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ERMI Testing Vs. Air Samples

ERMI test; ERMI logo

Very often we receive calls from very concerned people that need help determining if they need an Environmental Relative Moldiness Index (ERMI) test or not.  The range of knowledge in the general public for this type of test varies.  In this post, I will highlight a few points to keep in mind when deciding on doing an ERMI test. First, let me provide some information per the Environmental Protection Agency’s (EPA) website on ERMI testing.  ERMI stands for Environmental Relative Moldiness Index.  The analysis from this test can be used by researchers to estimate the levels and types of mold inside a property.  The test is done by collecting a dust sample.  Since mold spores can settle onto dust, the DNA from the mold in the dust can be identified, thereby providing information on what types of mold are present.  However (and this is highlighted in bold lettering on the EPA website), “the ERMI should be used only for research.  The ERMI has not been validated for routine public use in homes, schools, or other buildings.”  The EPA also recommends that water damage is assessed during the inspection since moisture issues are what cause most mold problems.  

Our company performs several types of mold tests including ERMI and air samples.   Air samples differ from ERMI because no settled dust is used.  Instead, air is drawn through a cassette and any spores present are deposited onto a glass slide in the cassette and ultimately viewed through a microscope.  The laboratory analysis can tell us the concentration of mold that was found in the air along with the types of mold (generally, down to the genus level).  

So the main difference is that ERMI collects spores and DNA from dust, whereas air samples collect spores from the air.  What’s the big difference?  The spores settled in the dust provide more historical information and air samples provide more current information.  Is one better?  Not really, they are just different.  Analysis between the two types is another main difference with ERMI detecting DNA via polymerase chain reaction and most air samples being analyzed via the microscope.

ERMI tests use a statistical formula to provide a single ERMI number.  Interpreting that ERMI number can be a big challenge.

When potential clients ask us to perform an ERMI test, we first recommend that we do a visual inspection and moisture evaluation.  We recommend that they also do more traditional spore trap testing alongside ERMI.  This way we can provide them with both historical and current information regarding the mold levels in their home.   

This blog article is just scratching the surface about ERMI.  Please leave a comment if you have any questions.

Click on this link to find the EPA Website.

Ian Cull

Ian Cull is a nationally recognized expert in the field of indoor air quality. He is the Chief Science Officer of Indoor Science, a company he started in 2004. He speaks around the world on air quality topics and is a training provider of the Indoor Air Quality Association. Mr. Cull is a Licensed Professional Engineer (PE) and Certified Industrial Hygienist (CIH). His degree is in Environmental Engineering from the University of Illinois - Urbana Champaign. Mr. Cull has developed 50 air quality related courses for the IAQA University and is the author of the book, “Fundamentals of Mold Remediation”. In his words… “Besides being passionate about indoor air quality, I enjoy cycling, music, the Chicago Bulls, and having fun with my three kids.”

52 thoughts on “ERMI Testing Vs. Air Samples

    I did an ermi test inside are building and it came back with high levels of mold my employer will not do a thing about it

    Hi Joel
    I am hoping that you can guide me. I am a real estate broker in Southern California. I am representing both the buyer and the seller in this transaction. The buyer has a history of health issues related to mold. The house he is purchasing is meticulous. It was so clean that he had to search multiple areas in order to gather samples. The dust he collected was on areas of furniture that probably had not been touched in many years. His ERMI test came back high. We then hired a mold inspector to test the air quality in multiple rooms. The results came back with very low to absolutely no evidence of mold. Is there somebody that we can hire to make sense of the two reports for us? Are there any other inspections or professionals that can provide information to all of us? We are all at a loss and not sure how to proceed. Any direction or information would be greatly appreciated. This buyer loves this home and doesn’t want to walk away from his dream home, but he is also in fear of past health issues returning. Please help……
    Thank you!


    “Should I test or sample for mold in my home using the Environmental Relative Moldiness Index, or ERMI?
    No. The Environmental Relative Moldiness Index, or ERMI, developed by U.S. Environmental Protection Agency researchers, is a research tool and is not recommended for use except as a research tool.” https://www.epa.gov/indoor-air-quality-iaq/should-i-test-or-sample-mold-my-home-using-environmental-relative-moldiness-0

    The quotation above is directly from the EPA. A dust sample is collected and analyzed when using ERMI. To compare the numerical results directly with the index developed for ERMI, the dust sample would have to mirror the samples collected in the index. In the research study that developed the ERMI test the sample was collected from the living area and bedroom areas of a home. If you deviate from those areas to collect the sample then it makes it difficult to compare the score you receive from the ERMI index.

    Hi Joel, thanks for sharing.

    A few more words about ERMI. DNA mold analysis is 99.99% accurate. Out of all the other mold testing methods, the best is 56% accurate. No other test will provide data nearly as reliable as MSQPCR, which ERMI uses.


    Hi Joe,
    My daughter is a CIRS patient and is having to move from her current condo to another one because of known water damage that was repaired, but we don’t believe the mold was remediated correctly. My question is, what testing would be best for her new place prior to move in (we don’t see any visible signs of water damage or mold) , and what is she to do with furniture, rugs, and her belongings that have been in the old place? How do we completely clean things so she can have a fresh start? Thank you for your help.

    Having a professional inspect the new property would be ideal. They should look for active moisture with equipment such as an infrared camera and a moisture meter. But most importantly the company you hire should NOT offer any remediation services or sell products or else there is a conflict of interest.

    I would recommend following the IICRC recommendations on personal items that were in the old property. Typically, if there is no visible mold on a material they could be laundered, dry cleaned, and/or HEPA vacuumed. If you hire a company to clean these products ensure that they follow IICRC guidelines.

    Thank you for commenting.

    We moved into new construction housed 10 months ago. Chronic sinus ache the last 7 months. The amount of dust is high and looks different. We live in northern Michigan and the house has been closed up for the 7 months. I would like to get my dust tested. Do you feel this will lead to solving my problem?


    You can always perform IAQ testing to get a better understanding of the overall picture of your home’s air quality. However, I will advise that dividing and conquering may be helpful. Note times of the day that your symptoms worsen, are you in one room of the home? are there any musty odors? have you completed any renovations? do you feel better seasonally or is it year-round? etc. Unfortunately, there is not 1 sample that can be collected and be analyzed for every imaginable contaminant that may be in that sample. Typically, we have to know what we are looking for to see if it’s present in a sample.

    Thank you for commenting.

    Have you seen instances of ERMI tests showing a problem, but there not being one upon thorough inspection? We did a HERTSMI and the score is 18. Should be under 15, preferably 11. It is mainly because of aspergillus penicillioides which came back at 670 Spore E./mg. Do you consider that a high amount of that type of mold? Thank you.

    Yes, we have seen instances where an inspection does not show signs of moisture or mold but ERMI scores indicate that there is a problem. You have to remember that the ERMI sample is a dust sample. If you think of dust in your home, the length of time the dust has been collecting can vary. The dustier and longer dust has been collecting the higher the likelihood the ERMI score will be high. Sometimes it may be worth putting more stock in a thorough inspection versus a score. It is difficult to say if a specific number of a specific type of mold is elevated, I would consider the overall picture of your property (history of water damage, recent renovations, humidity levels, is there visible mold?, has there been mold remediation completed? etc).

    The ERMI test is US governent approved. I did an ERMI test after being sick for a long time it came back back with results showing that the building I work in has a mold problem. What happens is we have an employee that is over the buildings and he reads the above blog and brings it to the attention of management stating the ERMI test I did is not valid. I also did a urine and the environmental company said based on your mycotoxin test (urine) and the ERMI test it clearly shows your lab and the ERMI test is showing q direct correlation between them
    Are you starting it is all BS.


    im very concerned about my prior workplace being very unsafe. I tested positive for multiple toxic molds. my dr had my previous employer test. the first set of tests showed low levels of aspergillus spores and moderate levels of stachybotrys spores in the basement where some of my co-workers had heard that the basement was covered in mold which is below our work space. the building has always smelled of mold and heating is circulated from the basement and there is no windows that can be opened on main floor where i worked.
    the company testing the mold said there was no way that the spores found in the basement could come up to the main floor. my dr disagreed and said they needed to do a mycotoxin test. they did one through realtime labs and it came back negative. i have learned that stachybotrys is a mold that always produces mycotoxins which means its still in the bldg. realtime did dust samples and im very interested in what you’re saying about the ERMI testing versus the EMMA testing that realtime does. also, when the employer found the mold in basement they removed all furniture from basement, fixed a leak and treated the filtration system-could this be why the second test was negative. should the employer be doing further testing? this is a clinic for individuals being treated medically, for mental health and substance use disorders so there’s dr’s, patients, clients, staff and people in and out of bldg and people with severe and persistent mental illness living in the above apartments. im in oregon and have called OSHA, but they can only do minimal. any thoughts/feedback?


    EMMA uses similar analysis methods as ERMI. One of the main differences is that EMMA includes mycotoxin testing. Unfortunately, there are too many variables here that I cannot comment on. I would recommend following your doctor’s advice. Thank you for commenting.

    It sounds like they did some work to clean up the space. If they did it properly it is possible that any testing after the remediation would show lowers levels of mold.

    Also, it depends on how the building is structured but usually if there is mold in the basement and especially a substantial amount of mold, it is possible for mold to seep up to the level above due to Stack Effect.

    Thank You!

    I am a CIE but have little knowledge on remediation.
    Can you suggest the best course to take, through indoor science of otherwise, to get a cert in that so that I can write more educated protocols for my clients?

    Since Air-o-cell analysis is different than DNA or ERMI, would you perform a test with one for pretesting and the other to define how well the property has been cleaned after remediation. (Using the ERMI method for Post Cleanup)?

    A lot of times the testing ends up being what the client prefers, but consistency would be ideal so you are comparing results from the same type of test.

    We had our house remediated twice due to toxic mold. We also did major repairs to fix the problems that caused the mold. We are planning on selling the house should we get ermi testing of air samples?


    Prior the selling the home you may want to consider having a mold professional at least do a visual inspection and check for moisture in the home. It’s up to you as to which method you prefer in terms of testing, keep in mind that air samples tell you what is in the air at the time of the sampling and an ERMI test is a dust sample that will give you more of a historical perspective what molds have been in the home.

    Best of luck!

    Is it true when you do the ERMI test that you have to wait for 4 weeks of dust accumulating before you actuallu take the sample for testing?

    Have you read the “Is ERMI Testing Being Used For Its Intended Purpose?
    by Gary Rosen, Ph.D.

    And thoughts on his paper?

    We had a serious mold problem on our top two floors. We went through remediation; replaced duct work as well as HVAC system. A few weeks ago I went to a Dr who said I had biotoxin issues. I was told to have an ERMI test which came back positive for air borne mold. There are no signs of mildew or moisture in the house that we can see. I’ve now been told to clean the house with a vodka and water solution from floor to ceiling and have another ERMI test completed. I also have the HVAC Co suggesting I put an air purifier in the duct work. Any guidance you can provide would be greatly appreciated.

    Thank you for the information. Our ERMI dust cloth test score came back high (13.42), but our air samples came back very low. We found no sources of mold. Do you have a possible explanation for the high ERMI score?


    Air sampling is a good tool to use when you want to know current mold conditions in your home. It provides you with results that show you the mold counts in the air in a snapshot in time (when the samples were collected). ERMI, on the other hand, is a dust sample that is analyzed. Mold is always naturally floating around the air but at some point, it settles. Over time the mold spores may accumulate in that dust and yield a higher ERMI score. This is why we generally like to look at the ERMI test as a historical perspective of the types of mold that have been in your home whereas we look at the air samples of what is going on right now.

    Thank you for commenting!

    Air samplers have lots of problems and short comings when sampling form mold

    We had a buyer do a ERMI test in our house. Buyer bought a test online and was given swipe rags (up to 10 rooms) and stuck them in a plastic bag and sent to a lab. The rags weren’t labeled as to where they were taken. I watched her swipe inside cabinets and saw swipe marks on window ledges that haven’t been cleaned in 10 years. Cross contamination? Maybe. We don’t have water damage. No smell. No mold issues (we actually had a mold inspector come and inspect). No respiratory issues. Ever. But my husband is a gardener, we have 2 dogs and we’ve done construction. And I’m not the greatest cleaning person. Some of the levels came back high. There was no outside base count. We live in an area that has a lot of rain. It upsets me that the comparison is an average of 1100 homes across the country without any consideration for regional difference or current outside conditions. This test makes people crazy and should not not encouraged. They aren’t FDA approved or conducted by licensed professionals.

    am I able to get your input and opinion on both an ERMI sample as well as an air quality sample?

    Hi Joel,
    I’m curious if you have compiled a list of reputable mold inspectors throughout the U.S.? Unfortunately, we are not in Chicago (we are in centeral Ohio) and it seems extremely difficult to find not only qualified mold inspectors but qualified companies to then remediate any problems. F

    So we found mold in the attic. At some point prior to our moving in 8 years ago, the homeowners added extra insulation into the attic which blocked proper airflow around the soffits. My husband plans to go into the attic and kill the mold with a specific type of spray (can’t remember name, sorry), push the sprayed insulation away from soffits and paint killz on the ply-boards which will allow us to easily see if the mold comes back. My initial question is, having not seen mold in the house, almost never going up into the attic, and with a layer of insulation between the attic and our upstairs ceilings, have we been affected by the mold over the years or is it contained upstairs? Can mold effect you if it’s behind a wall and not visible? Are the ERMI and air tests the only way to know if it’s in your house? Thx for any thoughts/insight!!

    Generally, air moves from the bottom of your home to the top where the attic is located, so the air from the attic is likely moving up and out but it is possible for some attic air to penetrate down.

    It is possible for spores from behind the wall or ceiling to move through openings such as from can light fixtures out light switch covers.

    The best way to determine if there is mold is with a visual inspection. Mold air samples and ERMI testing are useful tools to use when there is hidden mold.

    Hello, if a person is suffering from mold toxicity, would an ERMI test be more definitive in measuring the mold – would the standards be different for someone who is suffering from mold toxicity? Seems like ERMI is suggested for lyme / mold patients. We are facing that and I don’t know how to remediate to the degree I suspect an ERMI test would indicate.

    A group of doctors at the forefront of studying mold toxicity prefers ERMI testing. So if you are under the care of one of these physicians, they will typically be instructing you to do an ERMI test.

    There are a number of peer-reviewed articles published in journals finding an association between asthma and ERMI score. However, I’m not aware of journal articles showing the ERMI score being associated with mold toxicity. I’m guessing this is either because of a lack of consensus on defining mold toxicity, or just that I haven’t come across those articles.

    I think it is acceptable to do ERMI testing, so long as it is done in conjunction with a thorough mold and moisture inspection.

    Hi. In response to the above comment that Penicillium/Aspergillus are not considered toxigenic, are you referring to a specific sub species? Because it is well documented that Aspergillus niger produces the toxins “malformin C” and “ochratoxin A,” and is a known causal agent of the type of ear infection called “Otomycosis.” There is also a medical diagnosis called IPA (invasive pulmonary Aspergillosis) which is essentially a fungal ball growth of aspergillus in the lungs that immune compromised and people with COPD (for example) can develop from inhaling elevated levels of aspergillus spores. There is also a mycotoxin called “aflatoxin” produced by Aspergillus flavus that is considered a serious carcinogen. You may want to revise/clarify your statement for purposes of liability as an IAQ professional.


    Thank you for pointing that out. You are correct, there are subspecies that are considered toxigenic. I edited the post.


    I emailed him directly with a response but I will post below what I sent him in case it is helpful for you or other people.

    Thank you for commenting Jen!


    An ERMI result is difficult to interpret that is why the EPA currently uses it as a research tool and not as a means to determine if there is a mold problem in a home. Whenever a client requests an ERMI test we also recommend getting air sampling done through a spore trap in order to get a better picture.

    Every situation is unique inside a home and the amount of mold in it can vary depending on the situation. Without doing an inspection and our own sampling it is difficult to tell you definitively what the mold issues in your home are. With that said, I can tell you that an air sample result of 350 spores/m3 of Aspergillus/Penicillium is not usually considered elevated. It is true that the outdoor control sample is the comparison that is used to determine if a particular mold level inside the home is high. However, in the midwest, for example, it is common for outdoor Aspergillus/Penicillium mold to be above 1,000 spores/m3 during the warmer months.

    Also, remember that mold is EVERYWHERE and it would be a nearly impossible task to 100% eliminate it from the air.

    If you still have concerns and you’re in the Chicagoland area consider having us do a mold inspection of your home.


    *Edited: 1.29.2018*

    Even though this is an old post, I think it’s important to follow up on the interpretation of the ERMI, for the ERMI is more reliable than an air sample — and it’s not so difficult. [Of course, do correct anything I get wrong. With citations please].

    First, it’s quite true that one strength (and weakness) of an ERMI sample is that it’s not just a snapshot, but an average of the contamination in that room or rooms over time. More importantly, unlike the air samples which cannot differentiate even between Aspergillus/Penicilium molds, the ERMI uses DNA testing. Thus it report differentiates between “benign” outdoor species and ones rarely in indoor air unless there’s been water damage. Third, an ERMI counts DNA, whether from spores or tiny mold fragments, and as there can be thousands more fragments than spores, and the fragments are what goes deep into the lungs, that seems to have better face validity. Lastly, while it’s true that the EPA warn against using ERMI to screen homes, their own research shows that ERMI measurements (of Group 1 molds, see below) correlates well with 48-hour air samples (Cox et al, 2017, “Comparison of indoor air sampling and dust collection methods for fungal exposure assessment using quantitative PCR” Environ Sci Process Impacts. 2017 Oct 18; 19(10): 1312–1319).

    So what about an ERMI of 22?

    First, to get an ERMI of 22, the dust must include some specific indoor water-damage (Group 1) species at WAY higher concentration than the air sample showed. Especially for heavy, sticky spores (like Stachy or Chaetomium), air sampling of a quiet room may not show them — but ERMI sampling of dust will. And life activities, like toddlers and dogs running around, opening/closing windows and doors, vacuuming, will all send them into the air… and then they redeposit through the house. An ERMI of 22 does indicate major contamination of the house dust (from the old source, or other wall cavities or a crawl space).

    Why is the ERMI score important?

    An ERMI score is the difference between the concentration of water-damage molds (Group 1 molds) that may produce mold-poisons (mycotoxins) and benign outdoor-growing molds blown in (Group 2 molds). The ERMI formula uses logarithms, and a score of 22 means that some of those water-damage-indicator (Group 1) molds must have been thousands of times higher vs. the Group 2 molds.

    The problem is that most of these Group 1 species are good at germ warfare — their spores and hyphae fragments are covered in poisons (mycotoxins) and the fragments are tiny enough to get deep into the lungs — so for folks who are sensitive, these fragments are at least as dangerous dead as alive. Some mycotoxins only cause problems if inhaled, others (like from Stachy) are also absorbed through the skin, so imagine little kids playing on carpet, and anyone sleeping with a long-haired cat or dog….

    However, the total ERMI number is not enough. With a count of 22, a good mold hygienist would likely do another sample or few, and study the specific Group 1 and 2 mold species to answer the following:

    – How thorough was the cleaning (based on amount of outdoor molds settled over 2 weeks)
    – How thorough was the wipe sampling?
    – Do they grow in intermittent moisture, say from a rice cooker, or require a multi-week period of >90% moisture from a leak (e.g. Stachybotrys)?
    – Lastly, how similar is the pattern of species from before the remediation? That’s an important clue. If similar, it could be a problem of the remediation.

    So more problem-solving questions:

    1. How thorough was the investigation of the house envelope and checking for moisture sources, both visual and with an infrared thermometer or IR camera? (it’s frustratingly easy to miss some!).
    2. Was remediation done under appropriate containment with negative air pressure? Were remediators careful to not track mold on shoes and clothes? If not, mold fragments would have been aerosolized and distributed throughout the house when moldy sheetrock was removed and vacuuming/scrubbing was done.
    3. Were *all* indoor surfaces wiped with microfiber cloths after the HEPA vacuuming?
    4. Was the surface cleaning verified post-remediation? If not, some surfaces likely still have old mold spores and especially fragments mixed in with newer dust. [see Mycometer-Surface – https://www.mycometer.com/products/mycometer-surface/surface-sampling/%5D

    What makes an ERMI more valid than the air sample? That’s easy — because the latter groups Aspergillus/Penicillium species and doesn’t separate between the benign ones and the mycotoxin-loaded ones, and because the outdoor air “control” is so variable — over a day it could have 100-500 times more or less mold depending on the wind, barometric pressure, recent rain/drying period. So the same indoor spore count could be seen as “low” or as “problematic” depending on the time of day the outdoor sample was taken. So if an air sample is high, you know to keep looking. However, if it’s low, it may well be a false negative. In contrast, after a good cleaning (and verification) you need enough new dust to settle for an ERMI to show if there’s a continued problem. So it makes sense to me to do both — they give very different information.

    What about moving back in?

    It depends on the financial constraints and health of the family. Certainly it is much easier to investigate and re-clean before folks (and their stuff) move back in. However, *if* nobody in the family is sensitive to mold, and depending on which molds are elevated, folks could choose to move back, maybe simply re-wiping all surfaces. Some folks seem genetically resistant — so they don’t care. Still, it is a risk to consider — what if someone becomes sensitized in 3-6 months, say after influenza messes with their immune system?

    In our sensitized family we’ve learned the hard way that such a high ERMI means staying out — we didn’t re-test before moving back in, and all of our newly cleaned contents become contaminated again, and the person who’d been doing much better away from the mold became much sicker within a week, and kept getting sicker and sicker till we did new ERMIs (4 areas), realized the broad cross-contamination, and moved out again.

    As you said, air sampling and ERMI “give very different information”. The only correction I would have is in your sentence, “The ERMI formula uses logarithms, and a score of 22 means that some of those water-damage-indicator (Group 1) molds must have been thousands of times higher vs. the Group 2 molds.” That is not always the case. If you had 10,000 Group 1’s spread evenly among 10 types (sum of the logs is 30), and 10,000 Group 2, but just in one type (sum of the log is 4), your ERMI score would be 26 (30 minus 4) even though the total spore equivalents were the same. It’s a small change, but I would say that Group 1s “may” be thousands of times higher. Thanks for your comment. You clearly put in a lot of thought and time and I appreciate you sharing this information on our site.

    I hope your family can solve the mold issues and get better.

    I purchased a house in 2016, after 2 weeks of being in house my children all started getting sick. Along with my self. We got a air sample done our test results had over 248,000 spores inside the house and 0 on the exterior. We then learned that the house had been vacant for two years prior to purchase. To this day my children n myself have been sick and we had to move out of that house

    Thank you for commenting. I’m sorry to hear that your home has a mold problem.

    We don’t know what to do. We suspected mold in our home, and heard good things about the ERMI test, so we did the test and the ERMI score was off the charts at 28.06. We brought in a home inspector, and found a concentrated problem area, got it fixed, then vacuumed (HEPA filter attached) the whole house from ceiling to floor, and followed that by spraying a 50/50 mix of hydrogen peroxide and vinegar. We let the house sit for 2 weeks (we temporarily moved out), and then retested; this time with both an Air Sample and an ERMI. The Air Sample showed a moderate level of Penicillium/Aspergillus fungal growth inside the home (none was detected outside) at 350 spores/m3. We cleaned some more, and started to move back in the home. Then, we got the ERMI results back last night. The results were super high again, at 22. What should we do? One test tells us to move back in, while the other tells us to move out for good. Ha! Seriously though, we are confused. Any suggestions on how to find clarity with our situation? Thanks for any tips.

    Todd, We are in the preliminary stages and have just received an ERMI test of 29. We haven’t done an air test yet. We aren’t terribly ill, but I do have severe inflammation in my body (haven’t done a blood mold test). Most of my kids seem pretty healthy and my asthmatic-since-childhood husband is pretty stable as well. I did the test because I could smell mold daily, and especially acutely when I had been away from the house for a few weeks. Recently I came back and my children greeted me outdoors. They all smelled of mold to me! (I know, mold doesn’t have a smell, but you know what I mean). I’d like to hear how you progressed. I’m wondering if we should just move — which would be traumatic for all of us, especially my husband. Thank you for your insight.