ERMI vs HERTSMI-2: Which Mold Test for Your Building?

Why the typical "mold inspection" misses the problem

When you call a standard mold inspector, you typically get an air sample. Air sampling catches actively releasing spores at the moment of the test. It misses:

• Dormant water damage (most chronic exposures)
• Mold inside walls, under floors, in HVAC
• Hyphal fragments and mycotoxins that don't aerosolise
• Cumulative exposure history

That's why patients with raging CIRS get "your house is fine" reports.

What ERMI and HERTSMI-2 actually measure

Both are dust-based quantitative PCR tests that detect DNA of specific mold species. Because dust accumulates over months-to-years, these tests give a much better picture of total exposure history than air sampling.

ERMI (Environmental Relative Moldiness Index)

• Measures 36 mold species — 26 "Group 1" (water-damage-associated) and 10 "Group 2" (common indoor mold)
• Calculates a single index score: Group 1 minus Group 2
• Best for: initial investigation, understanding the full mold ecology, real-estate decisions
• Cost: ~$290

HERTSMI-2 (Health Effects Roster of Type-Specific Formers of Mycotoxins and Inflammagens)

• Measures 5 species Dr. Shoemaker identified as most strongly linked to CIRS: Aspergillus penicillioides, A. versicolor, Chaetomium globosum, Stachybotrys chartarum, Wallemia sebi
• Generates a 0–15 score
• Best for: re-test after remediation, deciding whether a building is safe to re-occupy
• Cost: ~$160

How to choose

• First test: ERMI. Better picture of the full landscape.
• Post-remediation re-test: HERTSMI-2. Cheaper, faster, focused on the species that matter for health.
• Multiple buildings to triage (e.g., picking a new rental): HERTSMI-2 across all candidates.

How to collect

Both use a Swiffer cloth wiped across surfaces in a specific pattern — typically 2 sq metres of horizontal surfaces in 2–3 rooms, including HVAC vents. Follow the lab's instructions exactly; sampling technique drives accuracy more than test choice.

How to interpret

ERMI: Above 2 is moderately concerning, above 5 is high. Negative scores (more Group 2 than Group 1) are typically safe.

HERTSMI-2:

• 0–10: low-risk for re-entry by CIRS patient
• 11–15: do not re-occupy without further remediation

These thresholds are conservative for CIRS-susceptible patients. Healthy people tolerate higher loads.

Where the building work fits

Testing the building is layer 1 of the mold treatment sequence. Patient detox without environmental work fails.

Read next

• Mold illness symptoms checklist
• Mycotoxin binders comparison guide
• Mold + mast cell activation link
• Mold illness pillar