In my last 2 articles/podcasts, I discussed the most common symptoms of mold exposure to look out for, and how to test yourself for mold exposure.

Today, I’m going to dive into testing your home or office environment.

If you have symptoms, and/or have tested positive for mold and mycotoxins, the next step – after starting to work with Dr. Emily (or another mold-literate practitioner) to formulate and begin implementing your treatment plan – is to investigate your surroundings to answer this crucial question:

Where did the mold come from?

At this stage, if you don’t know where the mold came from and suspect it could be from your current home or work environment, then mold inspection of your home and/or office, and remediation if indicated, is absolutely essential.

Because without proper identification and effective, thorough remediation of the source of your mold exposure, continuing exposure will likely happen, and will make full recovery much more difficult.

Testing Methods

There are 5 main mold testing methods:


Gravity Plates

A popular method of environmental mold testing is gravity plates, also known as petri dishes, settle plates, or Gradient Agar Plates. This testing method uses a specialized gel which sits on a plate, and collects and grows a sample of mold spores from the air. Gravity Plate testing facilitates easy and inexpensive passive testing of air quality for as few or as many rooms or areas as desired, including cars (a surprisingly common source of mold exposure!)

However, plates can only capture a limited group of spores (i.e., the ones closest to the plate, the ones most likely to be airborne, and the heaviest ones that are more likely to settle onto the plates), and not all types of mold will grow on all types of media, many spores and types of mold will often go undetected when testing using plates. You just won’t get a clear picture to be able to determine if the sample is or isn’t representative of what is going on in your environment.

The volume of mold growth on a plate is not indicative of anything beyond how fast that particular spore grows in the type of culture medium provided on the plate. The color of the mold on the plate is also irrelevant, as mold color alone cannot be used to determine type, quantity, or toxicity.

What else your plate or mold test kit won’t tell you:  

  • What spores are responsible for either the visible mold you are seeing and/or the symptoms you are experiencing. You don’t know if it is the spores that were detected or the ones that were undetected that are causing issues. 
  • If you have spores that don’t grow on plates. They can still trigger reactions, but won’t be detected by settling plates, and can outnumber spores that do grow by as much as 50x.
  • If you have fragments of spores and of growth, which can also trigger reactions and can be as much as 1000x more plentiful than what grows on a plate.
  • If the mold is producing mycotoxins or other mold toxins.
  • The location of the mold growth that is producing the spores. Without that information you can’t know where to remediate.

So, are the results from plates useless or misleading?

Well, while they are not proof of a problem (or lack thereof), and can’t determine if action is needed, the results from settling plates can often be sufficient to trigger further investigation with an on-site assessment, which can then provide the rest of the information needed to answer your critically important questions about necessary next steps. In other words:

  • If the mold plate test looks bad, you definitely have more investigation to do.
  • If the mold plate test looks good, you might still have a mold problem and need to do more investigation.

Mold testing with plates is NOT accurate enough to rely upon as the sole method of testing. If you’re going to use settling plates to test for mold, make them merely one step in a comprehensive assessment.

Direct Examination

Another type of mold testing is direct examination, which allows for the immediate determination of the presence of mold spores, as well as what types of mold are present. Tape and swab sampling are the techniques typically used for direct examination. Direct examinations should only be used to sample visible mold growth in a contaminated area, since most surfaces collect a mixture of mold spores that are normally present in the environment.

Tape Sampling

Tape sampling is the most common technique used to test surfaces for mold during a mold inspection. It provides valuable information, as the species of mold, the relative degree of contamination, and the potential for airborne spore production may all be determined by tape sampling.  

Advantages of Tape Sampling
  1. Tape sampling is quick and easy.
  2. It is inexpensive.
  3. It requires no set-up time.
  4. It requires no complex equipment.
  5. Many samples can be collected in a short period of time.
  6. Samples showing hyphae fragments and reproductive structures can provide proof of mold growth.
  7. Tape sampling allows for the quick identification of genera and species by a laboratory.
  8. Tape samples provide more data than air samples.
  9. Tape sampling is usually non-destructive.
  1. While tape sampling is an excellent way to collect samples where mold is easy to see, light-colored and highly airborne genera, such as Aspergillus and Penicillium, may not be as obvious and can be missed using only tape sampling.
  2. Some smaller, airborne mold spores do not readily settle onto flat surfaces, so tape samples may not accurately represent their presence.
  3. If a tape sample is collected from dust rather than an area of actively growing mold, or if the sample is taken at the most spore-packed part of a growth area, it is possible that only spores will be collected.  This can make determination of the species more difficult.
  4. Using tape of any kind on certain types of materials, such as paper and varnished wood, may damage the item.
  5. Tape sampling is meant to be used for qualitative rather than quantitative analysis.  Tape sampling can aid in the identification of mold, but cannot accurately determine the scope and severity of the mold problem.
Swab Sampling

When there is visible mold, surface sampling by collecting mold samples with a simple swab test combined with lab analysis can determine if mold is present at amplified levels and exactly what type of mold you are dealing with. The lab analysis from the swab can pinpoint the type of molds present, many of which are not easily detected in air samples, such as Stachybotrys and Chaetomium (two of the most common and most health-destructive molds present in mold-contaminated buildings).

Swab sampling can help to identify sources of mold so that they can be addressed via basic clean-up or full-blown remediation. Swab sampling can reach deep into recessed corners, into carpets, and in many other areas that are difficult to test with tape sampling. One area where swab testing is particularly enlightening is heating and cooling system air handlers. Determining whether visible discoloration, dust, or debris seen on condensers and on HVAC registers is mold growth will provide important information about the path forward for the proper cleaning of the HVAC system.

Spore Trap

Spore trap samplers function by pulling air through a sample slit and onto a small glass slide that is covered with a sticky sampling media (like flypaper or a glue trap).

spore trap sampler

Advantages of Spore Traps
  • Capable of capturing a majority of spores and particulate matter in the air, making it possible to accurately characterize problem environments where spores are present, including those that are no longer alive, or are species that do not culture well. (These are two situations where culturable sampling techniques, if used alone, may miss a potential indoor air quality problem.)
  • Can also be used to quantify pollen, fiberglass, hyphal fragments, hair, skin cells, etc., present in the air.
  • Samples can be analyzed immediately.
  • While many mold spores have unique characteristics and can be identified by direct microscopic examination, others do not and are thus more difficult to identify. These latter types must be counted in broader spore groups. In certain situations, this grouping may mask an indoor air quality problem.


The Environmental Relative Moldiness Index (ERMI) uses the analysis of settled dust in homes and buildings to determine the relative moldiness of that environment. The ERMI uses a mold-specific quantitative polymerase chain reaction (MSQPCR) – a fast and highly accurate DNA-based analytical method for identifying and quantifying dozens of different types of molds. MSQPCR methods can determine both the genus and species level of molds, and from there, your environment’s ERMI score is then calculated. The range for the score is -10 to 20, -10 being the lowest moldiness level and 20 being the highest.
The ERMI is considered by many to be the most accurate and comprehensive choice for mold testing. The ERMI was developed by the US EPA, and is available from many mold testing companies – search “ERMI” online to find options. I and many of my patients have used the EnviroBiomics ERMI and been very satisfied with their customer service, reporting, and level of expertise.


A subset of the ERMI, the HERTSMI – Health Effects Roster of Type-Specific Formers of Mycotoxins and Inflammagens – tests for just 5 species of mold, vs the 36 species that the ERMI tests for. The HERTSMI test can identify the presence of “the big 5” molds:

  • Aspergilus Penicilloides
  • Aspergillus Versicolor
  • Chaetomium Globosum
  • Stachybotrys Chartarum
  • Wallemia Sebi

Because it is more limited, the HERTSMI test is less expensive than the ERMI. Often, the HERTSMI will be used at the end of remediation efforts, to determine if an environment is safe to re-inhabit, if the initial ERMI test indicated the presence of only some or all of these 5 molds.

Professional Home Inspections

If you aren’t sure how you’d like to proceed with testing, or if you have done some of the above testing and it indicates mold in your environment, then having a mold testing professional come out and test your environment is a wise next step. To find a qualified professional, visit National Association of Mold Remediators and Inspectors (NAMRI). This organization is dedicated to ensuring professionalism in the mold inspection and remediation profession. Inspectors associated with this group are held to a minimum requirement for describing and reporting microbial overgrowth and contributing factors. Members must have a minimum of 90 hours of accredited mold education training, have completed at least 25 mold inspection or remediation jobs, and have passed a mold testing exam.

Summing Up

In the journey of mold-related illness, finding the source of exposure is a crucial part of the puzzle. When it comes to choosing tests or inspectors, it can be overwhelming! I hope this guide has helped you to better understand your options, to make it simpler to navigate the choices that are out there.

Next Steps

If you think you might be dealing with mold illness, or would like more guidance on steps to take to deal with mold, and would like to talk with a mold-literate practitioner about your situation, book yourself a consultation (if you’re an existing patient) or a free initial phone call (if you’re a potential new patient) with me via my online calendar at