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ERMI and HERTSMI: Dust Testing for Mold

These DNA-based tests analyze settled dust for mold species. Useful in some contexts, but not recommended by EPA for routine decision-making.

What is ERMI?

ERMI (Environmental Relative Moldiness Index) is a DNA-based dust test developed by the U.S. EPA as a research tool. It analyzes settled dust for specific mold species and produces a score intended for comparing groups of homes in studies, not diagnosing individual buildings.

What ERMI Measures

ERMI measures mold DNA in dust. That means it detects both living and dead mold and may reflect past conditions rather than current active growth. It does not identify the moisture source or explain why mold is present. The test can detect a wide range of species, including common indoor molds and water-damage indicators like Stachybotrys and Chaetomium.

What ERMI Detects

  • 36 different mold species via DNA
  • Both living and dead mold spores
  • Historical contamination in dust
  • Water-damage indicator species

What ERMI Cannot Do

  • Identify the moisture source
  • Distinguish current vs. past contamination
  • Measure airborne exposure levels
  • Provide a definitive health risk assessment

What is HERTSMI-2?

HERTSMI-2 is a non-EPA scoring system derived from ERMI results that focuses on five specific water-damage molds. Some clinicians and consultants use it as part of their evaluation protocols for patients with suspected mold-related health issues, but it is not an EPA standard and is not universally accepted in the industry. Like ERMI, it should not be used as the sole basis for major remediation decisions.

  • Focuses on 5 specific water-damage molds
  • Used by some practitioners for health assessments
  • Not an EPA-endorsed standard
  • Should supplement, not replace, visual inspection

Important Limitations

EPA notes that ERMI was developed for research purposes and does not recommend using it to decide whether a specific home needs remediation. Dust samples vary based on where and how they are collected. Scores can change with cleaning, seasonal conditions, and occupant behavior. Like all mold testing, there are no federal exposure limits, so results require careful interpretation. Be wary of anyone using ERMI scores to push unnecessary services.

When Dust Testing Can Help

Dust testing can be useful for documenting conditions over time, comparing pre- and post-remediation dust levels, or gathering more detail when symptoms persist and other testing is inconclusive. Use it as a supplement to inspection, not a replacement. If you are experiencing ongoing health concerns, consider consulting a doctor alongside any environmental testing.

  • Documenting baseline conditions before purchase
  • Comparing pre- and post-remediation results
  • Investigating persistent symptoms with unclear source
  • Building a timeline of environmental conditions

Sample Collection Checklist

If you are collecting dust samples for ERMI or similar testing, follow these steps for accurate results:

  • Do not vacuum the collection area for 2-4 weeks before sampling
  • Use the lab-provided collection materials (usually a Swiffer cloth or vacuum cassette)
  • Collect from a consistent area (e.g., a specific room or square footage)

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5 more collection steps

Official Resources