If you've wondered what an ERMI mould test actually shows, and what the results mean for your health, this post walks through a real-life example using lab data from a de-identified Dwellness client.
The key outputs are broken down with plain-English interpretation so you can understand how these scores relate to mould levels in your home and what they might mean for the people living in it.
What Is an ERMI Test?
The Environmental Relative Moldiness Index (ERMI) is a DNA-based test developed by the US Environmental Protection Agency in collaboration with the Department of Housing and Urban Development. It analyses dust collected from your home to identify and quantify 36 mould species using qPCR — a molecular method that detects mould DNA with a high degree of precision.
Unlike traditional air sampling, which captures a snapshot of airborne spores at a single point in time, ERMI analyses settled dust that accumulates over months, providing a more complete historical picture of mould burden in the home.
The 36 species tested are grouped into two categories:
- Group 1 — water-damage indicator moulds, most commonly associated with moisture intrusion and indoor contamination
- Group 2 — common indoor moulds typically found in homes without significant moisture problems
The final ERMI score is calculated by subtracting the Group 2 total from the Group 1 total.
What the Lab Found in This Case
In this client case, the ERMI lab detected elevated DNA counts of multiple Group 1 moulds including Aspergillus penicillioides, Aspergillus versicolor, Chaetomium globosum and Wallemia sebi.
The resulting ERMI score was 13.2, placing this home in the fourth quartile — classified as high relative moldiness. For context:
- The ERMI scale runs from approximately -10 (low) to 20 (high)
- The average home scores around 0
- Scores above 5 are generally considered cause for concern in mould-sensitive individuals
- Epidemiological studies have shown an association between higher ERMI values and increased risk of asthma and asthma-related symptoms
Why ERMI Alone Is Not Enough: The HERTSMI-2
ERMI gives a broad picture of overall mould DNA burden. But when a client is chronically unwell or has been diagnosed with Chronic Inflammatory Response Syndrome (CIRS), the HERTSMI-2 score is also calculated from the same data.
HERTSMI-2 focuses on five particularly toxic mould species known to trigger immune dysregulation in sensitive individuals. Each species is weighted according to its risk level, giving a clearer picture of whether the environment is safe for someone with CIRS or mould-related illness.
In this case, the HERTSMI-2 score was 22 — placing it in the high-risk category. As a guide:
- Below 11 — low risk, likely safe for re-entry
- 11 to 15 — borderline, may require further remediation
- Above 15 — high risk for those with CIRS or mould-related illness
What This Means in Practice
This kind of report helps answer questions that are otherwise very difficult to answer:
- Is there hidden mould in this home even though nothing is visible?
- How significant is the exposure, really?
- Is this environment safe for someone with asthma, CIRS or mast cell activation syndrome?
Without a visible water leak or mould patch, a home can still contain dangerous concentrations of mycotoxin-producing mould species trapped in settled dust. Research has found that visual inspection alone fails to detect elevated mould burden in more than half of high-ERMI homes — which is precisely why DNA-based testing adds value where inspections alone fall short.
ERMI and HERTSMI-2 results are most useful when interpreted alongside an in-home inspection and moisture mapping. The numbers tell you what is there. The inspection tells you why.
Book a free consultation to discuss whether ERMI testing is the right next step for your home.