If you’ve bought or sold a house in the 21st century, chances are good that you’ve had to read a mold report. Mold has become the latest bogey-man, leading to considerable (often unnecessary) concern and expense. But it’s become a fact of life that we all have to deal with, so I’m going to do my best to describe the reports so you can interpret them properly.
Before starting, be aware that this post does not contain a detailed discussion of mold varieties, allergies, cleanup, or other such details. There are numerous sites that contain that sort of information.
One caution – due to all the FUD (fear, uncertainty and doubt) there is a huge industry built around “mold remediation.” You will find countless websites of mold companies whose sole purpose is to sell you expensive mold remediation services. Their angle is often to prey on consumers’ fears. As such, you are advised to rely on independent sites for more accurate information on mold. Many states maintain mold awareness sites and have documents available that provide detailed information on how to clean and deal with mold.
Important: the information contained on this page is basic and simplified to ease understanding of mold reports. It does not replace mold reports or the use of licensed mold professionals. If you believe you have mold issues in your home, you should consult a local, licensed mold professional.
The Basics of Mold Tests
Note, as per the EPA website, “no EPA or other federal limits have been set for mold or mold spores, sampling cannot be used to check a building’s compliance with federal mold standards”
Two basic mold tests – air and surface. One tests the levels of airborne mold. The other samples suspected mold on surfaces.
Mold counts – mold tests boil down to simply counting the number and type of mold spores in a given amount of air or on a surface.
Reference counts – Most mold reports contain a “reference” mold test. The purpose of this test is to measure the mold in the air outside the home to use as a reference to compare with the mold inside the home.
Mold types – The report will contain a list of mold types. You can find considerable information on the web about each type of mold. A good starting point is Wikipedia.
“Raw count” – This column in the mold report shows the number of each type of mold spore that was counted in the sample provided to the lab.
“Count/m3” – This column estimates the number of mold spores that would be found in one cubic meter of air based on the “raw count” and the amount of air sampled.
“% of total” – This column computes the relative amount of mold measured for each species compared with all the mold found.
Comments on mold types
There are many types of mold. Some are generally beneficial while others create irritants and toxins that some people have reactions to.
All small particles – simple dust, pollen, mold, pet dander, smoke etc., can cause reactions in people. Often they’re simply an irritant. The important thing to know is that you are exposed to many molds in going about your daily life without any adverse effects.
For example, varieties of Penicillium mold are used in the production of cheese and cover cured sausage. In all likelihood, you’ve breathed or eaten mold recently!
The confusing thing is that mold tests usually provide no information about the types of mold and their relative ability to harm people. They also lump together all similar species. For example, you will find a line item listing “Aspergillus/Penicillium” because these are very difficult to differentiate. So a given single mold count could contain dozens of different types of molds.
Mold Counts
It is important to understand that mold levels outdoors vary throughout the year as they grow vigorously on plants and in woodlands. It is common for mold counts outdoors to be in the thousands per cubic meter. Read this again: it is common for mold counts outdoors to be thousands per cubic meter. It is very likely that you have breathed mold concentrations at these levels with absolutely no adverse effects. And yet, I have seen mold reports that flag these same, naturally occurring species, in big red letters “ELEVATED” when the counts are in the low hundreds.
It is also important to note that there are no mold standards published by the EPA.
Air-O-Cell(tm), the manufacturer of Spore Trap, on of the most commonly used mold tests, advises against comparing indoor and outdoor spore levels (page 6: IAQ Interpretation document). To quote: “A high variability in outdoor mold spore concentrations and distribution exists on a daily to hourly basis and is dependent on local vegetation and micro-climate, the time of year, local weather patterns, and diurnal variation. As a result, caution must be used when simultaneously comparing limited data sets of inside and outside concentrations or over generalizing any set of data.”
And yet, one of the most common testing labs providing mold reports, does exactly this – they flag mold levels based on comparing the indoor and outdoor mold levels. How much do you trust a report that flag results in direct contradiction to the instructions provided by the manufacturer of the test equipment?
Again, quoting from the Air-O-Cell document, there are several key numbers that you can use for comparison:
Typical outdoor mold spore concentrations: 50-50,000 depending on where you live. The range is low in the desert where the humidity is low and higher in the country, on farms or forests.
They also note a reference figure for a “clean” building to have less than 2,000 total counts per cubic meter with 700 or less of Penicillium and Aspergillus (the most common molds found in nature and homes) with counts of 5,000-10,000 typically indicating indoor mold growth.
This should provide you with the basic information necessary to understanding a mold report without being freaked out by it. Remember, mold is naturally occurring, often in very high levels. Most of us breath and eat it every day without any adverse effects. Interpret mold reports with open eyes – a red font and scary words in the report doesn’t necessarily mean that your child’s health is in jeopardy. Unfortunately, mold reports are often used to sell unnecessary services based on misleading information such as “elevated mold levels” compared to outdoors. Comparisons that even the manufacturer of the equipment advises against.
I encourage you to refer to the cited references for more information.
Mold resources
Mold Guidelines for New Jersey Residents
EPA Mold Information page
EPA guide to mold, moisture and your home
EPA information on mold testing
Air-O-Cell Method Interpretation Guide
Ted's Energy Tips 
At some point almost all buildings and especially homes will have mold, typically hidden behind walls, hidden forever never to be seen. No problem, no worries. Common sense would dictate that if you have black or green powder substance growing on the outside of a interior wall,. or you or family members start sneezing or coughing in a room, you likely have a problem.
So your point is, just don’t freak out???? Good advice, but not a long term solution to a problem. Air quality tests are a tool. That’s it. It’s to be used with common sense along with studying the history of the home, visual inspection, infrared inspection, and moisture meters.
There are currently millions of people nationwide that suffer from mold illness. It involves the toxins that are released when mold feeds on indoor materials that are dangerous, as well as the allergenic properties of the actual spores. I’m quite sure you are neither a healthcare professional or a microbiologist, so I would encourage you to not downplay or minimize a subject you don’t completely understand.
No, the point is don’t freak out, but take necessary precautions. If you have known sensitivities, obviously, you have to be extra careful. As you note, proper testing is important, as is remediation if it’s a real problem.
OTOH, if you just have some common mold in your shower, and you’ve never had any issue with mold in your medical history, just clean it up with soap and water and get on with your life.