How to Interpret Your ERMI and HERTSMI-2 Scores: A Step-by-Step Guide

HERTSMI-2 scores below 11 indicate your home is likely safe for sensitive individuals. Scores between 11 and 15 are borderline, meaning caution and remediation are advised. Scores above 15 are dangerous and signal an unsafe environment. ERMI scores range from roughly -10 to +30, with higher values indicating more water-damage mold relative to your home's background levels. You can calculate your HERTSMI-2 directly from an ERMI report because it uses 5 of the same 36 species. Source: Shoemaker & Lark

Key takeaways:

• HERTSMI-2 below 11 = likely safe (98% likelihood). Between 11-15 = borderline. Above 15 = dangerous.
• Both tests use DNA analysis of dust samples, not air sampling or visual inspection.
• Scores are a starting point for decisions, not the sole basis for major life changes.

One thing to remember: A number on a report doesn't tell the whole story. Pair your score with professional interpretation and your own symptom history before making major decisions.

Need to test your home? Order a HERTSMI-2 Home Test Kit ($199, all 50 states).

Overview: Why Your Mold Score Matters

You got your lab report back. There's a number on it. And you have no idea what it means.

You're not alone. As one person navigating mold illness put it: "I find the sheer amount of information overwhelming and impossible for me to process. I need very simple, clear instructions and short writings." (r/ToxicMoldExposure)

This guide gives you that: no jargon walls, no 40-page PDFs. Just a clear walkthrough of what your score means, what each threshold tells you, and what to do next.

ERMI and HERTSMI-2 are DNA-based dust tests. Unlike a hardware-store kit that simply says "mold present," they identify and quantify specific water-damage mold species in your home's dust. That species-level data is what makes them useful for health decisions.

If you don't have your test results yet, MoldCo's Mold Home Test Kit ($199, all 50 states) uses the HERTSMI-2 method and ships directly to your door.

If you're still figuring out whether mold could be behind your symptoms, start with our signs of mold exposure page.

Before You Start

Make sure you have these items in front of you:

1. Your ERMI or HERTSMI-2 lab report with species-level data (not just a single number).
2. A record of known water damage events in your home: leaks, floods, condensation problems.
3. Your symptom history timeline. When did symptoms start? Did they coincide with a move, renovation, or water event?

Already have an ERMI report? You can derive your HERTSMI-2 score directly from it. HERTSMI-2 uses 5 of the 36 species that ERMI already measures. Same dust sample, same lab analysis.

Don't have a test yet? See the home test kit in the Overview above or jump to Next Steps.

Step 1: Understand What Your Test Measures

These tests aren't like petri-dish kits from a hardware store. ERMI and HERTSMI-2 use MSQPCR (Mold Specific Quantitative Polymerase Chain Reaction) to identify and count specific mold species by their DNA. Instead of growing mold on a dish and guessing, the lab reads the DNA in your dust to tell you which species are present and how much of each.

What Is ERMI?

ERMI (Environmental Relative Moldiness Index) was developed by EPA researchers using MSQPCR analysis of dust samples from 1,096 nationally representative homes.

It measures 36 mold species: 26 "Group 1" species linked to water damage and 10 "Group 2" common background molds found in most homes. Your ERMI score is the difference between these two groups, on a scale from roughly -10 (very low moldiness) to +30 (very high).

Translation: ERMI tells you how moldy your home is compared to average U.S. homes, based on the DNA of 36 mold species in your dust.

What Is HERTSMI-2?

HERTSMI-2 was developed by Dr. Ritchie Shoemaker and Mycometrics Lab (Kin Teh Li) to focus on the 5 mold species most linked to water-damage illness. For a deeper look at the protocol behind this work, see the Shoemaker Protocol roadmap.

Those 5 species are:

• Aspergillus penicillioides
• Aspergillus versicolor
• Chaetomium globosum
• Stachybotrys chartarum
• Wallemia sebi

HERTSMI-2 applies a weighted scoring system to these species. The result is a single number that predicts whether your home is safe, borderline, or dangerous for people sensitive to water-damage molds.

An Important Note on ERMI's Status

The EPA considers ERMI a research tool and has stated it "has been peer reviewed for research purposes but has not been validated for non-research purposes." We won't pretend otherwise.

That said, ERMI has been studied in peer-reviewed literature across thousands of homes and is commercially licensed to labs. Used correctly, it's a quantitative way to measure species-specific mold burden in dust and track changes over time.

Step 2: Read Your HERTSMI-2 Score

Here are the three tiers, based on research by Shoemaker & Lark:

HERTSMI-2 Below 11: Likely Safe

Your home is generally considered safe for sensitive individuals, with approximately a 98% likelihood it's safe to remain.

What to do: If symptoms persist, the exposure may have occurred in a previous home or workplace. Consider a MoldCo care evaluation to address lingering health effects even after you've left the source.

HERTSMI-2 = 11-15: Borderline

Caution and remediation are advised. This range is not recommended for people with suspected mold illness (CIRS).

What to do: Get an independent indoor environmental professional (IEP) to assess your home. Start aggressive cleaning and consider air purification. MoldCo supports starting treatment even in borderline environments---don't delay care while you work to improve your space.

HERTSMI-2 Above 15: Dangerous

An unsafe environment for sensitive individuals. In this framework, 16+ is dangerous. A score of 20 is firmly in the dangerous range, not borderline.

What to do: Professional remediation (following IICRC S520 or higher standards) or relocation should be your priority. Make sure the person testing your home is independent from the person doing the remediation.

One person dealing with severe mold described the reality: "I sleep in the car in my driveway and I have been stripped of basic necessities including hygiene." (r/ToxicMoldExposure)

Scores in this range require action, not deliberation.

Species-Level Clues

Elevated Chaetomium globosum or Stachybotrys chartarum suggests near-standing water for weeks to months. These species don't grow from minor condensation. They need sustained, serious moisture.

The key finding from Shoemaker's research: "While high scores of both ERMI and HERTSMI-2 accurately predicted markedly increased risk of recrudescence, only low HERTSMI-2 predicted safety from re-exposure for patients who had prior CIRS-WDB."

Translation: A high ERMI can warn you of danger. Only a low HERTSMI-2 can tell you a home is actually safe to live in.

Step 3: Interpret Your ERMI Score

ERMI works differently from HERTSMI-2. Instead of a weighted health-risk score, it calculates the difference between water-damage molds and common background molds.

Here's how the math works: the lab sums the log-transformed concentrations of 26 Group 1 molds (water-damage species), then subtracts the sum of 10 Group 2 molds (common indoor species).

• Group 1 molds: 26 species associated with water damage. More of these = higher score.
• Group 2 molds: 10 common indoor molds not linked to water damage. These are subtracted.

What the Numbers Mean in Practice

• Asthmatic children in Boston, Kansas City, and San Diego lived in homes with an average ERMI of 8.73. Healthy controls averaged 3.87.
• Children in high-ERMI homes (>= 5.2) at age 1 had 2.6 times the risk of developing asthma (adjusted odds ratio 2.6; 95% CI 1.10-6.26).
• In Shoemaker's research, ERMI >= 2.01 predicted re-acquisition of abnormal inflammatory markers after re-exposure. But ERMI alone could not predict the absence of relapse.

That last point is why HERTSMI-2 was developed. ERMI can flag danger, but the total ERMI score alone can also be deceptive without interpretation.

ERMI contains multiple layers of useful information (Group 1 vs. Group 2, the full 36-species table, and any lab flags). HERTSMI-2 is essentially an abbreviated ERMI designed to make decision-making simpler for people who are already overwhelmed.

If you have an ERMI report, you can calculate your HERTSMI-2 from it. Same dust sample, same lab analysis. HERTSMI-2 uses 5 of the 36 ERMI species. Ask your lab to calculate it, or use an online calculator.

Step 4: Decide What to Do Next

A practical guardrail: Don't use ERMI or HERTSMI-2 scores as the sole basis for major life or financial decisions. Use them alongside building history, moisture evidence, symptoms, and professional interpretation.

Professional interpretation is much more valuable than the score alone. Using the thresholds from Step 2, here is a decision framework:

Score Below 11: Your Home Is Likely Safe

If symptoms persist, previous exposure or another location (workplace, school, car) may be the source.

Your next step: A clinical evaluation to address ongoing symptoms from prior exposure. Our CIRS treatment guide explains the treatment path.

Score 11-15: Your Environment Needs Improvement

This may not require a full move, but it does require action.

Your next steps:

• Hire an independent IEP for a thorough assessment.
• Start aggressive cleaning and air purification.
• If you clean belongings, don't bring them back into an unremediated space. Move them directly to a clean space or sealed storage.
• Don't wait for a perfect environment to begin treatment. Finding a fully clean space can take months or years.

Score Above 15: Strong Evidence of Toxic Exposure

Your next steps:

• Professional remediation (IICRC S520 or higher) or relocation.
• Hire an independent tester---not the person doing the remediation.
• Begin treatment alongside environmental changes.

Need help interpreting your results? Start with a MoldCo care evaluation. Our providers are trained in the Shoemaker Protocol and can turn a confusing score into a clear path forward.

Step 5: Verify After Remediation

Remediation isn't done until the numbers say it's done.

After remediation and cleaning are complete, wait approximately 4 weeks for new dust to accumulate. Then retest using HERTSMI-2 dust testing. Your target: below 11.

Why Dust Testing Beats Spore Traps

Many remediators offer a "spore trap clearance test" as proof of successful work. Be cautious. A negative clearance test doesn't mean the remediation was done correctly. Spore traps capture only what's airborne at a single moment. Dust tests capture accumulated fungal DNA since the last deep cleaning (often weeks, but sometimes months or years), giving a much more reliable picture.

Hire Independent Testers

Your post-remediation tester should be someone other than the remediation company. Conflicts of interest are real.

What If Symptoms Return After Moving?

One reader shared: "We recently moved out of a moldy environment. I felt amazing for 3-4 days... Since then I have been incredibly reactive." Another asked: "Are we all shedding the mold and mycotoxins as we're out and contaminating this house?" (r/ToxicMoldExposure)

Cross-contamination is real. If symptoms return after moving, don't assume the new building is the problem. First, consider what you brought with you (clothing, furniture, luggage) and whether items were cleaned and stored in a clean zone. Then test the new space with HERTSMI-2. Data replaces fear.

Common Mistakes When Interpreting Mold Test Scores

For post-remediation verification mistakes, see Step 5.

1. Using the score as your only decision-maker

Professional interpretation of the raw data is often more valuable than the score alone. Scores work best alongside professional assessment, visual inspection, and moisture testing.

2. Trusting DIY mold tests from hardware stores

One person shared: "I ordered a DIY test for mold from Amazon, and it was positive." (r/ToxicMoldExposure) A positive settle-plate result tells you mold exists (it does everywhere). It doesn't tell you which species or how much---the difference between a "yes/no" and actionable health data.

3. Confusing environmental tests with clinical testing

ERMI and HERTSMI-2 test your environment (dust DNA). Clinical evaluation and lab work help assess your body's response. These answer different questions.

4. Using the wrong dust collection method

Small differences in dust collection can change results. Follow your lab's instructions exactly and use the same collection method each time you retest (so changes reflect the building, not your sampling method).

5. Starting treatment without testing your environment

Taking binders without knowing your environment is like bailing water without plugging the hole. Test first. Then treat.

FAQ

Can I calculate HERTSMI-2 from my ERMI results?

Yes. ERMI reports are built from species-level MSQPCR results for 36 molds. HERTSMI-2 uses 5 of those same species, so you can derive your HERTSMI-2 score from your ERMI data (same dust sample, same lab analysis).

How accurate is the ERMI test?

The EPA notes ERMI has not been validated through a multi-lab study.

In real-world use, ERMI is best treated as an index for comparing environments and tracking change (especially pre/post remediation). The more consistent your sampling method, the more useful your results.

How often should I retest?

After remediation (wait about 4 weeks for dust to accumulate), if symptoms change significantly, and before moving into a new home if you have a history of mold sensitivity.

My score is borderline (11-15). Should I move?

Not necessarily. A borderline score warrants investigation and remediation, not immediate relocation. Get a professional IEP assessment. Consider your symptoms, exposure duration, and whether remediation is feasible. MoldCo supports starting treatment even in borderline environments.

What's the difference between ERMI and air sampling?

Dust tests like ERMI and HERTSMI-2 capture accumulated fungal DNA over time since the last deep cleaning (often weeks, but sometimes months or years). Air sampling captures only what's airborne at one moment. A quiet day could produce a "clean" air sample even in a heavily contaminated home. For health investigations, dust-based DNA testing is more reliable.

Next Steps

You have your score. Now you need a plan.

1. Need to test your home? Order the MoldCo Mold Home Test Kit ($199). HERTSMI-2 method, ships to your door, all 50 states. Results in 1-2 weeks.

2. Have your score and need help making sense of it? Start a MoldCo care evaluation. Our providers are trained in Dr. Shoemaker's Protocol and can build a clear treatment plan guided by your environmental and health data.

3. Want to understand what's happening in your body? The Starter Health Panel ($99) measures 3 key biomarkers through LabCorp that reveal how mold exposure may be affecting your inflammation, hormones, and immune system.

The worst thing you can do with a mold problem is wait.

Any health-related claims made on this site have not been evaluated by the Food and Drug Administration (FDA). The information provided on this site is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. MoldCo assumes no responsibility or liability for any errors or omissions in the content of the references, nor for any actions taken in reliance thereon.