ERMI stands for Environmental Relative Moldiness Index. It's a DNA-based test on settled house dust that gives you a single score — usually between roughly -10 and +20.
How it works
You collect dust from a few rooms with a special swab kit, mail it to a lab, and the lab runs PCR (genetic testing) on 36 mold species. The result is a relative score that compares your home to a reference set of US homes.
What the score is good for
- A high relative score (especially with certain water-damage species like Stachybotrys, Chaetomium, or Aspergillus penicillioides) is a strong signal that water damage has occurred and is worth investigating.
- A trend over time — testing before and after remediation — gives you objective evidence about whether work was effective.
What the score doesn't tell you
- It does not tell you where in the building the mold is.
- It does not tell you whether you personally will react to the property.
- It does not replace a physical inspection by someone who knows what to look for.
Pairing ERMI with other tools
Most people who use ERMI seriously also pair it with:
- A visual inspection by an inspector who specializes in mold
- HERTSMI-2, a related score derived from ERMI focused on the most water-damage-correlated species
- Air sampling if a specific room is suspected
Where to get tested
We list ERMI providers on the testing services page. Some links are affiliate links — if you book through them we may earn a small commission, which keeps this platform free. Listing a provider is informational and not an endorsement.