of air through a cassette and a lab counts the spores, usually comparing indoor rooms against an outdoor baseline. It can be useful for comparing rooms or documenting an active problem — but it's a snapshot of one moment. Spore release varies hour to hour, and mold sealed behind a wall may barely show. A clean air sample does not mean a clean building, which is why many in our community have been burned by "the air test was fine."
Tape lifts & surface swabs — "is this spot mold?"
Cheap and direct: press tape to a suspicious spot, and a lab tells you what species it is. Perfect for confirming visible growth. Tells you nothing about the rest of the building.
Settling plates (petri dishes) — the drugstore option
Open dishes that catch whatever falls into them, then grow it. They're inexpensive, but they only detect viable spores heavy enough to settle, and results are easy to misread in both directions. Most serious inspectors don't rely on them — treat a "clean" plate result with real skepticism.
Mold detection dogs — finding the where
Trained dogs can locate hidden mold sources behind walls and under floors — the very thing lab tests can't do. They shine when a test says "there's a problem" and nobody can find it. Pair with testing for confirmation.
Professional inspection — the human element
A mold-literate inspector brings moisture meters, thermal imaging, building-science experience, and the pattern recognition to know where water goes. For a home purchase or a stubborn mystery, this plus an ERMI is the strongest combination we know of.
So which one?
- Overall "is this building okay?" → Start with an ERMI.
- Re-check after remediation, or on a budget → HERTSMI-2.
- Find where it's hiding → Inspector, possibly with a mold dog.
- Confirm a visible spot → Tape lift.
- Air samples → Useful in an inspector's hands for room-to-room comparison; don't let a clean one overrule your symptoms.
Whatever you choose, remember: tests inform judgment, they don't replace it. We're a community sharing what worked for us — not a testing authority — so weigh results with a qualified, mold-literate professional, and trust your own body's signals.
Ready to test? See the community's go-to kits on our Testing page, or find an inspector on Trusted Pros.