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More on the Interpretation of Mold Air Samples

test results; mold air samples; confusing

Are you staring at the results of mold air samples and struggling to figure out what it all means?  Let me try to help you.

The most common method used for mold air testing is uses a spore trap cassette. Because there is always a background amount of airborne mold spores, a key step in collecting air samples is to have a “reference” sample collected from the outdoor air at the time of the indoor testing. Since there are no guidelines on acceptable mold levels in the air, an outdoor sample is the best tool for interpreting the results of the indoor samples. Without the outdoor sample, you are limited in what you can gather from the results of the indoor samples.

There are various D.I.Y. air tests you can pick up at your local hardware store requiring you to place out a petri dish for several hours. Most of those tests are not very helpful in giving you any sort of usable data to evaluate the air in your home and as a general suggestion should be avoided.

Interpreting mold levels can be tricky. If you would like feedback on your mold air sampling results, please comment below and I will do my best to give any feedback I can in my free time. The views expressed in the blog post and comments are my own, and not necessarily those of Indoor Science. If you need a more immediate response regarding your results you can book a 30-minute phone consultation for $98 by clicking here.

Dylan McIntosh

Dylan McIntosh

Dylan McIntosh is a Senior Project Manager that performs indoor air quality assessments, industrial hygiene testing, and laboratory mold analysis. Mr. McIntosh holds a Bachelors of Science degree in Biology from the University of Illinois - Springfield. Dylan is a Certified Industrial Hygienist (CIH) and an Pan American Aerobiology Certification Board (PAACB) Certified Spore Analyst. In his words… “Throughout my life, I always had a dream of becoming an astronaut. That dream hasn’t worked out (yet) so I started a career in the next best thing, indoor air quality! In my free time I enjoy outdoor activities with my dog, cooking, and being involved with A Special Wish - Chicago; a local charity.”

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512 thoughts on “More on the Interpretation of Mold Air Samples

    Hi Dylan,
    This is incredible that you are willing to help so many of us on your blog, thank you!! Here are test results. We’d appreciate hearing your insights on our two samples:
    SAMPLE ONE (Raw count/ spores per cu m / %) obtained after mold remediation
    Basidiospores: 6/240/40%
    Cladosporium: 5/200/33%
    Mitospores: 2/80/13.33%
    Pen/Asp group: 2/80/13.33%
    Basidiospores 1/40/50%
    Chaetomium 1/40/50%

    SAMPLE TWO (after separate water intrusion in another part of the home with high debris but very low hyphal fragments and pollen)
    Cladosporium: 14/560/40%
    Basidiospores: 9/360/25.7%
    Smuts/Periconia/Myxomycetes: 16/240/17%
    Ascospores & rust: 2/80/5.7%
    Epicoccum nigrum & Pithomyces: 1/40/2.86%
    Inside bedroom:
    Basidiospores: 5/200/41.67%
    Ascospores & Curvularia: 2/80/16.7%
    Cladosporium & Mitospores & Pen/Asp group: 1/40/8.33%


    The basement sample in the first test has a small amount of Chaetomium present. This is a water damage indicator and also a potentially toxigenic fungus. Some inspectors would not pass a remediation project with even a single spore of Chaetomium, but others would. It is a bit of a middle area, and should be a “yellow flag” to you. Meaning, it is not something immediately alarming but something to keep a note of.

    The second test looks all good.

    That’s what we were thinking too. Thank you so very much. We really appreciate your feedback. This community service that you are doing is invaluable!!

    Hi Dylan,
    I had the test done once and the results were:
    Outside Building: 125.2 MAV/m3
    Resident’s room: 134.4
    I would love to hear your opinion on the results, especially since the people who did the testing , when they sent me the report of the results, they mistakenly sent me a word document with their edits still present. The original author had indicated the “The indoor and outdoor results are above normal background levels which could indicate high dust spore levels or old fungal growth” But then her review completely did a 180 and changed those lines to “The indoor and outdoor results are similar which indicate there isn’t a significant source of mold”.
    I wonder if the original author was novice and genuinely wrong, or the boss was a little dishonest, and trying to avoid any liability.
    I truly appreciate your time,



    I am not familiar with mold air sample results in this format. Typically results are reported in a way that identifies the type of mold present and the concentration (spores/m3) in a whole number (the laboratory protocol does not calculate fractions of spores).

    Hello, we have been dealing with new construction, high humidity in our house, very high mold counts in the past, and a few sessions of professional mold remediation. Should I be concerned with the latest test results? I hope that we now have it down to an ok level, but We have kiddos and I am allergic to mold so I just wanted to make sure. Thank you!
    Results are in spores per cubic meter (s/m3) Detection Limit = 13 spores s/m3 ND = Not detected
    Sample Basement near electrical panel Basement near hvac Living Rm Master BR Hallway Outdoors
    Alternaria 13 ND ND ND ND ND
    Ascospores 67 80 427 107 53 5,360
    Aspergillus/Penicillium 320 267 27 80 27 ND
    Basidiospores 187 107 933 133 67 3,867
    Cladosporium 40 27 ND 40 ND 613
    Curvularia ND ND ND 13 ND ND
    Epicoccum ND ND ND ND 13 67
    Smuts/ Myxomycetes ND ND ND ND ND 40


    The asp/pen levels in the basement are slightly elevated but are within the range we can see in the outdoors. Since I am a medical professional, I can not assess if these levels are enough to cause health effects in you and your family, but I can say that you are exposed to similar levels in the outdoors fairly frequently in the warmer months.

    Hi Dylan! My son and his wife are looking to purchase a home in Pueblo West, Colorado. It was a rental house previously and the last tenants had a marijuana grow in the basement. As part of the inspection they had a mold test performed. The basement is unfinished and is about 1300 square feet. The results were:

    Raw count 7
    Spores/cubic meter 47
    Percent of total 41.

    They’ve asked the seller to remediate and retest after, but don’t know that she will. Our question is whether this is a small, moderate, or large amount of mold. They’re just starting out, and if she won’t do it they’ll have to do it themselves they think as they can’t afford to pay someone else to do it.

    Thanks for any guidance you can give to us!

    Chaetomium is a water damage indicator, while these numbers are not off the charts, they are an indication of growth. Addressing mold of this level in an unfinished basement should not be a major undertaking, but they should keep an eye out for any moisture problems in the basement going forward.

    Thanks for your response. They think the water damage came from the marijuana grow. They were watering with a garden hose, didn’t have a sophisticated watering system. Appreciate the information.

    With this level, do you think they could do the mitigation themselves? The only wood is in the ceiling and in the staircase support, everything else is cement.

    I was wanting to know what you would think if this test I received from my apartment. This was done after smelling a musky odor for two years and complaining. They finally did this test after asking several times; this is also a small apartment one bedroom no more than 790 square foot.

    Spore type. Raw count. Count/m3. %total
    Ascospores. 17 750. 40.1
    Aspergillus. 7. 300 16
    Basidiospore. 15. 660. 35.3
    Cladosporium. 3. 100. 5.3
    Curvularia. 1. 10. 0.5
    Myxomycetes. 1. 40. 2.1
    Pithomyces. 1. 10. 0.5


    Without an outdoor control sample, I really can not interpret these results in any meaningful way. It does not appear that there is a major mold issue, but without that reference sample, that’s all I can deduct from this data.

    Dear Dylan,

    I am dealing with a chronic illness and because our basement floods regularly, we believe we have quite a serious mold problem at home. While we have not yet had it tested, we have been looking for another home to move into for health reasons and have made an offer on a house (that was accepted) and was tested for mold.

    These were the results:
    raw ct/per m3
    Outside: Basidiospores 213/5700
    Cladosporium 43/1,100
    Penicillium/Aspergillus types 13/350
    Others 62/1,700
    Total count: 8,800

    Verses Inside (Living Room)
    Basidiospores 101/2,700
    Cladosporium 38/1,000
    Penicillium/Aspergillus 51/1,400
    Others 56/1,500
    Total count: 6,600

    Do these results indicate that there is a mold problem in the house? Windows were open when test was performed, so I don’t know how that impacted the results. I realize there are many factors that can skew the results. Your perspective is much appreciated (and sooner rather than later, as we have to make a decision about the house soon). Thank you very much.



    These results do indicate an elevated level of mold in the home. The Cladosporium and Asp/Pen levels in the living room are elevated. Mold testing should always be done with windows closed, preferably for at least 24 hrs before the testing.


    Thank you SO MUCH. This is tremendously helpful. Are there any other things we should know so we get an accurate test? We will likely be redoing the air sample testing. In the report, it noted that there was also a houseplant, which could have affected the Pen/Asp results. Thanks!


    Usually, a single houseplant isn’t going to affect the levels too much, but if you live in an indoor jungle it definitely could!

    ACGIH suggests a series of 3 air samples, one outdoors, one in the area of concern, and another indoors in an unaffected area. Another crucial part to a mold inspection is having someone check for moisture.

    Hi Dylan,

    Recently received test results from a mold test performed on a home we are planning to buy. I do realize that many types of mold are commonly found in the air naturally but our Penicillium/Aspergillus came back high. Raw Count=1,357, Spores/m3=9,092.

    All other types detected were in the single or double digits, under 100 so these are quite high in my opinion. Trouble is, no visual evidence of mold was found in the basement, home, or attic. What are your thoughts on possible causes for levels this high? The home does not have an HVAC system, only baseboard heat and the oil tank is stored in the basement. It is occupied, the current owners do have pets. The home overall appears to be clean and there is no musty smell anywhere. Any advice on where to look for the source is greatly appreciated!


    I learned that the sellers of the home had the old carpet in the living room torn up an replaced less than 48 hours before our mold test was conducted. The test was done in this same room. Could this be a reasonable explanation as to why we received results with these elevated levels? Seller plans to have mold mitigation company fog the area to kill the mold and then re-test. What is a reasonable amount of time to give before re-testing to give an accurate reading?


    Fogging will not remove the mold from the environment, so even if they fogged the mold would appear on the air samples. Fogging is not a method supported by any of the industry standards for mold remediation. The air should be filtered with an air scrubber, and surfaces in the areas should be cleaned, this would remove the mold from the air and what has settled onto surfaces. You would want to run air scrubbers for a few days before retesting.


    That level to me is indicative of some underlying mold issue. It could be that there was a past moisture event and mold was never remediated, for example the basement flooded, they dried everything out but kept carpet and padding in place. There are countless hypotheticals like this, but I would bet there is some hidden mold growth somewhere, as these levels are too high to be “normal” from the outdoor air.

    Hi Dylan, we had a leak in our basement over a year ago and let it dry out. There were no visual signs of mold but over time we began to be concerned it may be there and we’re not seeing it. Was just curious what you think of these results below? We have decided to get it remediated. Luckily, we spend almost no time in our basement.

    I’ll do raw count/spores m3 below in basement vs. outside baseline.

    Ascospores – BASEMENT 12/156 OUTSIDE 3/39
    Basidiospores – BASEMENT 66/858 OUTSIDE 15/195
    Cladosporium BASEMENT 45/485 OUTSIDE 1/13
    Pen/Asp BASEMENT 615/8000 12/156

    That’s pretty high on the Pen/Asp, right? What about the others? Thank you very much for any input you have.


    The Pen/Asp is pretty high. Not off the charts, but definitely elevated. Id suspect you likely have some humidity issues in the basement, beyond the water leak you had. After remediation, it may be smart to keep a dehumidifier in the basement, as environments with an RH above 60% can have mold issues without additional water sources.

    Hey Dylan, thank you so much. That’s super helpful. We definitely have a RH at 55% or above during the warm months (we’re in Massachusetts). In the winter, even if I set the dehumidifier to 30-40%, it wouldn’t run which tells me that it’s dry there in the winter. That said, if we weren’t running a dh during the summer months, could mold grow/exist during the warm months and just stay over the winter? Or, does it need moisture in the air to grow/survive the winter months were the humidity levels drop a lot? Again, your answer was super helpful – thank you for that.


    In the winter there are unique concerns with humidity. When the air is very cold we can have condensation on surfaces with RH levels below 60%, typically we suggest maintaining a level around 30% during freezing weather.

    Mold is very resilient. If it were growing in the elevated humidity of the summer but did not have moisture in winter, much of that mold would survive until summer returned. It would stop growing and reproducing in the absence of moisture, but when it returned the mold would become “active” again.

    Hi Dylan,

    I was looking at purchasing a home and was told there was “some mold found”. These are the highlighted ones in the report. Owner said it never flooded and there was a small leak from the water heater.

    Chaetomium 0
    Pen/Asp 148/1920
    Stachybotrys 0

    Kitchen W Wall
    Chaetomium 65/845
    Pen/Asp 8200/107000
    Stachybotrys 3/39

    Master Bath
    Chaetomium 67/871
    Pen/Asp 18000/234000
    Stachybotrys 13/169

    Living Rm W Wall
    Chaetomium 7/91
    Pen/Asp 5400/70200
    Stachybotrys 9/117

    After seeing everyone else’s numbers, these seems way off the chart. What do you think?




    Yes, these numbers are very high. This is an indication of a large and long term water issue, I would not expect levels this high from only a leaky water heater.

    Thanks so much for your help it’s much appreciated!

    I have some questions – we’ve had water damage in our home due to bad old gutters for years. We’ve had a bunch of testing done and have found different levels of moulds in different rooms – mostly Cladosporium. Except for our reverse cycle aircon swab which came back with high reading of 2000 asco 5000 clado and 10,000 ulocladium plus hyphal fragments 21,000 despite being cleaned 6 months ago.. I always didn’t feel well when it’s on but the rest of the family felt fine. I’ve had a mould blood test that shows I have a sensitivity or inflammatory markers however they measure it. Im guessing these results are pretty bad in the air con?? I’ve looked outside and it looks like one of the hoses may be blocked to the outside system. We also don’t use the ducted heating anymore as I always felt terrible when it was on and have found out in our subfloor test that it had Cladosporium 720 so am thinking it’s been blowing mould all thru the house whenever on – the ducts were left just lying on the ground a poor installation job..

    The main thing to ask about is I am confused about the difference in results in a same room our study which is used a bedroom – where a swab was used and an air sample used. The swab was taken on the floor against a wall which on the other side of that wall is the bathroom cupboard where at the back moisture has been detected and a swab from there came back 282,000 clado 500asco 2000 basid 500 epico 500 gando hyphal 1900.

    These are the swab/air sample results all in m3
    Study – swab
    Asp/pen 6720
    basidio 80
    asco 80
    clado 160
    smut 80
    hyphal fragments 80
    it also says underneath results detection limit 80 – not sure what this means??

    Study – air sample
    asco 27
    asp/pen 80
    basi 80
    clado 213
    curvularia 13
    rust 13
    smut 40
    hyphal 67
    pollen 13
    debris rating 3
    detection limit 13

    outside control
    asco 53
    basid 27
    clado 40
    pollen 13

    An air sample of the next bedroom over had results that were pretty similar to the outside sample.
    So if you can please help me interpret those results?? am confused because the swab seems to be a lot more serious than the air sample. also am considering putting my son in there who has sinus issues which is why I got it tested and now not sure if a bad idea especially with the hyphal fragments indicating growth in there (no hyphal fragments in the other bedroom)


    A swab detects the amount of mold growing on a surface, an air sample detects the level of mold floating around in the air. It is not always the case that surface mold growth causes an air quality issue, which is why the results are different for the swab and the air samples. Below the limit of detection is a fancy way the laboratory says “none”. The air sample result you attached appears fine, but the presence of mold in the HVAC and other surfaces is concerning.

    Hi Dylan,

    I hope that you are doing well. We are a first time home buyer in the Charleston, West Virginia area and recently received the mold air analytical report on the property in contract. Would you be kind enough to review and let me know your thoughts on whether you see anything concerning?

    The sample was taken in the afternoon. It did rain quite a bit the previous day and the outside front and back lawn were still damp from the rain water. The house is a 4 story and the inspector took two samples: one from the outside and one from the inside living room area. The results are below:

    Volume sampled 150L
    Media: Allergenco D
    % of trace Analyzed 100% at 600X magnification

    Outside Sample
    Ascospores – Raw Count 57 – Count/m3 380
    Basidiospores – Raw Count 693 – Count/m3 4,620
    Cladosporium – Raw Count 10 – Count/m3 67
    Smut/Myxomyces/Periconia – Raw Count 5 – Count/m3 33

    Total Spores: Raw Count 765 – Count/m3 5,100
    Debris Rating 3

    Living Room Sample
    Aspergillus/Penicillium-Like – Raw Count 23 – Count/m3 153
    Basidiospores – Raw Count 335 – Count/m3 2233
    Cladosporium – Raw Count 25 – Count/m3 167
    Smut/Myxomyces/Periconia – Raw Count 10 – Count/m3 67

    Total Spores: Raw Count 393 – Count/m3 2,620
    Debris Rating 4

    One thing to add, the inspector did not see any visible mold present in any part of the house. The only thing that was visible was a little moisture present in the garage back wall which is the basement and the foundation is present there. The water seems to be coming from above the wall where the back patio is. There is not adequate flashing installed on the vinyl siding and door frame which is allowing water to seep throught when it rains. There is a draining system present and installed along the bottom of the foundation walls to capture any water and drain it to the drain system. No visible mold or funny odor was present in the garage/basement area.

    I was curious to see Aspergillus/Penicillium detected in the living room sample and not the outside sample. Also, the Cladosporium sample from the living room had higer number than the outside sample. Would you be kind enough to share your thoughts on the samples results? Are any of these components worrying?

    Best Regards,


    These samples appear normal to me, the Asp/Pen levels are relatively low and at the level, we would expect to see indoors, same thing with the Cladosporium indoors. We can see both of these types up around 1000-1500 at times naturally.

    We had a Spore Trap Analysis done at our home. The technician looked through each room in the house and then went downstairs and ran the Spore Trap Analysis. The results came back today.
    Analylsis”: Chaetomium raw ct. = 1 per m3 = 13
    Cladosporium raw ct. = 2 per m3 = 110
    others raw ct. = 19 per m3= 1,000
    hyphal fragments 53
    skin cells 4,000-8,000
    pollen 53
    background debris (1-4) 3

    That is A LOT of skin cells for a spore trap. With that much debris it is likely the actual level of the mold in the air was obstructed on the sample. There is some water damage indicator mold present (Chaetomium). I would suggest doing a detailed cleaning of the home and retest.

    Hi Dylan,

    We are looking at buying a home and come to find out the attic was about 75% mold. The seller had a company come in and take care of it. I then hired Mold Remediation to come and inspect the attic to make sure it was done completely. He said the attic looked good and he didn’t see anything. He did an air test in the upstairs bedroom and the counts are:
    Pen/Asp Raw 73 – 3950 Spores/Cu.m
    Cladospourium Raw 18 – 960
    Basidiospores Raw 4 – 213
    Smuts/periconia/myxomycetes Raw 2-107
    Total Raw 98 and spores/Cu.m is 5230

    The outside tested 0

    What are your thoughts on this especially the Pen/Asp?

    Thank you so much,


    Those Pen/Asp levels are high. It is likely there is more work that needs to be done to remove all of the mold in the home.

    Hi – We are currently purchasing a home and have used two companies to do a mold test for comparison and I wanted to get your thoughts.

    Company 1:
    Test – Air-O-Cell
    Outside Sample
    Alternaria – Count 2 – Spores 16
    Aspergilus/Penicillium – Count 4 – Spores 32
    Basidiospores – Count 16 – Spores 128
    Chaetomium – Count 1- Spores 8
    Cladosporium – Count 15 – Spores 120
    Nigrospora – Count 2 – Spores 16
    Rusts – Count 5 – Spores 40
    Smuts/Myxomycetes – Count 1 – Spores 8
    Stachybotrys 1 – Spores 8
    Total Count 47 – Spores 376

    Inside Living Area
    Aspergilus/Penicillium – Count 23 – Spores 184
    Basidiospores – Count 12 – Spores 96
    Chaetomium – Count 1 – Spores 8
    Cladosporium – Count 13 – Spores 104
    Oidium/Persospora – Count 1 – Spores 8
    Rusts – Count 2 – Spores 16
    Totals – Count 42 – Spores 336

    Company 2
    Test Micro-5
    Outside Sample
    Alternaria – Count 3 – Spores 120
    Ascospores – Count 3 – Spores 120
    Basidiospores – Count 113 – Spores 4520
    Cladosporium – Count 84 – Spores 3360
    Epicoccum – Count 1 – Spores 40
    Penicillium/Aspergillus – Count 2 – Spores 80
    Total – Count 206 – Spores 8240

    Inside Living Area
    Alternaria – Count 1 – Spores 40
    Basidiospores – Count 27 – Count 1080
    Cladosporium – Count 52 – Spores 2080
    Penicillium/Aspergillus – Count 80 – Spores 3200
    Stachybotrys – Count 1 – Spores 40
    Total – Count – 162 Spores 6440

    I’m located in Arizona. I wanted to know your thoughts of these results and why there seems to be such a big difference between results. Thank you!

    I can not say why the numbers are so different, except that maybe they were collected from different areas indoors?

    The first company has some very interesting outdoor results. Chaetomium and Stachybotrys are almost never found in outdoor samples, and I can say I have never seen both of them together on an outdoor sample like this.

    The Asp/Pen levels from the second company are pretty high, they also found Stachybotrys which is a water damage indicator. I would say that there is possibly some history of moisture issues in the property.

    I hope you are doing well. We are currently in the process of purchasing a new home and mold remediation has been completed several times. Does anything about the numbers below concern you?
    Cladosporium Spores: Raw 8, 53 Spores/m3 (same as outside)
    Penicillium/Aspergillus group spores: Raw 51, 340 Spores/m3 (outside 6.7/m3)
    Aureobasidium spores: Raw 15, 100 Spores/m3 (outside 20/m3)
    Epicoccum Spores: Raw 3, 20 spores/m3 (outside 13/m3)
    Nigrospora spores Raw 1, 6.7 spores/m3
    smuts/periconia/myxomycetes: Raw 5, 33 spores/m3 (outside 20 spores/m3)

    Our total spores/m3 is 550 vs outside of 120.

    Thank you!


    In my opinion, these numbers look okay. The Penicillium/Aspergillus levels are slightly higher than outdoors but below the level that I typically see in areas with a major issue.

    Thanks for doing this!
    We just tested for mold after having flooding last year (downstairs was gutted, aired out, and rebuilt). The company wants us to fog and get an air scrubber (about $1200 total). Do you agree?

    Ascospores 1 Raw Count 30 Count/M3 11.1% of Total
    Aspergillus/Penicillium 3 Raw Count 90 Count/M3 33.3% of Total *This is the one they were concerned about
    Basidiospores 2 Raw Count 60 Count/M3 22.2% of Total
    Cladosporium 1 Raw Count 30 Count/M3 11.1% of Total
    Myxomycetes++ 2 Raw Count 60 Count/M3 22.2% of Total

    Aspergillus/Penicillium 1 Raw Count 30 Count/M3 50% of Total
    Cladosporium 1 Raw Count 30 Count/M3 50% of Total

    Thanks again!

    Hi Dylan,

    Hope you can help interpret an indoor air quality report performed on my son’s home which had extensive water damage to the first floor and basement of his ranch home. A malfunctioning dishwasher ran for approximately 5 hours while no one was home. Part of the report included a chart entitled “Total Fungal Genera Chart (Spores / m3)” at the top and numbers at the bottom starting at 0 and increasing by 5 up to 35. The rooms/areas tested were listed on the left with a colored bar chart and an associated number (indicating the number of spores per cubic meter??). He has lived in the home for 3 years. His wife is currently pregnant and they are concerned about the test results. The results are as follows:

    Master Bedroom
    Basidiospores 13
    Aspergillus / Penicillium 27

    Hallway at Bedrooms
    Cladosporium 20
    Basidiospores 7

    Living Room
    Ascospores 7

    Kitchen / Dining room
    Myxomycetes 7
    Cladosporium 13

    Basement SE Area
    Ascospores 13

    Basement SW Area
    Cladosporium 13

    Basement NE Area (Seems like a major issue here? Location of water meter)
    Chaetomium 7
    Bipolaris / Drechslera 7

    Basement HVAC Room
    Basidiospores 13
    Ascospores 7

    Myxomycetes 13
    Cladosporium 33
    Basidiospores 27
    Aspergillus / Penicillium 13
    Ascospores 13

    Cladosporium 7
    Basidiospores 33
    Aspergillus / Penicillium 13
    Ascospores 20

    An information you can provide regarding the results is greatly appreciated.

    Warm regards,



    The sample in the basement is slightly concerning, Chaetomium is a water damage indicating mold, and is not present in buildings normally. The result is very low, so it could be a false positive or a very small amount of mold in this area. To me, I would further investigate this area.

    Hi Dylan. Have a multi-level home in Escrow and the home inspector’s mold test came back as follows. Home has radiant in-floor heating, so no HVAC ducting or AC. It is in Utah, snow on the ground, low humidity. There is a crawlspace. Spoke with a mold guy he recommended this morning and that person read the report and said it was ‘alarming.’ He is going to visit the property today to poke around. Home Inspector did not see any mold visually. No odors. Sample was taken outside and several samples in various indoor rooms as follows. Numbers are spore count followed by m3.

    Alternaria 1/13
    Smuts/Myxomycetes/Periconia/Rusts: 1/13

    SW Lower BR:
    Ascospores: 5/67
    Aspergillus/Penicillium: 147/1960
    Basidiospores: 13/173
    Chaetomium: 5/67
    Cladosporum: 9120
    Curvularia: 1/13
    Smuts/et al: 68/907
    Stachybotrys: 680
    Total: 254/3387

    North Lower Level Bedroom:

    Ascospores: 3/40
    Asperillus/Penicillium: 41/547
    Basidiospores: 3/40
    Chaetomium: 1/13
    Cladosporum: 2/27
    Smuts et al: 25/333
    Stachybotrys: 5/67
    Total: 80/1067

    Lower Level Family Room

    Ascospores: 7/93
    Aspergillus/Penicillium: 189/7530
    Basidiospores: 5/67
    Chaetomium: 8/107
    Cladosporum: 25/333
    Smuts et al: 61/813
    Stachybotrys: 4/53
    Total: 299/3987

    Laundry Room (mid level)

    Ascospores: 1/13
    Aspergillus/Penicillium: 22/293
    Basidiospores: 2/27
    Cladosporium: 4/53
    Smuts et al: 9/120
    Stachybotrys: 2/27
    Total: 40/533

    Master Bedroom (top level of home)

    Basidiospores: 1/13
    Cladosporum: 4/53
    Smuts et al: 8/107
    Stachybotris: 1/13
    Total: 14/187

    Would this be considered ‘alarming’ in your opinion? Hoping to keep this deal together but there seems to be so much conflicting info out there.



    I would say these levels are concerning. There are high levels of Aspergillus/Penicillium indoors, combined with water damage indicators such as Chaetomium and Stachybotrys in the samples. These results tell me there is either ongoing or past severe moisture issues in the property.

    Hi! We are currently selling our 6 year old home home in an area that has had several new homes with moisture and mold issues. A potential buyer had air quality testing done, which showed:
    Aspergillus penicillin raw count 17 (370/m3)
    Chaetomium raw count 1 (20/m3)
    Outdoor control showed 0 aspergillus & chaetomium.
    Buyer pulled their offer based on the presence of chaetomium. Home inspection by mold inspection company was unable to locate any areas of concern via thermal imaging and moisture readings of drywall and baseboards in finished basement.
    Should we be concerned? We are unsure of how to proceed.


    These levels are very low, and to me would not be setting off major alarms. A single spore of Chaetomium could, however unlikely, enter the home from the outdoors. Another possibility is it could have been on the mold inspector’s clothes or equipment before they entered your home. If an experienced inspector did not find any mold or moisture concerns in your home, it is likely that the Chaetomium was just an anomaly, not an indication of mold growth in the home.

    Hi we recently had an air sample test taken in our home after finding mold in our upstairs bathroom subflooring. Which we had removed/ replaced with new subflooring. The test was done 2 days after it was replaced. The question now is do we need to Fogg to kill off the ramaing mold spores in the air? It seems like a low level to me are these numbers of any concern?

    Sample 1. — Indoor (2nd Floor)
    Pen/Asp group — 267 Spores/cu. mHyphal Fragment — 53 Spores/cu. mAscospores — 53 Spores/cu. m

    Sample 2. — Outdoor
    No Fungal Spores Observed — N/A Spores/cu. m Dust / Debris: Very LowOpaque Particles: Very Low

    Fogging is not a recommended step in any remediation project. You need to physically remove mold from the air, not just kill it. These levels are within the expected background levels, and wouldn’t require any additional measures. If you wanted to, you could have an air scrubber run in the space for a day or two, but I would not recommend fogging.

    Hi, I am wondering if these lab results are concerning? Its difficult to tell from the report and a little frustrating. Thank you for your help!

    Raw Count Spores
    Basidiospores 18 960
    Cladosporium 8 427
    Pen/Asp group 8 427
    Ascospores 1 53
    Bispora 1 53
    Mitospores 1 53
    Smuts/Periconia/Myxomycetes 1 53
    Hyphal Fragment 3 160


    To effectively interpret lab results there needs to be an outdoor control sample collected at the time of the indoor samples. Without that reference sample, I can not reliably interpret lab results. I can say there are no major red flags on this sample, but there could be minor issues. Again, the finer details can not be interpreted without that outdoor sample.

    Had water leak and thus in 2 bedrooms had “scores” of 2,200 spores/m3 and 1,300 spores/m3 re Chaetomium. Had mold remediation work done (replaced floors/ripped out sheetrock etc) now scores of 120 spores/m3 and 430 spores/m3-do I still need to do further work here or at ok levels. Outside reading basically zero.
    Also at same time first test done living area was ok now on second test had score of 1200 spores/ms outside reading 400 for Penicillium/aspergillus-is this an issue now and not sure how living area only had score of 170 before around a month earlier (note could dust cause this as house not lived in a lot over last month)


    I would suggest having the remediation company perform additional air scrubbing and do a detailed cleaning of the area using a HEPA vacuum. These numbers seem like they are just residual spores in the air from the remediation that needs to be cleaned. Ideally, the Chaetomium levels should be zero indoors.


    I’m looking at purchasing a newly renovated home and have results from outdoor air and 2 indoor samples. I’m particularly looking for some help interpreting hyphal fragments being detected (particularly the Living Room result) – what do these indicate? I am also curious if you see anything else that you’d deem noteworthy and potentially indicative of a problem. Thanks in advance!

    All samples 150L, Air-O-Cell analysis (Methods MICRO-SOP-201, ASTM D7391)

    Outdoor air
    Raw Count / (Count/m^3) / %
    Basidiospores – 5 / 100 / 71.4%
    Cladosporium – 1 / 20 / 14.3%
    Myxomycetes – 1 / 20 / 14.3%
    Total – 7 / 140 / 100%
    Hyphal Fragment – 1 / 7 (found at 300X)

    Living Room
    Aspergillus/Penicillium – 5 / 100 / 14.5%
    Basidiospores – 25 / 510 / 73.9%
    Cladosporium – 4 / 80 / 11.6%
    Total – 34 / 690 / 100%
    Hyphal Fragment – 4 / 80 / — (found at 300X)

    Finished Basement (shares wall with a crawlspace)
    Ascospores – 1 / 20 / 12.5%
    Asperigillus/Penicillium – 2 / 40 / 25%
    Basidiospores – 4 / 80 / 50%
    Cladosporium – 1 / 20 / 12.5
    Total – 8 / 160 / 100%
    Hyphal Fragment – 1 / 7 / — (found at 300X)


    I don’t see any concerns in these results. Hyphal fragments are growth structures for mold. Lab reports note them more as background information, these levels don’t indicate any issues.

    We received our pre-remediation test results back and a handful of mold organisms were found: Alternaria (spore estimate very heavy and mycelial estimate many), Ascospores (27/m3 & 40% of total), Chaetomium (27/m3 and 40% of total), and Cladosporium (13/m3 and 20% of total). The remediation company indicated that he would highly recommend fogging the entire residence since Chaetomium is mycotoxin-producing and that filtration media cannot clean the air because the particles are too small.

    In my minimal research online I’ve read concerning things about like “people who are exposed to Chaetomium may be predisposed to permanent neurological damage of the myelin sheath” and “can also cause permanent DNA damage” and “Chaetomium is the only mold that inhibits cell replication”. In light of this information, I’m reaching out to you as a second opinion on what we should consider in our next steps. I’d like to approach this from an informed standpoint as i’m concerned not just about the mold, but also the fogging chemicals as i have 2yo and am 8 months pregnant.

    Thanks for your help!

    Fogging is not a proper method for mold remediation. The “Holy Bible” of mold remediation, IICRC S520 does not recommend fogging in any capacity. The mold needs to be physically removed from the environment, not just killed by a chemical. I would find a remediation company that will follow S520 to properly take care of the mold.

    Again, no industry guidelines recommend fogging. Fogging will only kill the mold, but even dead mold poses health concerns, therefore the mold needs to be physically removed from the environment.

    Hello Dylan,

    Thank you for taking a look at samples. I hope you are well.

    I was hoping to buy a house in contingency inspection. But I am not sure what to make of some samples.

    In the living room/dining room, the counts are:

    (Type, Raw, Count/m3)
    Acospores 6/40
    Aspergillus/Penicillium 1/7
    Basidiospores 5/33
    Chaetomium 1/7
    Cladosporium 5/33
    Pithomyces 1/7
    Smut etc. 1/7
    Stachybotrys 1/7
    Total 21/140

    Acospores 42/280
    Aspergillus/Penicillium 4/27
    Basidiospores 26/173
    Cladosporium 23/153
    Smut etc. 1/7
    Total 96/640

    We are confused about the living room findings. All we can think is that there was a lot of houseplants in the house. Could that account for the single spore each of chaetomium and stachybotrys?

    The sunroom and kitchen, which are connected to the living room/dining room, have lower levels of all mold and no signs of stachybotrys and chaetomium. There is clear mold contamination elsewhere, though. In the attic, there is spot with 3,202,800 count/cm3 of cladosporium found via tape (no other mold detected, but could stachybotrys be there but just crowded out by the cladosporium?).

    In the walkout basement, there is a crawl space with contaminated unfinished drywall, the tape sample for which revealed aspergillus/penicillium of 13,860 count/cm3 and 15 ascospores and 15 smut etc., but again no stachy or chaetomium.

    Our other question pertains to the finished walkout basement spaces. These are all higher.

    Basement back bedroom:

    Alternaria 1/7
    Aspergillus/Penicillium 163/1087
    Basidiospores 3/20
    Cladosporium 4/27
    Curvularia 1/7
    Smut etc. 2/13
    Total 174/1,160

    Basement front bedroom
    Alternaria 1/7
    Ascospores 2/13
    Aspergillus/Penicillium 419/2,793
    Basidiospores 7/47
    Cladosporium 4/27
    Nigrospora 1/7
    Smut etc. 3/20
    Total 437/2,913

    Basement bathroom (between two bedrooms):

    Acospores 1/6
    Aspergillus/Penicillium 160/1,067
    Basidiospores 2/13
    Cladosporium 4/27
    Smut 1/7
    Total 168/1,120

    Basically, the counts don’t seem terribly high except in the one bedroom. But the outside aspergillus/penicillium count was only 173 count/m3 and everywhere in the basement it is higher. Even the basement family room, which had – total spore count of 687 count/m3, had aspergillus/penicillium finding of 573 count/m3.

    What we know of the basement is most of the carpet (and drywall) is original to the 1989 construction. The basement bedroom with the highest count had a leak onto the carpet until they “fixed” the grading (it is or has become flat, though). The mold inspector told us she thought hiring a remediation company to remove the carpet (and sand and remove the mold on the attic sheathing and remove the crawlspace drywall) would do the trick.

    But this all seems like guessing. We are concerned we will end up having to tear out all the drywall and rebuild, which seems complex, because three sides of these rooms have concrete wall four feet up, until the walls clear the soil, at which point studs sit on the concrete to complete the wall system. This seems fraught from a condensation standpoint, to have wood on concrete, and I don’t know what would have been done in Minnesota in 1989, whether bare wood would have been affixed to bare concrete.

    I am very allergic to mold. We would have to be able to effectively remove it all. Do you see the potential for great expense here? A need to remove not only carpet, but walls?

    Thank you for any insight!


    You really won’t know the extent of things until you look. The Asp/Pen levels throughout the basement are elevated, it could be the carpet but it also could be something else we just can’t know at this point. I would start with removing the carpet and padding, and maybe have some exploratory holes cut into the drywall in a few places to check for hidden mold growth.

    These levels are not off the charts, total remediation is possible but I have seen projects similar to this go both ways. It could be as simple as removing the carpets and doing some air scrubbing, but there could also be more pervasive issues you don’t know about yet.

    The Chaetomium/Stachybotrys in the dining room could be from the plant soil, if there is no moisture or past water damage in these areas I would lean more towards it just being an anomaly. It is more possible these types could be found on the crawlspace drywall than in the attic, a tape sample is only about a square inch of area, and if the Chaetomium/Stachy was growing in an area of the affected wall that was not sampled, we would miss it.

    Hi Dylan. I have a three-season-room that is entirely made of wood – no insulation or sheetrock. It was an old deck they enclosed. The air sample was declared ELEVATED with Penicillium/Aspergillus identified as disproportionally higher when compared to the control sample. The control identified No Spores/m³ while the air sample of the Back Sun Room area noted 920 Spores/m³. I spent a lot of money on this report and wanted to discuss abatement with an honest non-bias expert such as yourself. Would the fact that one of the windows in that room has been not quite sealed up and the house being empty for a year make a difference? Also we are about a block from the Long Island Sound which is about 25% salt water (I think) and across the street from a large pond. Just wondering what you think we need to do and how bad this actually is. Our inspector seems like someone who just does this on the side so not super helpful. Thank you!!!

    Those results are slightly elevated, and unless you are seeing visable mold growth or water intrusion there probably isn’t a need for remediation. Just do a detailed cleaning of the room and the numbers should go to a more normal level.

    I know you’ve mentioned foggers aren’t recommended for remediation but after cleaning should we maybe do that for thoroughness?

    If the cleaning is done properly there is no need for fogging. No industry standard uses fogging as a step in remediation, so I would not recommend it for any reason in a mold project.

    You should read the EPA’s guide on mold remediation in schools and large buildings as well as IICRC S520. These topics are getting away from the purpose of the blog post, I wish you well in your cleaning/remediation efforts!

    Can you help us understand this? Daughter with 10 months moving in she has been diagnosed with asthma. Have all the counts and comparisons.

    Hello, I would just like to know if my ERMI test results should be concerning or if investing in an air purifier would do the job. A little background info: I live in a very small 300 sq ft. apartment and have had worsening symptoms of fatigue, digestive issues, and headaches (thus the doctor’s recommendation to get this done). On top of this, mold exposure actually showed up pretty high on my blood test. I’ve been suspicious of my AC/Heating unit since moving in. It’s a big unit–over a meter long and projects about a foot inside under the window. It smells horrible and the fans inside are caked with what looks like mud, but I’m pretty sure is years worth of mold/mildew buildup. Judging from the ERMI results, is it plausible that this could be from the AC unit alone? I have no visible mold anywhere else.
    Aspergillus penicillioides – 1300
    Aspergillus versicolor – 180
    Cladosporium sphaerospermum – 100
    Eurotium (asp. Amstelodami – 2000
    Stachybotrys chartarum – 1
    Wallemia sebi – 46
    Ccladosporium cladosporioides 1 – 290
    Cladosorium cladosporioides 2 – 20

    Everything else not included above was below 40.


    This blog is meant for help with laboratory air sample analysis, not ERMI. ERMI is very tricky to interpret and is not the ideal way to assess for ongoing mold issues. ERMI looks at dust, which means it is looking into a historical perspective of the home, and can not be used to say if the home has current mold issues reliably. The EPA (who developed the ERMI test) has not cleared the ERMI test to be used in this way.