ERMI Mold Test: A Comprehensive Guide to Dust Sampling For Mold

By: Licensed Mold Assessor Brad Fishbein

February 4, 2023

The ERMI test for mold is an acronym for Environmental relative moldiness index which is a collection of dust within a home that is sent to a laboratory for analysis. The lab screens the dust for 36 different types of mold species that are commonly found indoors by a method called PCR testing.

But how effective is an ERMI mold test?

It is certainly controversial in the mold industry and ERMI testing is becoming more and more popular. It's looked at as a new cutting-edge type of mold testing even though it has been around since the early 2000s.

Some people believe that ERMI is the only test that should be done while there are others that believe it's the only type of mold testing that should be done if a person is experiencing mold exposure symptoms in their home.

Many doctors are also advocates of performing an ERMI sample in a moldy home.

In this article, we will explore everything you need to know about ERMI sampling, and then you can determine if you would like to do this type of sampling for any mold problem you may have in your home.

How is An ERMI Test Done?

Typical mold sampling in a house usually involves something called a spore trap where the amount of mold spores are collected from the air and then analyzed under a microscope. Swab or tape sampling can be done on visible mold growth.

Instead of testing the air, ERMI testing tests the dust.


You can also collect dust samples and not have it called an ERMI test.

Let me explain...

You see the ERMI test isn't just looked at under a microscope like other mold samples. A method called quantitative polymerase chain reaction is done to extract DNA from the dust and test it for mold.

But how is the dust collected?

This is partially the controversial part but more on that later.

Laboratories recommend that dust samples be taken throughout the home. The samples can be collected using a cotton swab, or dust cassette, or you can even collect the dust and put it in a sealed Ziploc bag. It really doesn't matter.

Once the samples are collected they are then sent to whatever lab is contracted to analyze the samples.

Environmental Relative Moldiness Index Report

The dust is analyzed by a laboratory using a process called Quantitative polymerase chain reaction (MSQPCR). There are 36 different types of mold that are divided into two groups:

  • Molds associated with water damage or moldy homes (26 species)

  • Common indoor molds associated with normal fungal building environments (10 species)

Basically, the two groups are used in conjunction with each other using a math formula to come up with an ERMI score. The ERMI score in your home ranges from -10 (which is the best score you can have) to 20 (the worst score you can have).

The report will break down the different microbial species that were found and how much of them is present. You will also be presented with a final ERMI score. There is no specific passing or failing however obviously a higher score can indicate mold contamination in the home.

Who Does The ERMI Sampling?

While other types of mold testing are typically done by a mold inspector, the ERMI environmental relative moldiness index test, it can also be done by the building occupants.

The only work that actually needs to be done is the collection of dust.

No middleman or inspector is necessary


Where To Collect The Dust Sample For Mold Spores

Determining the location where dust sampling is performed is often the most overlooked aspect of ERMI sampling.

The reason why it's overlooked is the accuracy of the report depends on the location the dust is collected from.

Many laboratories recommend taking dust from multiple rooms in the home or even the entire indoor environment.

There is a big time problem with this recommendation that we will go over further in detail in just a bit.

You may find it challenging to collect dust in you your home, especially if you are a very clean person. Finding carpet dust or dust on furniture may not be easy for some people.


Here are a few areas where you can look for dust:

  • Behind furniture

  • Under couches

  • The HVAC return register

  • In the corners of the carpet

Controversies Of ERMI Testing

As alluded to earlier, ERMI testing does not come without controversies in the mold industry.

Here's the background of the ERMI mold test:

Many laboratories and other mold testing companies that make money off the test indicate it is Environmental Protection Agency (EPA) approved. That's not completely accurate.

You see:

The EPA did develop the test and this is 100% accurate. Many companies even promote the fact that it's EPA approved.

But what the companies that are selling laboratory services to test mold species for ERMI tests are not saying is that the EPA actually recommends AGAINST ERMI testing in homes.

ERMI was developed as a research tool for the EPA, and not to be commercialized. Not at least until peer review has been done.


Actually, peer review has been done and there are some issues with the ERMI mold test.

False Positive Of ERMI Testing

Dust samples are taken within the home, and the lab results may reveal a problem with the dust, however, it does not necessarily mean that there is a mold problem in the home.

Let me explain...

Mold spores are everywhere.

We carry them on our clothes, they are in furniture, shoes, etc. So just because mold growth is found in some of the dust, it could indicate it originated somewhere else and not an indication of a fungal problem in the home. Here's an example for you:


Let's say either you or another person in your home decided to go golfing the day before ERMI sampling was done in the home. And that bag was left outside and in your humid Garage in the months leading up to this day.

Well, there is a good chance that the bag will have mold growth on it whether there is visible mold or not.

And if that bag was brought into the home, it's very possible that some mold spores may have cross-contaminated from the bag into the home.

The ERMI sample may indicate there is a problem and the occupants may have mold exposure in the home, but that would be inaccurate. The bag had a problem with mold and now you think there is a microbial problem and may even hire a costly mold remediation company to do work in the home that is not necessary.

Talk about an overreaction!

Determining Where The Mold Problem Is

The biggest issue with the ERMI sample results is unless it's done in every single room, it's not really useful.

If you collect dust from the entire home and it comes back showing toxin-producing molds are present, how can you determine where the problem is located?


The correct way to do it would be in each and every single room and determine which one of the rooms have biotoxins found. That way, you can hone in on that location and see if there is some kind of water damage that can be found producing mycotoxin-causing mold species that can have health effects.

But again as we said, the spores may have also been brought from an outside source.

ERMI Testing Doesn't Test For All Types Of Mold Species

Remember how ERMI lab testing only tests for 36 types of mold? Well, there are hundreds of thousands of species of mold.

Yes, The ERMI test checks for the index number of the most very common types of spores in an indoor environment, but the problem with that is certain molds are found in certain climates.

That means you may not find the same species of mold that you find in Florida compared to Colorado.

The EPA originally only tested a handful of homes in Ohio and based the 36 species of mold on what was found in those samples alone.

Is ERMI The Best Type Of Mold Sampling?

While many mold companies and laboratories push ERMI testing as the best and most accurate type of mold sampling.

It's not a one size fits all with mold.

There are limitations to every type of mold sampling. It's not necessarily ERMI sampling vs air sampling. In a way, they both serve different purposes. ERMI sampling is more designed to determine the history of the home and what can be in the settled dust whereas air sampling is better at determining the current air quality conditions of the home.

What it comes down to is what is the best type of quality for you and your home. If you know you have mold problems and have visible mold growth, it needs to be properly remediated.

In a perfect world, you would want to do all sorts of different types of microbial sampling but the budget does come into consideration.

How Much Does ERMI Testing Cost

The cost of the ERMI test really depends on who is doing it. If you are paying a mold professional to come into your home and collect dust samples, you will obviously pay a premium to have them do the work.

In regards to the laboratory fees, you can expect to pay anywhere from $250-500.

Should You Do The ERMI Test?

Determining whether you should do ERMI sampling for mold or a different type on sampling method is really going to be up to what you are looking to accomplish.

Many doctors will recommend ERMI, so if your doctor is one of them, you should listen to them.

Either way, you should have a complete home mold inspection if you suspect you have a mold problem in your home.

Meet the author: Brad Fishbein is an ACAC council-certified Microbial Investigator. In the fall of 2012, he became a Licensed Mold Assessor in the State of Florida through the Department of Business & Professional Regulation. Brad has helped homeowners with over 5,000 successfully completed Mold Inspections since 2009.

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