How to read an ERMI report without panicking
The ERMI score is not the story. The species are. Here is how to read the dust sample result and what to do with it.
Clients send me ERMI results almost weekly. The first thing I do is tell them to stop looking at the score. The score is the least useful part of the report.
What ERMI actually is
ERMI stands for Environmental Relative Moldiness Index. The EPA developed it in the early 2000s as a research instrument to compare the mold load of homes against a baseline. The baseline was the 2006 HUD American Healthy Home Survey, which analyzed dust samples from 1,096 homes across the US. Your home’s score is a ratio of your mold profile against those 1,096 reference homes.
The score was never intended as a retail diagnostic. Somewhere around 2012 a cottage industry of functional medicine practitioners started ordering ERMIs for patients, and the score became a pass-fail signal. It was not designed for that job, and it fails at it regularly.
Why the score is misleading
The ERMI score runs from roughly -10 to +30. Most consumer lab reports mark scores above +2 as “elevated” and above +10 as “high.” Here’s the problem: the score weights all 36 species equally, adjusted for the reference population. It doesn’t distinguish between a Cladosporium spike (an outdoor mold that blew in through the front door) and an Aspergillus versicolor spike (an indoor mold that produces mycotoxins including sterigmatocystin).
Two homes can have the same ERMI score of +4. One home has the score because of outdoor-air infiltration and no active water intrusion. The other has the score because of a hidden colony behind a bathroom wall. The number is the same. The response should not be.
The species list is the story. The score is just an attention-grabbing headline.
The species are the story
Every ERMI report lists 36 species grouped into two categories. Group 1 contains 26 species associated with water-damaged buildings. Group 2 contains 10 common outdoor species. The ratio of Group 1 to Group 2, plus which specific species appear at what counts, can give you an idea of what could be happening.
Group 1 species to watch for
- Aspergillus versicolor · produces sterigmatocystin, a mycotoxin with demonstrated health effects. Finding this one at any meaningful count warrants investigation.
- Stachybotrys chartarum · the “black mold” of headlines. Indicates chronic water damage. If present, visual inspection is the right next step, not another ERMI.
- Chaetomium globosum · grows on water-damaged cellulose materials (drywall paper, wood, paper). Often appears alongside Stachybotrys.
- Aspergillus niger, flavus, penicillioides, ochraceus · each has its own health profile. Penicillioides in particular is a marker of chronic dampness that the homeowner may not have noticed.
- Wallemia sebi · tolerates low-moisture environments, grows on dust in HVAC systems. Often the first species to show when a home has a ventilation problem.
Group 2 species for context
- Cladosporium species · common outdoor molds that drift in with outside air. High counts here without Group 1 elevation suggest an air infiltration issue, not an indoor colony.
- Alternaria alternata · another outdoor mold. major allergenic effects but not a water damage indicator on its own.
In the last 60 ERMI reports I’ve reviewed, the “worst” score was +38 on a Tampa home. Species breakdown: primarily Cladosporium and Alternaria, almost no Group 1. The finding: aggressive outdoor air infiltration around old window frames. Fix was window weatherstripping, not remediation.
How to read your own report
When you get an ERMI result, skip to the species list before you look at the score. Walk through it in this order.
- Are any Group 1 species present at meaningful counts? (Q3+ for most species)
- Is Aspergillus versicolor on the list at any count? (this one matters even at low levels)
- Is Stachybotrys or Chaetomium present? (skip the next ERMI and get a visual inspection)
- What’s driving the score? (Group 1 or Group 2?)
- Does the profile match your symptoms? (specific species have specific health associations; you might also have health labs to match it to)
Want help reading your ERMI?
A 40-minute virtual consult reviews your report in context, with your symptoms, your home, and your history for only $195.
When to order a custom panel
The standard ERMI panel tests 36 species. If you have urine mycotoxin results already, a custom ERMI panel matched to your specific mycotoxins is more useful than another standard one.
Use code HHZONE at Envirobiomics for a 10 percent discount, and email Deb before you order, so we can suggest the right panel.
The ERMI can be a useful screening tool when you read it correctly. Read it wrong and it’s a source of panic. Read it right and it’s the starting point for a targeted conversation about what’s actually going on in your home.
Ready when you are.
Book an inspection, schedule a virtual consult, or request more information. Deb handles the scheduling so there’s a human at the other end of the phone.