ERMI Test: What It Is, How It Works, and What Your Score Means
The ERMI test analyzes settled dust from your home using DNA technology to identify 36 mold species. It is far more accurate than air sampling. The related HERTSMI-2 score, created by leading mold illness researchers, focuses on the 5 most dangerous species. A HERTSMI-2 score below 11 is considered safe. The average US home scores about 30. Test kits cost $150 to $300.
What is the ERMI test?
ERMI stands for Environmental Relative Moldiness Index. It was developed by the EPA's Office of Research and Development and uses a laboratory technique called MSQPCR (Mold Specific Quantitative Polymerase Chain Reaction) to identify mold species by their DNA in settled dust.
Unlike air sampling, which only captures mold spores floating at the exact moment the sample is taken, ERMI analyzes dust that has settled over weeks or months. This gives a time integrated picture of what mold species are present and in what quantities. All 6 mold experts in our research synthesis agree that dust based DNA testing is superior to air sampling for detecting hidden mold problems.
The test identifies 36 mold species divided into two groups. Group 1 includes 26 species associated with water damaged buildings. Group 2 includes 10 common outdoor species found in all homes. The ERMI score is the difference between Group 1 and Group 2 levels. A high score means your home has significantly more water damage related mold than normal background levels.
HERTSMI-2: the score that matters most
Leading mold illness researchers, the physicians who defined Chronic Inflammatory Response Syndrome (CIRS), developed the HERTSMI-2 scoring system as a more focused and clinically useful version of ERMI. While ERMI looks at 36 species, HERTSMI-2 focuses on just 5 of the most dangerous mold species found in water damaged buildings:
Aspergillus penicillioides: A common indoor mold that thrives in low moisture environments. Can colonize dust and HVAC systems.
Aspergillus versicolor: Produces sterigmatocystin, a carcinogenic mycotoxin. Common on damp drywall and wallpaper.
Chaetomium globosum: Produces chaetoglobosins. Found on wet drywall, wallpaper, and baseboards. Often found alongside Stachybotrys.
Stachybotrys chartarum: The infamous "black mold." Produces trichothecenes and satratoxins, some of the most potent mycotoxins known. Requires chronically wet cellulose (drywall, cardboard, wood) to grow.
Wallemia sebi: A xerophilic (dry loving) mold that indicates chronic moisture problems. Often overlooked but clinically significant.
Scoring: Each species gets a score of 0, 2, 4, 6, 8, or 10 based on concentration. The 5 scores are added together. Below 11 is considered safe for re-occupancy after remediation. The average US home scores around 30. A score above 15 in a home with sick occupants is clinically significant. Remediation science experts emphasize that individual species data matters more than the composite score because certain species (like Stachybotrys) are dangerous at any concentration.
How to collect an ERMI dust sample
Step 1: Order a kit. EnviroBiomics (envirobiomics.com) and Mycometrics (mycometrics.com) are the two most used labs. Kits cost $150 to $300 and include a Swiffer cloth and collection instructions.
Step 2: Collect dust from the right locations. The standard method is to Swiffer a 6 foot by 3 foot area of carpet or floor in the main living area and the bedroom. The idea is to collect settled dust from areas where you spend the most time. Do not vacuum the area for at least a week before sampling so dust has time to accumulate.
Step 3: Avoid contamination. Wear clean gloves. Do not touch the Swiffer cloth with bare hands. Do not sneeze on it. Place the cloth in the provided bag and seal it immediately after collection.
Step 4: Mail to the lab. Results arrive in 7 to 10 business days. You will receive a report listing all 36 species with concentration levels, your ERMI score, and enough data to calculate your HERTSMI-2 score. Some labs calculate HERTSMI-2 for you; others provide the raw species data and you calculate it yourself.
Pro tip: Take samples from multiple rooms if you want to identify the source. A high HERTSMI-2 score in the bedroom but normal in the living room points to a moisture problem near the bedroom. Remediation science experts recommend looking at individual species data rather than just the composite score because the species tell you what type of water damage is occurring.
ERMI vs air sampling vs The Dust Test
Air sampling: Captures spores floating in the air at one moment. Cheap ($150 to $300 per session) but unreliable. If the air is still, or if mold is behind a wall, spores may not be airborne at the time of sampling. All experts in our research agree: air sampling alone is insufficient.
ERMI/HERTSMI-2: The gold standard for identifying mold species and their concentration. Uses DNA analysis of settled dust. More accurate than air sampling because it captures what has been happening over weeks, not just one moment. Best for determining if a building is safe for a CIRS patient.
The Dust Test (thedusttest.com): A newer, more affordable dust test created with input from remediation science experts. It analyzes settled dust for mold species, mycotoxins, and bacteria. It provides species level data similar to ERMI but adds mycotoxin detection. It is becoming the preferred screening tool for remediation professionals because it shows both what mold is present and what toxins it is producing.
Bottom line: For homeowners screening for a potential problem, The Dust Test or a basic ERMI is sufficient. For CIRS patients or post remediation clearance testing, ERMI with HERTSMI-2 scoring is the standard. Always pair environmental testing with a visual inspection by a qualified mold inspector.
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Get Early AccessFrequently Asked Questions
What is an ERMI test?
ERMI stands for Environmental Relative Moldiness Index. It is a DNA based dust test developed by the EPA that identifies 36 mold species and their concentration in your home. Unlike air sampling, which only captures what is floating at that moment, ERMI tests settled dust that has accumulated over weeks or months. This gives a much more accurate picture of your home's overall mold burden.
What is a good ERMI score?
ERMI scores range from about negative 10 to positive 20 or higher. A score below 2 is considered low mold burden. A score between 2 and 5 is moderate. Above 5 indicates elevated mold levels. However, most mold experts prefer the HERTSMI-2 scoring system, which focuses on the 5 most dangerous mold species. A HERTSMI-2 score below 11 is considered safe for reentry after remediation.
What is HERTSMI-2 and how is it different from ERMI?
HERTSMI-2 was created by leading mold illness researchers. It uses data from the same ERMI dust sample but only scores 5 of the most dangerous mold species: Aspergillus penicillioides, Aspergillus versicolor, Chaetomium globosum, Stachybotrys chartarum, and Wallemia sebi. A HERTSMI-2 score below 11 is the standard for safe re-occupancy after mold remediation.
Where do I buy an ERMI test kit?
ERMI test kits are available from EnviroBiomics (envirobiomics.com) and Mycometrics (mycometrics.com). The kit costs 150 to 300 dollars. You collect a dust sample using the included Swiffer cloth, following specific instructions for where and how to sample. Mail the cloth to the lab and results arrive in 7 to 10 business days. Some mold inspectors include ERMI testing as part of their inspection package.
