ERMI Testing Vs. Air Samples

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.


EPA Website:

Joel Silva

Joel Silva

Joel Silva is a Project Manager that performs indoor air quality assessments with a specialty in mold and bacteria. Mr. Silva holds a Bachelors of Science degree in Biology from Aurora University. Prior to working at Indoor Science, Joel did microbiology work in the quality assurance department for a food manufacturer. During school, he also interned for the Chicago Department of Public Health. In his words... “As a child, I had an interest in science specifically in the biology of the natural world. Besides working for Indoor Science, I enjoy running outdoors, competing in races, lifting weights, practicing yoga, reading, and visiting breweries all over the country.”

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15 thoughts on “ERMI Testing Vs. Air Samples

    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.

    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*

    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.