What Is an ERMI Mold Test and What Does Your Score Mean?

The ERMI test analyzes settled dust from your home to measure the DNA of 36 mold species and assign your home a single score. Use this guide to understand where your number falls and what the individual species results are telling you.

What Is the ERMI and Where Does It Come From?

ERMI stands for Environmental Relative Moldiness Index. The EPA developed it because existing mold tests were inconsistent and hard to compare between homes. By standardizing the sample method and testing against a fixed database, the ERMI gives you a number you can actually place in context.

The test uses a technology called mold-specific quantitative polymerase chain reaction (MSqPCR). In plain terms, it extracts DNA from the dust in your home and identifies which mold species are present and at what concentration. Dust accumulates over time, so the ERMI reflects weeks or months of mold history, not just one afternoon.

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It’s worth noting that EPA itself describes ERMI as a research tool and does not formally recommend it for assessing individual homes. That said, it is widely used by environmental physicians, industrial hygienists, and mold inspectors as one part of a broader assessment.

How Samples Are Collected

You vacuum about two square meters of carpet or floor in either your living room and/or master bedroom, using a special canister that captures the dust. The canister gets mailed to a certified lab, and results come back within a few days. You can order an at-home kit yourself, or an inspector or doctor can collect the sample during a visit. Most labs charge between $150 and $300 for the analysis. There are lots of options including EnviroBiomics and ImmuniLytics being some of the most popular

How to Interpret Your Score

Scores generally fall between -10 and +20, though outliers are possible. For people with mold sensitivity or CIRS, some physicians recommend targeting an ERMI of 2 or lower. For the general population, under 5 is commonly considered acceptable.
Here is what ERMI results typically look like:
Score: -10 to 0
What it generally indicates

Low mold burden, consistent with a clean home.

Recommended next step

No action needed.

Score: 0 to +2
What it generally indicates

Borderline, worth monitoring.

Recommended next step

Investigate moisture sources.

Score: +2 to +5
What it generally indicates

Elevated, suggests past or current water damage.

Recommended next step

Professional inspection recommended

Score: +5 to +10
What it generally indicates

Significant contamination.

Recommended next step

Remediation likely needed.

Score: Above +10
What it generally indicates

Serious problem.

Recommended next step

Immediate action recommended.

SPECIES MATTER MORE THAN THE NUMBER

The Score Is Only Half the Picture

The number matters, but the species breakdown matters more. A score of +4 with common outdoor molds driving it is a different situation from a score of +4 with Stachybotrys chartarum present. Stachybotrys is heavy, sticky, and hard to aerosolize. Catching even one spore in a dust sample is a serious finding, regardless of what the overall score says.

The five species below are also the basis of the HERTSMI-2, a shorter test some doctors use when evaluating patients for mold-related illness. If you have an ERMI report, you already have the data to calculate a HERTSMI-2 score from it.

Any species marked in the highest concentration quartile (Q4) in your report should be investigated, regardless of your overall ERMI number.

KEY GROUP 1 SPECIES TO WATCH

Stachybotrys chartarum

Toxic at any level. One spore is a red flag regardless of overall score.

Chaetomium globosum

Associated with water damage and mycotoxin production. Should not be present in a healthy home.

Aspergillus versicolor

Produces sterigmatocystin, a mycotoxin linked to chronic illness. Common in water-damaged materials.

Aspergillus penicillioides

Thrives in sustained high-humidity environments. Elevated counts suggest ongoing moisture problems.

Wallemia sebi

Found in very dry, salty conditions. Its presence is unusual and warrants further investigation.

What the ERMI Does and Does Not Tell You

What it tells you

The historical mold burden in your home, identified down to species level.

How your home compares to a national database of over 1,000 U.S. households.

Useful objective data for doctors investigating chronic health symptoms.

A baseline record for homebuyers who want to know a property's mold history.

What it does not tell you

Where the mold is. A high score tells you something is wrong, not which wall or room.

Current airborne spore levels. Dust-based testing reflects history, not what is in the air right now.

Whether mold is currently active. Past damage that has been fixed can still show a high score.

Whether remediation worked or if any of the spores are viable or culturable mold.

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