ERMI and HERTSMI-2 Testing Explained: What a Home Mold Dust Test Can and Can’t Tell You

If you’ve spent any time in mold-illness groups, you’ve probably seen someone post an ERMI score and ask, “Is this bad?” The question makes sense. When you feel sick and suspect your home, a number feels like solid ground.

The honest answer is that a dust test can be useful, but it can’t tell you as much as many people hope. This post explains what these tests measure, how the scores are read in the CIRS world, what the agency that invented ERMI says about it, and how to use testing without being misled. For the medical side, see our Mold Toxicity and CIRS pages.

What ERMI actually measures

ERMI stands for Environmental Relative Moldiness Index. EPA researchers developed it using a DNA method that identifies and counts specific molds (mold-specific quantitative PCR) ^[1].

To build the scale, they analyzed 36 “indicator” molds in dust from more than 1,000 homes across the continental U.S., as part of a national housing survey, and ranked the homes from least to most moldy ^[1]. The resulting scale runs from about -10 to about 30. A home’s score estimates how moldy it is relative to that national sample ^[1].

In research, higher ERMI values have been linked with asthma. In one study, children whose homes had a high ERMI in infancy had more than twice the risk of asthma at age 7 ^{[1, 6]}. That’s real evidence, but it’s about risk across groups of people, not about whether one building is safe for one person.

What HERTSMI-2 measures

HERTSMI-2 was developed by Dr. Ritchie Shoemaker for patients with CIRS. It uses the same DNA testing but scores only five molds chosen from ERMI’s “Group I” list, using a point system ^[2]. Surviving Mold publishes this interpretation ^[2]:

• Under 11: “statistically safe for re-entry for those with CIRS”
• 11 to 15: “borderline; clean first and re-test before re-entry”
• Over 15: “dangerous for those with CIRS. Do not enter.”

The same page adds that HERTSMI-2 “is a building index,” that no single test “can possibly show all areas of a given building,” and that it “does not replace careful observation of symptoms” ^[2].

How CIRS practitioners use the scores

In the Shoemaker Protocol, removing exposure is the first and, as one summary puts it, the most critical yet most difficult step. Building testing with ERMI or HERTSMI-2 is part of that step ^[4].

Practitioners don’t all use the same ERMI target. One Shoemaker-trained physician’s summary uses an ERMI of 2 as the usual safety cut-off, and a stricter target for patients with certain lab results ^[4]. A data paper by Dr. Shoemaker and a colleague also uses 2 as the main cut-off ^[5]. If you’re working with a CIRS practitioner, ask which target they use for you and why.

What EPA says, and why it matters

EPA’s position is clear. Its fact sheet says ERMI “has been peer reviewed for research purposes but has not been validated for non-research purposes,” and “for this reason, EPA does not recommend the routine public use of ERMI in homes, schools, or other buildings” ^[1]. It adds that “inspection for water damage and mold remain the key to current EPA mold-assessment guidance” ^[1].

In 2013, EPA’s Office of Inspector General warned that the public may be making cleanup decisions based on a tool built for research, and that results could be overstated to persuade people into more costly remediation ^[7].

Other limitations have been reported too:

• A Finnish study (with one of ERMI’s developers as co-author) found ERMI was linked with some observations of visible mold but not with moisture damage, and concluded it isn’t equally usable in different climates and regions ^[8].
• Dr. Shoemaker’s own data paper acknowledges that ERMI “has been criticized as having methodological and mycological problems,” which is part of why he promotes HERTSMI-2 ^[5].
• More broadly, the CDC doesn’t recommend routine mold sampling. There are no set standards for an acceptable amount of mold, and visible mold should be removed whatever the type ^[9]. EPA notes there are no federal limits for mold ^[10].

So is it worth testing?

It depends on what you want the result to do.

A dust test may help if:

• You’re working with a CIRS practitioner who uses these scores to guide treatment decisions ^[4].
• You’re comparing places before a move, and you understand the result is one data point.
• You’ve remediated and want another data point alongside a visual check. CIRS practitioners often suggest testing again after remediation (Surviving Mold’s HERTSMI-2 guidance says to “clean first and re-test” borderline buildings), while EPA’s own completion checks focus on moisture being fixed, no visible mold or moldy odors, and people being able to re-occupy without health complaints ^{[2, 11]}.

A dust test is less useful if:

• You can already see mold or smell it. EPA says sampling is usually unnecessary when mold is visible; the job is to fix the moisture and remove it ^{[10, 11]}.
• You’re hoping it will prove or disprove that mold made you sick. It can’t do that ^{[1, 9]}.

Practical tips if you do test

• Fix and find first. Look for leaks, condensation, musty smells and past water damage, including hidden spots behind drywall, under carpet and above ceiling tiles ^[11].
• Follow the lab’s collection instructions exactly, and note which rooms and surfaces you sampled and when.
• Remember what one sample can’t show. A low score from one dust sample doesn’t clear every room, and HERTSMI-2’s own disclaimer says as much ^[2].
• Be wary of anyone who uses one score to sell expensive work. That’s the exact risk EPA’s Inspector General flagged ^[7]. Get a written plan that explains the moisture source and what will be removed.
• Watch how you feel. Surviving Mold itself says test scores don’t replace observing your symptoms ^[2].

What’s known and what’s debated

Generally accepted: finding and fixing moisture is the foundation of mold control; inspection for water damage is central to assessment ^{[1, 11]}.

Debated: whether ERMI or HERTSMI-2 scores can tell you whether a building is safe for a particular person. CIRS practitioners rely on them ^{[2, 4]}; EPA says ERMI isn’t validated for that use ^{[1, 3]}, and the HERTSMI-2 cut-offs rest on one clinician’s patient data, without independent validation that we could find ^[5].

Questions to ask

Your doctor or practitioner:

• What will we do differently depending on the result?
• Which score do you use as a target for me, and where does that number come from?
• Should I stay out of the building, or limit my time there, while we figure this out?

An inspector or remediator:

• Where is the moisture coming from, and how will it be fixed?
• What will you inspect beyond collecting a dust sample?
• How will we know the job is done, apart from a test score?

The bottom line

ERMI and HERTSMI-2 can be useful tools, especially if you’re working with a CIRS practitioner who uses them. Just don’t let a single number do more work than it can. Start with the moisture, inspect carefully, test with a clear purpose, and keep listening to your body. When you’re ready to act, our safe remediation guide and remediation decision tree walk through the next steps.

Sources

Numbers in brackets in the text link to these sources. Links were checked in October 2026. Some sources are written by people who support a particular approach; we've tried to say so in the text.

1. U.S. EPA. The Environmental Relative Moldiness Index (ERMI) fact sheet. September 2021. https://www.epa.gov/system/files/documents/2021-09/updated-fact-sheet.ermi-_9.9.21.final_new-template_508-compliant_0.pdf
2. Surviving Mold (Shoemaker RC). HERTSMI-2 Scoring System (web page). Web page, accessed October 10, 2026. https://www.survivingmold.com/resources-for-patients/diagnosis/hertsmi-2
3. U.S. EPA. Environmental Relative Moldiness Index (ERMI) (web page). Web page, accessed October 10, 2026. https://www.epa.gov/air-research/environmental-relative-moldiness-index-ermi
4. Ou D. Steps of the Shoemaker Protocol (2014; hosted by Surviving Mold). https://www.survivingmold.com/STEPS_OF_THE_SHOEMAKER_PROTOCOL_3.PDF
5. Shoemaker RC, Lark D. HERTSMI-2 and ERMI: Correlating Human Health Risk with Mold Specific qPCR in Water-Damaged Buildings. Manuscript dated May 22, 2016, hosted by Surviving Mold (publication venue not confirmed). https://www.survivingmold.com/Publications/HERTSMI-2_AND_ERMI_5_22_2016__CORRELATING_HUMAN_HEALTH_RISK_WITH_MOLD_SPECIFIC_QPCR_IN_WATER_DAMAGED_BUILDINGS_CLEAN.pdf
6. Reponen T, Vesper S, Levin L, et al. High environmental relative moldiness index during infancy as a predictor of asthma at 7 years of age. Ann Allergy Asthma Immunol. 2011;107(2):120-126. PMID: 21802019. https://doi.org/10.1016/j.anai.2011.04.018
7. U.S. EPA Office of Inspector General. Public May Be Making Indoor Mold Cleanup Decisions Based on EPA Tool Developed Only for Research Applications. Report No. 13-P-0356, August 22, 2013. https://www.epa.gov/office-inspector-general/report-public-may-be-making-indoor-mold-cleanup-decisions-based-epa-tool
8. Täubel M, Karvonen AM, Reponen T, Hyvärinen A, Vesper S, Pekkanen J. Application of the Environmental Relative Moldiness Index in Finland. Appl Environ Microbiol. 2016;82(2):578-584. PMID: 26546428. https://doi.org/10.1128/AEM.02785-15
9. Centers for Disease Control and Prevention (CDC), National Center for Environmental Health. Mold (About mold). Reviewed Sept 26, 2024. https://www.cdc.gov/mold-health/about/index.html
10. U.S. EPA. Mold Testing or Sampling. Web page, accessed October 10, 2026. https://www.epa.gov/mold/mold-testing-or-sampling
11. U.S. Environmental Protection Agency (EPA). A Brief Guide to Mold, Moisture and Your Home. Web page, accessed October 10, 2026. https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home
12. MedlinePlus. Asthma. Web page, accessed October 10, 2026. https://medlineplus.gov/ency/article/000141.htm
13. MedlinePlus (U.S. National Library of Medicine). Anaphylaxis. Web page, accessed October 10, 2026. https://medlineplus.gov/ency/article/000844.htm