FAQ
Frequently asked questions.
Common questions about ERMI, HERTSMI-2, dust-based qPCR testing, and how ExplainmyERMI's interpretation service fits with the rest of a mold investigation.
What is an ERMI test?
The Environmental Relative Moldiness Index (ERMI) is a dust-based mold test developed by the EPA. A homeowner collects settled dust from inside the home, sends it to a qualified lab, and the lab measures the DNA of 36 specific mold species. The result includes raw spore-equivalent counts and a single ERMI score that places the home on a scale relative to a national reference distribution.
What does the ERMI score mean?
The ERMI score is calculated by summing the log-transformed concentrations of 26 “water-damage indicator” species (Group 1) and subtracting the sum of 10 “common indoor” species (Group 2). Higher scores indicate a higher mold burden relative to a reference set of U.S. homes. The single score, on its own, can mask very different underlying species patterns, which is why our four-tier classification reads the species composition, not just the ERMI total.
What is HERTSMI-2?
HERTSMI-2 (Health Effects Roster of Type-Specific Formers of Mycotoxins and Inflammagens, version 2) is a derivative scoring system developed by Dr. Ritchie C. Shoemaker. It uses only five of the 36 ERMI species, weighted by their inflammatory and mycotoxin-producing potential, to produce a separate score from the same lab data. Your report includes both ERMI and HERTSMI-2.
What is water activity (Aw) and why does it matter for mold?
Water activity (Aw) is a measurement from 0 (bone dry) to 1.0 (pure water) describing how much usable moisture is available in a material. Different mold species require different amounts. Xerophilic species grow at Aw as low as 0.69 (humid air alone). Mesophilic species require Aw 0.80–0.90 (condensation surfaces). Hydrophilic species require Aw above 0.90 (active liquid water). Knowing the water-activity class of an elevated species helps narrow what kind of moisture problem is involved.
How does an ExplainmyERMI report differ from a mold inspection?
ExplainmyERMI is not a mold inspection or assessment. We do not visit your property, collect samples, or provide remediation advice. We interpret the lab data on a report you already have, explaining what the numbers mean and what kind of moisture conditions the species pattern points to. A licensed mold assessor performs the on-site investigation; this report helps you understand the lab portion of that picture.
Is your ERMI interpretation a funnel to other services you provide?
No. Many ERMI interpretation services are bundled with the test kits, supplements, or remediation work the same company sells next: which creates an incentive to make the report read worse than the data warrants, because a scarier interpretation drives more downstream purchases. ExplainmyERMI sells only the interpretation. We don't offer kits, supplements, remediation, consulting calls, or any other paid follow-on, so there's nothing downstream for us to steer you toward.
Is the ERMI score itself enough?
No, and the EPA explicitly states ERMI was developed for population-level research, not individual-home diagnosis. The score is one summary number across 36 species; the diagnostic detail is in which specific species are elevated, by how much, and what colonizer group they belong to. Our report leads with the Group classification, supports it with the ERMI score and HERTSMI-2, and gives most of its 30+ pages to the species-level read, the Moisture Ladder, and the climate context.
Does the EPA recommend the ERMI test for use in homes?
No. The EPA, which developed ERMI, currently states on its public mold information page that ERMI “is a research tool and is not recommended for use except as a research tool.” ExplainmyERMI does not perform, sell, or recommend the ERMI test, and we do not claim EPA endorsement of the test or of our interpretation of it. If you do not yet have an ERMI result, please read the EPA’s guidance directly at epa.gov/mold before deciding whether to order one from a licensed laboratory. Our service is an educational interpretation of test results you have already obtained from a laboratory you chose. Our methodology page sets out the EPA’s position in the EPA’s own words, with its history and sources.
Why dust testing instead of air sampling?
Air sampling captures intact spores at one moment in time, a snapshot of one slice of the airborne particle load. Dust testing captures everything that has settled in the home over weeks to months: spores, hyphal fragments, and the sub-spore cell-wall fragments that recent research has shown carry most of the bioactive load. Footsteps, vacuuming, and HVAC cycles continuously re-aerosolize dust-bound particles into breathing-zone air, so dust composition is a time-integrated proxy for what people actually inhale. Multiple studies have found that airborne spore counts in mold-problem homes are no higher than in non-problem homes, one of the reasons the EPA chose dust-based qPCR over spore counts when designing the ERMI research instrument.
Read the full dust-vs-air discussion with primary-source citations →
Doesn’t qPCR just detect DNA from dead spores?
It detects dead spores, but not only dead spores. qPCR counts DNA whether it comes from a living spore, a dead spore or a fragment of hyphae. Culture methods miss the dead spores and the fragments entirely. The objection assumes that intact, living spores are the only exposure that matters. The indoor-aerosol research suggests otherwise. In one laboratory study, contaminated surfaces released more fragments than intact spores under every condition tested. For Stachybotrys chartarum, another study counted roughly 500 fragments for every spore. A breathing model in the same study put the fragments’ deposition in the airways at 230 to 250 times that of the spores. Dead spores and fragments still carry allergens. For some species they also carry toxins. An ERMI result is not a fragment count, though. It measures how much of each species has been present in the dust.
How accurate is the ERMI test?
Less precise than a single number suggests. The ERMI’s developers put the standard deviation of any ERMI value at about 3. By their account, a score of 2 is not different from a 1 or a 4 (Vesper et al. 2007). Repeat samples from the same home differ too. In one published cohort (Kamal et al. 2014), 52 paired samples taken 1 to 7 months apart had mean ERMI values of 12.8 and 15.2, and individual homes moved in both directions. The ExplainmyERMI Group is no steadier than the score. When we simulated assay noise of that size on the reference homes, about 31 in 100 landed in a different Group. So read a single result as a band, not a verdict. EPA developed ERMI as a research tool for comparing groups of homes, not for diagnosing a single home. A dust result is a signal built up over weeks to months. It does not replace a direct moisture investigation.