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More on the Interpretation of Mold Air Samples

Are you staring at the results of a mold test 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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493 thoughts on “More on the Interpretation of Mold Air Samples

    In the process of purchasing a home I found out there was water damage on the first level ceiling/ second level floor. I had my inspector do a mold test and these are the results..

    Outdoors- raw/m3/%of total

    Alternaria (Ulocladium) 2/10/.2
    Ascospores 70/1500/23.1
    Aspergillus/Penicillium 1/20/.3
    Basidiospores 204/4510/69.6
    Cladosporium 18/400/6.2
    Unidentifiable Spores 1/20/.3
    Total Fungi 297/6480/100

    Living room-

    Alternaria (Ulocladium) 1/20/2.4
    Ascospores 1/20/2.4
    Aspergillus/Penicillium 27/600/72.3
    Basidiospores 4/90/10.8
    Cladosporium 5/100/12
    Total Fungi are 38/830/100

    Are any of these results concerning? The report says as/pen is elevated, should I be concerned?

    Asp/Pen would be considered slightly elevated. If you are seeing visable water damage that is a positive indication that there may be some hidden mold growth in those areas.

    Hi Dylan,

    Got the results below from samples in garage. There is a crawl space connected to garage that we can feel is damp / moist when we open the crawl space door. Looks there is a small puddle of water in there as well (probably from the soil from recent rains). Thoughts? Thanks!!!

    Aspergillus/Penicillium 27 raw 9% 360 spores/m3
    Basidiospores 66 raw 21% 880 spores/m3
    Chaetomium 1 raw 0% 13 spores/m3
    Cladosporium 159 raw 51% 2100 spores/m3
    Unidentified Conidia 2 raw 1% 27 spores/m3

    Garage SE Corner:
    Aspergillus/Penicillium 198 raw 61% 2600 spores/m3
    Basidiospores 48 raw 15% 640 spores/m3
    Chaetomium 0 raw 0% 0 spores/m3
    Cladosporium 69 raw 21% 920 spores/m3
    Unidentified Conidia 2 raw 1% 27 spores/m3

    Garage N Side at Crawlspace:
    Aspergillus/Penicillium 153 raw 40% 2000 spores/m3
    Basidiospores 60 raw 16% 800 spores/m3
    Chaetomium 1 raw 0% 13 spores/m3
    Cladosporium 108 raw 29% 1400 spores/m3
    Unidentified Conidia 15 raw 4% 2000 spores/m3

    Total Fungal Spores: 4200, 4300, 5000, respectively

    The Asp/Pen levels in the garage are elevated, however, I should note that air samples in garages are particularly hard to interpret due to how we use garages (storage, parking wet cars, etc), and most garages are not built as tightly as home, so outdoor air infiltrates much easier.

    So after I commented a few days ago about not knowing where to find the outdoor sample comparison results I contacted the company that did the testing. From day 1 the tech seemed to be very short and aggressive with me. Refused to test the areas I outlined as the most problematic and said he could only test the areas the landlord requested as he paid for the test. which the landlord then immediately insisted on testing “random areas” he also refused to test the attic (my biggest concern after vent was damaged in a storm last year and water was just pouring in) and then made him test the opposite end of the basement from where the water damaged in last years flood even though there was visible mold growing. The techs behavior was so off it was almost as if he was a relative or friend of the landlords. So anyways…Come to find out ( grateful to your website or I never would’ve known to ask for outside comparisons ) the tech admitted that he never took a sample of the outside air. First he lied and told me it was raining and the test wouldn’t have shown anything in the air because of the rain. Once I corrected him and told him that’s not the truth because my neighbors home (which was tested the same day) had all of her windows open because it was such a beautiful day. He backtracked and told me that maybe it had rained a few days before that. Then he continued to refer to the levels found in my home as trace amounts which I’m not sure if that is true or not, (the testing wasn’t even done in the right places so I can imagine the results if they had been) and finally he refused to come take an outdoor sample so I have something to compare to. It just all seems so shady. I feel like he is trying to protect the landlord. Can I insist that he come take an outdoor sample? I really don’t know what to do. I’m wondering if I just need to contact board of health and request testing. Any advice you have for me would be greatly appreciated. Thanks again.

    The air sample needs to be taken at the same time as the indoor samples. The air outside your home now will be different than when they took the initial test.

    Help please !
    We we’re smelling a funny “soil” earthy smell in the bonus room. Because of this we got some air quality tests done . It shows we have high amount of Basidiospores found in the bonus room .
    The count was 7860 count /m3 where as outside was 200 and basement was 480.
    We are completely confused. We have had many companies tell us they are stumped as nothing shows water damage , no moisture in the house or attic. And no other Mold spores were found.
    They want to do another air quality test but I’m assuming there is something wrong as the smell is present .
    Please let us know if you have heard of this issue before and if we are safe in the meantime as we research the issue

    Basidiospores typically come from mushrooms. If the bonus room is over a crawlspace, I would check below. Also consider having someone assess the exterior of the home in this area for places moisture could be entering, as the moisture could be affecting only the exterior plywood, and not getting the inner drywall wet so I could go unnoticed by people assessing the interior of the room.

    My question for you is where to find the outside sample results. Is there a specific terminology that I am just not recognizing? It seems I’m other comments people have received a reference point to judge their samples on but my results don’t seem to have any outside info.
    My results from the basement are as follows:
    Aspergillis/penicillium type- 11/ 590
    cladosporium- 9/ 480
    Hyphal fragments- 2/ 110
    Myxomycetes/Smuts/periconia- 1/ 53
    Unknown spores- 1/ 53
    Black opaque particles- 164/ 8700
    Misc. fibers- 14/ 2300

    (My basement is covered in this strange black brown furry type stuff which I assume read as black opaque particles)

    Since putting 2 air purifiers in each room my health has improved slightly but my eyes and lungs are still a mess. but I should add that I have a compromised immune system from cancer and treatments and have been sooo sick and so has my neighbor who has always been perfectly healthy individual. Now her breathing issues are just as bad as mine. Landlord says these numbers are very low and we should be fine but since reading your page I have realized that I don’t think we have been given the full report because there is no mention of an outdoor count.

    Thank you in advance. Any help you can give is greatly appreciated!! :)


    The outdoor reference is a sample that the inspector collects at the time of the assessment outside of the property. That is the only way to find the outdoor values for your sample.

    HI there I work in an old courthouse and they did a quality air control test in my office which approximately a 12 x 15 ft space. The mold spore results came back 1800 but it didn;t say 1800 what?? Is this a normal level or harmful?? Other areas tested were 500, in another office, 700 in attic and 500 in another office. Thanks in advance


    There is nothing I can say with this level of detail. I would need to know the levels and types of individual mold that was found, as well as an outdoor reference sample to compare.

    Hi, so in my room they did an air test [been having a lot of health issues, including hocking up blood]

    [Inside Masterbedroom]
    Raw count: 18
    Count /m3: 240
    % of total: 90.0%

    Raw Count: 4
    Count /m3: 53
    % of total: 3.9%

    Is this serious? Do I need to throw everything away if I move?

    240 spores/m3 is not a high level of Asp/Pen. We can see this type at 1000 spores/m3 routinely in the outdoor air, so 240 is not high.

    I can not say if you need to discard item, as this is testing the air, not the surface of materials.

    Thank you for this helpful site. I have had an air sample done on a home we are under contract with. I had done a dust sample and it looked good downstairs but when we did the air samples on up and down.
    aspergillis /pen Outside= 1 spore/ M3 27 ; upstairs 5 spore/ 67 M3 ; downstairs 10 spore /133 m3

    Cladosporium outside= 18 spores /m3 120 ; upstairs 26 spores / 347m3 downstairs 17 spores / 227 m3

    Chaetonium upstairs 2 spores / 27 m3

    We have dust tested so many homes and it seems impossoble to find a place with really low counts. What are your thoughts?
    There is a bathroom and carpet upstairs.

    THe only thing that sticks out on these results is the Chaetomium in the upstairs samples. The other types found are all slightly higher than outdoors, but well within acceptable levels of what would be expected.

    We just got our mold test results. The mold counts are in cm2 instead of m3. What is the difference? We got cladosporium counts of 61,771 cm2, 155,570 cm2, and 187,600 cm2. Does this require professional remediation?

    I am not sure what those units are referring to, for air sampling industry standard is to report in spores/m3, cm2 makes me think the samples might be surface samples, however 187,000 cm2 is a huge surface area so I am doubtful they are surface counts. You should contact the person who performed the analysis for further clarification of the units.


    How would you assess the following and what would be your recommended course of action, if any:

    Location: Raw Spores / per m3

    Outside: 2 / 90
    Kitchen: 1 / 40
    Closet: 10 / 440

    Outside: 60 / 2700
    Kitchen: 18 / 800
    Closet: 3 / 100

    Thank you so much!


    The only thing slightly concerning is the Asp/Pen in the closet. I am not sure if this is a small closet, or large walk in closet, but the level is higher than the control samples. However, the levels are still below what we can experience in the outdoor air at times. I would make sure there are no moisture problems in the closet, and give it and the contents in the closet a good cleaning outdoors. If there is no moisture or visable mold that is likely all you will need to do.

    Hi Dylan,

    We recently received the following readings from a mold test of a powder room wall cavity in Los Angeles – are these within normal ranges or elaveted?

    The results were classed as “slightly positive”

    Total Spore Count
    Chaetomium 33
    Cladosporium 100
    Penicillium/Aspergillus types 270


    The presence of Chaetomium is raising a red flag to me. While the total level of mold in the sample isn’t alarming, Chaetomium is a water damage indicator mold. I would recommend having someone cut into the wall to have a more visual check in the cavity for mold and moisture problems.

    Hi Dylan,

    A recent mold test was done in my home and remediation was recommended for my living room. Rust was found along the carpet tack. All samples were below outdoor levels except the following;

    (Raw, /m3)
    Indoor – 1, 10
    Outdoor – none

    (Raw, /m3)
    Indoor – 2, 20
    Outside – none

    Would you recommend remediation for these levels?

    Those levels are pretty low, however, Chaetomium and Stachybotrys are water damage indicator types. Knowing that, and you mentioning that there was rust on the tack strips under the carpet does tell me there have been some water issues in the home. If you do not see any visual mold I would recommend performing a detailed cleaning of the area and be very diligent in looking for moisture after precipitation.

    Hi Dylan, I just got my air quality test back and here are the results. We are looking to purchase a home and very concerned. Is this a deal breaker at 17,000 pen/asp. Unfortunately the home inspector who does air quality is not able to give us any more information rather than call a mold expert. Can something at 17,000 level be rectified?


    Spore Trap Samples – Spores per Cubic Meter

    Main Floor
    Pen/Asp group
    Hyphal Fragment

    Basement #3
    Pen/Asp group
    Hyphal Fragment

    Basement #1
    Pen/Asp group

    Basement #2
    Pen/Asp group
    Hyphal Fragment



    I agree, the Pen/Asp levels are high. Also I would add another red flag in the levels of Stachybotrys found in the main floor sample.

    Hello. We had a mold inspection in a master bathroom. In the air test they found the following:
    Chaetomium. Raw count 7. with 373 spores/cubic meter

    Pen/asp:. Raw count 4 with 213 spores/cubic meter

    Cladosporium: raw count 2 with 107 spores/ cubic meter

    Basidiispores: 1 with 53 spores/ cubic meter

    Hyphal fragment: raw count 2 with 107 spores/ cubic meter

    In addition we had a tape test behind the tub surround. Chaetomium, basidiispores, pen/asp group, and stachybotrs we’re all found listing less than 5 percent of the sample area except for chaetomium with was 5-25 percent.

    Recommended for a $2000 rip out with filtration and such.

    Does this seem appropriate?


    I can not comment on the price of remediation or the scope, but the presence of mold on the surface sample and in the air sample indicate there is physical mold growth in the area that should be removed. The EPA states mold growth under 10 square feet can be addressed by the homeowner, so if the area is small it is something you could likely perform yourself. I would look up the free EPA guide on mold remediation in schools and large buildings as a resource.


    The indoor levels in the basement and main floor are elevated, but the level is not outside of the range of what you could expect see in an outdoor sample in the spring and summer months in most of the US.

    Dylan, Thank you for any help you can offer. I moved into a 2cd floor unit in a multi unit dwelling and have become asthmatic and short of breath with other health issues.
    Air Sampling was done and these are the results. Can you tell me what these results mean?
    Outdoor – raw count – 2
    count/m3 -27
    % of total – 67.5%
    Living Room – raw count -1
    count/m3 -13
    % of total – 32.5%
    Bedroom – raw count-2
    count/m3 – 27
    % of total -50.9%
    Outdoor -raw count -1
    count/m3 -13
    % of total – 32.5
    Living Rm – zero
    Bedroom – zero
    Outdoor – 0
    Living Rm -raw count – 2
    count/m3 -27
    % of total – 67.5%
    raw count – 1
    count/m3 – 13
    % of total – 24.5%
    Outdoor – zero
    Living Rm – zero
    raw count -1
    count/m3 -13
    % of total – 24.5%

    The only suspect thing on these results is the small amount of Chaetomium found in the indoor samples. These results are low, but Chaetomium is a water damage indicating mold type which may suggest there have been some past or ongoing moisture problems in the unit.

    ST1: Kitchen
    Lower Higher
    <110 200 300
    Mold Score 188

    Lower Higher
    spores/m3 spores/m3
    Location 3,262
    Outside 6,400

    ST2: Bedroom
    Lower Higher
    <110 200 300
    Mold Score 300

    Lower Higher
    spores/m3 spores/m3
    Location 13,833
    Outside 6,400

    ST3: Laundry Room
    Lower Higher
    <110 200 300
    Mold Score 246

    Lower Higher
    spores/m3 spores/m3
    Location ,3466
    Outside 6,400

    Surface Sample Summary:
    The surface sample results of DE1, DE2 indicated mold growth on the surface(s) sampled at the time of sampling.

    Location Mold Growth Dominant Types
    DE1: Bedroom – HVAC
    Mold Growth- Cladosporium species
    DE2: Laundry Room – Base board
    Mold Growth -Chaetomium species

    Air sample:
    ST2: Bedroom
    Overall Mold Source Assessment*
    (Likelihood spores originated inside)
    Lower Higher
    <110 200 300
    Mold Score

    Overall Exposure Level
    Lower Higher
    spores/m3 spores/m3
    Location 13,833 Outside 6,400

    Indicators of Mold Growth
    Indoors Indicator Mold Source Assessment*
    (Likelihood spores originated inside)
    Lower Higher
    <110 200 300

    Indicator Exposure Level
    Lower Higher
    spores/m3 spores/m3
    Location 5,200

    A) Penicillium/Aspergillus types** Exposure 300 Location 5,200 Outside 210
    B) Cladosporium species spores Exposure 260 Location 8,200 Outside 5,000
    C) Basidiospores Exposure 100 Location110 Outside 590
    “Other” spore types***,**** Exposure: 143 location 270 outside 316
    “Others” with MoldSCORE™ > 100 (maximum of five listed): 1)Smuts, Periconia, Myxomycetes
    Other Sample Information Other “normal trapping” spores

    ST3: Laundry Room

    Overall Mold Source Assessment*
    (Likelihood spores originated inside)
    Lower Higher
    <110 200 300
    Mold Score

    Overall Exposure Level
    (Shown on a log scale)
    Lower Higher
    spores/m3 spores/m3
    Location 3,466 Outside 6,400

    A) Penicillium/Aspergillus types**
    Indicators of Mold Growth
    Indoors Indicator Mold Source Assessment*
    (Likelihood spores originated inside)
    Lower Higher
    <110 200 300
    Mold Score
    Exposure Level
    Lower Higher
    spores/m3 spores/m3
    Location 850 Outside 210

    B) Cladosporium species spores mold source assessment 100 Location 2,400 Outside 5,000

    C) Basidiospores mold source assessment 100 Location 53 Outside590

    “Marker” spore types*** 246 110 100 (maximum of three listed): 1)Chaetomium

    “Other” spore types***,**** 121 53 316
    “Others” with MoldSCORE™ > 100 (maximum of five listed): 1)Bipolaris/Drechslera group

    MoldREPORT: Direct Microscopic Examination
    Location: DE1: Bedroom – HVAC DE2: Laundry Room – Base Board
    Comments (see below): None None
    Lab ID-Version‡: 10024766-1 10024767-1
    Spore types present (indicative
    of mold growth)§:
    Aureobasidium – –
    Basidiospores – –
    Chaetomium – 3+
    Cladosporium 3+ –
    Fusarium – –
    Lumber mold† – –
    Penicillium/Aspergillus types – –
    Stachybotrys – –
    Trichoderma – –
    Ulocladium – –
    Spore types present (not
    indicative of mold growth)§:
    All spore types – Very few
    Other particles detected§:
    Skin cells Very few Very few
    Pollen – –
    Background Debris and/or
    Scant Light

    MoldREPORT: Spore Trap Analysis
    ‡ A “Version” indicated by -“x” after the Lab ID# with a value greater than 1 indicates a sample with amended data. The revision number is reflected by the
    value of “x”.
    † Background debris is an indication of the amounts of non-biological particulate matter present on the slide (dust in the air) and is graded from 1 to 4 with 4
    indicating the largest amounts.
    The analytical sensitivity is the spores/m^3 divided by the raw count, expressed in spores/m^3. The limit of detection is the analytical sensitivity (in spores/m^3)
    multiplied by the sample volume (in liters) divided by 1000 liters.
    § Total has been rounded to two significant figures to reflect analytical precision.
    Location: ST2:
    Laundry Room
    Comments (see below) None None
    Lab ID-Version‡: 10024770-1 10024771-1
    Analysis Date: 03/18/2019 03/18/2019
    Spore types detected: raw ct. per m3 raw ct. per m3
    Aureobasidium – – – –
    Basidiospores 2 110 1 53
    Chaetomium – – 8 110
    Cladosporium 153 8,200 45 2,400
    Fusarium – – – –
    Penicillium/Aspergillus types 98 5,200 16 850
    Stachybotrys – – – –
    Trichoderma – – – –
    Ulocladium – – – –
    Others 6 320 1 53
    § Total: 14,000 3,500
    Additional Information:
    Hyphal fragments 370 370
    Skin cells 4,000 – 8,000 4,000 – 8,000
    Pollen 110 < 13
    Background debris (1-4)† 4 3
    Limit of detection 13 13

    MoldREPORT: Spore Trap Analysis
    Location: OS:
    Comments (see below) None None
    Lab ID-Version‡: 10024768-1 10024769-1
    Analysis Date: 03/18/2019 03/18/2019
    Spore types detected: raw ct. per m3 raw ct. per m3
    Aureobasidium – – – –
    Raw ct per m3 Raw ct Per m3
    Basidiospores 11 590 1 53
    Chaetomium – – – –
    Cladosporium. 94 5,000 42 2,200
    Fusarium – – – –
    -Penicillium/ 4 210 13 690
    Aspergillus types
    Stachybotrys – – – –
    Trichoderma – – – –
    Ulocladium – – – –
    Others 11 590 6 320
    § Total: 6,400 3,300
    Additional Information:
    Hyphal fragments – 320
    Skin cells. 13-67 4,000 – 8,000
    Pollen 110 < 13
    Background debris (1-4)† 3 4
    Limit of detection 13 13

    Unfortunately, with how the data is posted, I cannot effectively get the data needed for any interpretation. Consider uploading the files and commenting with a link so I can see the reports in whole.

    Hi, We are in the process of buying a home. I have 2 children. My son and I both have asthma. We opted to have a mold inspection. Attached are the results. Just concerned about some of the levels, mostly Pen/asp group. Unsure if the recommendation is enough to take care of the problem and how bad the problem is.
    D uring my inspection of the property, I noted the following:
    • Evidence of surface mold growth on the overhead sub-floor and band-board in the front/left corner of the basement.
    • Evidence of water/mold damage to the wooden legs of the workbench on the left/rear corner of the basement.
    o The water mold damage appears to be a direct result of the downspout on the left/rear corner.
    The IMS Laboratory report (attached) indicates elevated levels of the PEN/ASP group in the basement (4,590 spores/cu.m v. 0 spores/ 0 spores/ cu.m
    Although the levels are elevated, they are still in the low range and consistent with the areas identified in my inspection.
    As previously discussed, the affected areas can be treated by the perspective buyer with an EPA Registered Disinfectant, Cleaner and Fungicide such as Concrobium, Mold Control or Mold Armor (available at Home Depot). Please let me know your opinion of these results. Thank you, Kerrin


    The Asp/Pen results do seem elevated, but without a comparison sample from the outdoor air I can not provide any more detailed interpretation of those numbers.

    Following a medical doctor’s recommendation testing for mold was done using cloth wiping kits. Wondering if the results have any real meaning since all I’m now reading refers to testing the air itself (which does seem more logical) and having a baseline outdoor test to match. Used the wipes to gather aggregated samples from tops of window frames, door frames, tops of bookcases, etc until the cloth was visibly dusty. Lab returned results on 5 types and then calculates a HERTSMI-2 score which came in above the threshold for concern. The lab’s website has little background info and references only the owners(?) publications for further reading. Several rooms tested, with highest results of:

    Aspergillus penicillioides 3500
    Aspergillus versicolor 140
    Chaetomium globosum 11
    Stachybotrys chartarum 2
    Wallemia sebi 3300
    as measured in Spore equivalents/mg

    Does this show anything of use or should we redo the tests with more typical air testing? Sadly a 1000 miles or so too far from you but appreciate any insights!


    Unfortunately, the HERTSMI-2 test does not have any actual information that we can interpret for you. The test is not a useful evaluation of the potential mold exposure in the home.

    We are renting an apartment and had concerns so we hired a company to do a mold test.
    We got our test results back and the company never really explained the results only tried to sell us an equipment package.
    Could you let me know if we need to be concerned with the following readings:
    Raw Count Count/m³ % of Total
    Aspergillus/Penicillium 11 240 32.1
    Basidiospores 16 350 46.9
    Cladosporium 3 70 9.4
    Please advise and thank you

    Just got a test back ! Test suggested remediation in bedroom wall cavities under bedroom windows !

    Test came back:

    Outside air sample:
    Ascospores count/m3 = 40
    Basidiospores count/m3= 67
    myxomycetes count/m3= 13

    Air sample from bedroom tested:
    Aspergillus/penicillin count m3= 173
    Ascospores count/m3= 27
    Stachybotrys count/m3= 13

    Air sample from wall cavity in bedroom under window #1:
    Altermaria count:m3=67
    Ascospores count/m3= 267
    Aspergillus/penicillium count/m3=333
    Curvularia count/m3= 67
    Myxomycetes count/m3= 267

    Air sample from wall cavity in bedroom under window #2:
    Aspergillus/penicillium count/m3=333
    Basidiospores count/m3=200
    Cladosporium count/m3= 200

    Hoping I wrote these in right and thank you so much for your time !!!!

    The samples from the wall cavities seem normal, and based on just those samples I do not think remediation is needed. However, Stachybotrys was found in the bedroom sample, and that may indicate past moisture and hidden mold growth which I would want to look further into.

    Hi Dylan,

    I am looking at purchasing a house and had a mold air test done in the basement. It found:
    Chaetomium 10,385 / m3
    Penicillium/Aspergillus 1,206 / m3

    Neither of these were found in the outdoor sample.

    Of course the person who took the sample wasn’t really able to explain much to me and recommended fogging the basement and scrubbing the air with HEPA filters. So I’ve been trying to do some research myself and evaluate the risk level. I’ve read that Chaetomium spores in air are typically found after the fungus has dried out when spores are more easily dispersed. Chaetomium also seems to indicate a relatively serious moisture issue had occurred at some point.

    We did find a water valve that was leaking onto some wood trim on the floor and wetting approximately 3 feet of trim. Could that have caused numbers that high? I was kind of poking around the trim a bit about an hour before he did the test so I wonder if I disturbed the spores and elevated the numbers for the test.

    Do these numbers suggest a significant water issue has occurred at some point?
    Would a fogging and HEPA filter treatment make sense?
    Are Chaetomium numbers this high worthy of big concern?

    I appreciate any advice.

    Those Chaetomium levels are very high, I would say there have likely been some significant water issues in the home. Fogging and air scrubbing isn’t likely to fix the issue. You need to have someone do a detailed assessment in the home and find where the physical mold growth is, and have it removed. Air scrubbing is used in combination with physical removal of mold growth, but can not replace it. Fogging for mold is not an accepted method of addressing mold.

    600x MagCounts/Calculated Counts m3/calc %

    Stachybotrys- 3/40m3/60%

    Is this a concern? Thats the indoor reading. No presence of these spores in outside test


    The presence of Stachybotrys in the indoor environment is a red flag for water damage and mold growth. This type is very rare in the naturally occurring outdoor air, so showing up in the indoor air is suspect.

    Hello Dylan! We got our results back for a home during inspection and aren’t sure how to interpret. 1500sqft home built in the 50s:

    • Outside: 320 ct/m³
    • Inside: None

    Other Ascospores:
    • Outside: None
    • Inside: 880 ct/m³

    Other Basidiospores:
    • Outside: 200 ct/m³
    • Inside: 160 ct/m³

    • Outside: 1400 ct/m³
    • Inside: 560 ct/m³

    Thanks for your generosity in helping us all understand these reports. We recently had testing done and the results were:
    raw ct spores/m3 %
    Ascospores 7 280 5
    Basidospores 64 2560 42
    Cladosporium 24 960 16
    Curvularia 1 40 <1
    Pen/Asp 54 2160 35
    Smuts/Periconia/Myxomy 2 80 1
    Stachybotrys 1 40 <1

    What do you make of those results? Thank you!


    It is difficult to interpret results without an outdoor reference sample collected at the time of the assessment. It seems like there may be an elevation of Asp/Pen, Cladosporium, and Basidiospores. However, I can not say much more without knowing the outdoor levels at the time of testing.


    We are renting an apartment and had concerns so we hired a company to do a mold test.

    We got our test results back and the company never really explained the results only tried to sell us an equipment package.
    Could you let me know if we need to be concerned with the following readings:
    Raw Count Count/m³ % of Total
    Aspergillus/Penicillium 11 240 32.1
    Basidiospores 16 350 46.9
    Cladosporium 3 70 9.4

    Please advise and thank you

    Hello Dylan:

    Thank you for indicating that you receptive to inquiries about interpreting test results re: molds.

    We live in a 3rd floor condo, in a 4 storey condo building, in Calgary, alberta- normally a dry environment. Water, probably from melting snow on the deck, seeped into our bedroom ceiling from the 4th floor, probably had been going on a while when we reported it to the condo board in January 2018.
    The cause appears to have been errors in building envelope during the original 2004 construction.

    My husband, now 83 years, has had life long breathing issues- asthma in his earlier years, and daily allergies eg to dust, in his later decades.

    In preparation for the remediation plan the board sent a restoration expert to do preliminary testing for molds. The test report identified 7 molds:
    cts/m3 (outdoor coontrol cts/m3
    Ascospores 80 30
    Basidiospores 670 350
    Chaetomium 30 [no reading]
    Cladosporium 450 530
    Aspergilus 350 [no reading]
    Hyphal Fragments 100 100

    How should we interpret these measurements, in light of my husband’s mysterious allergies which affect him most every morning and seem to clear significantly if he goes out for urban walking etc.?

    Many thanks,
    Best regards,
    Claire McMordie


    The presence of Chaetomium is a red flag that there have been some moisture issues in the property. The other levels all look normal besides the Chaetomium.

    Hi Dylan,

    I recently used a home kit (small vacuum pump and cartridges) and mailing to a lab to analyze two bedrooms and an unfinished attic in my home, and am unclear what action (if any) is indicated from the results.

    The only result flagged as “slightly elevated” by the lab was the “Myxomycete-Like” result in the attic. The report flagged the rest as “normal”. The lab did not specify whether this warranted action, or what action might be needed.

    For background, this sample was taken on a cold day with snow on the ground and very low humidity, but in a season that has had many rapid 30-40 degree weather fluctuations day to day and an immense amount of rain, so I’m not sure I can count on that outdoor measurement. We live in a wooded area in Maryland, and typically have very hot, very humid summers.

    About five years ago, we had our roof replaced due to a leak that led to a water spot in our ceiling, and had some minor ice damming issues 3 years ago. Both leaks were above the vaulted ceiling in the Master Bedroom. There has been no evident water issues since, and I’ve never seen any visible mold.

    Test locations were outside back deck, master bedroom where leaks/damming occurred in past at back of house, daughter’s bedroom in front of hourse, and the small portion of our attic that isn’t vaulted (above master bedroom closet).

    Is there anything of concern here, or actions I should take?

    Thank you for your time!

    Outside Penicillium/Aspergillus 2 100per m^3 100%
    Daughter’s Bedroom
    Cladosporium Species 1 20per m^3 100%
    Master Bedroom
    Basidiospores 2 100per m^3 22.2%
    Cladosporium Species 1 50per m^3 11.1%
    Penicillium/Aspergillus 6 300per m^3 66.7%
    Unfinished attic space
    Basidiospores 2 100per m^3 7.1%
    Blakeslea/Choanephora 1 50per m^3 3.5%
    Cladosporium Species 4 200per m^3 14.2%
    Epicoccum Species 1 20per m^3 1.4%
    Hyphal Elements 1 50per m^3 0%
    Monodictys 1 50per m^3 3.5%
    Myxomycete-Like 14 690per m^3 48.9% <— flagged by analysis lab as "Slightly Elevated"
    Penicillium/Aspergillus 7 300per m^3 21.3%


    Air samples in unfinished attics really shouldn’t be taken. The space accumulates dust and debris, mainly from the outdoor air. So when people inspect and sample in attics we almost always get confusing results. I would have any concerns about the myxomycetes level in the attic sample.

    I have had a test done but have no idea what it means and the company is only telling me to buy this or that!

    Spore Types Raw Count Count/m³ % of Total Raw Count Count/m³ % of Total
    Alternaria (Ulocladium) – 1 20 2.7
    – –
    Ascospores 3 70 1.3
    Aspergillus/Penicillium 46 1000 18.9 11 240 32.1
    Basidiospores 162 3580 67.5 16 350 46.9
    Bipolaris++ – – – – – –
    Chaetomium – – – – – –
    Cladosporium 8 200 3.8 3 70 9.4
    Curvularia – – – 1 20 2.7
    Epicoccum – – – – – –
    Fusarium – – – – – –
    Ganoderma 1 20 0.4 – – –
    Myxomycetes++ 7* 50* 0.9 1 20 2.7
    Pithomyces++ 1* 7* 0.1 – – –
    Rust 1* 7* 0.1 1* 7* 0.9
    Scopulariopsis/Microascus – – – – – –
    Stachybotrys/Memnoniella – – – – – –
    Unidentifiable Spores 2 40 0.8 1 20 2.7
    Zygomycetes – – – – – –
    Botrytis 1* 7* 0.1 – – –
    Cercospora++ 1* 7* 0.1 – – –
    Paecilomyces-like 13 290 5.5 – – –
    Pestalotia/Pestalotiopsis 1 20 0.4 – – –
    Torula-like 1* 7* 0.1 – – –
    Total Fungi 248 5305 100 35 747 100
    Hyphal Fragment 3 70 – 1 20 –
    Insect Fragment – – – – – –
    Pollen 4* 30* – – – –
    Analyt. Sensitivity 600x – 22 – – 22 –
    Analyt. Sensitivity 300x – 7* – – 7* –
    Skin Fragments (1-4) – 1 – – 2 –
    Fibrous Particulate (1-4) – 1 – – 2 –
    Background (1-5) – 1 – – 1 –

    Please help

    buying a place in Utah. Did a Spore Trap Analysis and it discovered the following…
    Ascospores 7/m3, Outside 0/m3

    Smuts/Myxomycetes – 100/m3, outside 40/m3

    In your opinion does this need remediation?


    Appreciate your willingness to share your expertise. Recently we had our home inspected, no visible water damage or high moisture reading in wall sections tested were found, and air samples were taken outside, and in 3 bedrooms along with a surface sample of some mold/staining on a few of the pieces of framing lumber in the attic. We live in central Texas where warm/hot humid weather is the norm. Any red flags in you opinion?

    Alternaria – raw count – 3 spores/m3 – 120
    Ascospores – raw count – 5 spores/m3 – 200
    Basidiospores – raw count – 29 spores/m3 – 1160
    Bipolaris/Drechslera – raw count – 3 spores/m3 – 120
    Cladosporium – raw count – 188 spores/m3 – 7520
    Penicillum/Aspergillus – raw count – 30 spores/m3 – 1200
    Smuts/Periconia/Myxomy – raw count – 2 spores/m3 – 80

    Bedroom 1 – Upper level* Attic was accessed from to different access points in this room prior to test.
    Alternaria – raw count – 1 spores/m3 – 40
    Ascospores – raw count – 6 spores/m3 – 240
    Basidiospores – raw count – 36 spores/m3 – 1440
    Bipolaris/Drechslera – raw count – 0 spores/m3 – 0
    Cladosporium – raw count – 40 spores/m3 – 1600
    Penicillum/Aspergillus – raw count – 44 spores/m3 – 1760
    Smuts/Periconia/Myxomy – raw count – 2 spores/m3 – 80

    Bedroom 2 – Upper level
    Alternaria – raw count – 0 spores/m3 – 0
    Ascospores – raw count – 1 spores/m3 – 40
    Basidiospores – raw count – 33 spores/m3 – 1320
    Bipolaris/Drechslera – raw count – 0 spores/m3 – 0
    Cladosporium – raw count – 16 spores/m3 – 640
    Penicillum/Aspergillus – raw count – 37 spores/m3 – 1480
    Smuts/Periconia/Myxomy – raw count – 0 spores/m3 – 0

    Bedroom 3 – Main level
    Alternaria – raw count – 1 spores/m3 – 40
    Alternaria – raw count – 0 spores/m3 – 0
    Basidiospores – raw count – 21 spores/m3 – 840
    Bipolaris/Drechslera – raw count – 0 spores/m3 – 0
    Cladosporium – raw count – 10 spores/m3 – 400
    Penicillum/Aspergillus – raw count – 20 spores/m3 – 800
    Smuts/Periconia/Myxomy – raw count – 0 spores/m3 – 0

    Surface sample
    Hyphal Fragments – L or 101-1,000 spores
    Cladosporium – VL or 20-100 spores
    Penicillum/Aspergillus – Scattered spores or 1-20 spores.


    The only thing slightly concerning is the Aspergillus/Penicillium levels in bedroom 1 and bedroom 2. They are slightly elevated, but not to the point where I think there is a major issue in these areas. Maybe a good, detailed cleaning of these areas with a hepa vacuum will lower those levels below the background amount.

    The air samples look acceptable, there are some very slight differences from the outdoor sample in regards to the Asp/Pen levels, but it is very slight. The surface sample indicates that the surface does have mold growth, so I would work on figuring out what caused the mold and what needs to be done to fix it.

    I am currently renting an apartment. I’ve been here for about 2 and a half years, and I’ve had several health issues that seem to be getting worse. I never considered mold a possible culprit, but I recently got ground water in my living area, all along the back wall, where the floor meets the plaster, and realized when the water wasn’t getting in, it was sitting somewhere. My landlords agreed to have a mold inspection done, and these were the results of present spores-
    Ascospores – Exterior raw 102 ext cubic meter 4080 31% Interior raw 3 Int cubic meter 120 2%
    Basidiospores – Exterior raw 180 ext cubic meter 7200 55% Interior raw 68 Int cubic meter 2720 48%
    Cladosporium – Exterior raw 10 ext cubic meter 400 3% Interior raw 9 Int cubic meter 360 6%
    Penicillium/Aspergillus – exterior raw 38 ext cubic meter 1520 12% Interior raw 62 Int cubic meter 2480 44%

    There is mildew present on two window panes. No physical sample was taken. There was also no sample taken from the sink or shower in the bathroom (very dark, hard to clean mildew). Additionally, water has gotten into the apartment before, before I moved in, and my landlord’s said it had been taken care of. This is a 350 sq. ft. unit, backing and the back wall is about 2 feet underground. Should I be worried??


    The levels of Penicillium/Aspergillus is elevated indoors. With the history of moisture in the property, I would be interested in seeing what is inside the wall cavity in the area that has been damp. Also, mildew technically does not grow in the indoor environment, what those stains on the windows and shower are is actually mold growth. Some people (especially uneducated landlords) will call growth mildew because they are afraid to say the “mold” word. Mold in the shower is hard to keep a handle on once the discoloration starts since the area is inherently exposed to routine moisture. Growth around windows is an indication of condensation issues in the apartment. This happens when the indoor air is humid and meets a cold surface such as a window in winter.

    The Penicillium/Aspergillus is slightly elevated in the indoor sample. Also, many people will call mold growth mildew in order to downplay it. In fact, true mildews are plant pathogens and do not typically grow indoors. What you are seeing around the window and in the shower is likely some form of mold growth.


    I have a kitchen with Aspergillus/Penicillium-Like spores.
    Kitchen: Raw count at 11 and Count/m3 at 147.
    Outside: Raw count at 6 and Count/m3 at 80.

    Is this considered a low acceptable indoor level for the kitchen?
    Is it 100% safe and if the levels stay at this level, no cause for alarm?

    Additional information:
    Volume Sampled (L): 75
    Media: Air-O-Cell
    Percent of Trace Analyzed: 100% at 600X Magnification

    Thank you for your help!

    Hi Dylan,
    Thank you for helping so many people. Last week I got mold test done in my apartment in New Jersey. Can you please help me understand following results. Do you see anything to worry about?

    The swab result from Bathroom Vanity is Aspergillus Penicillium: Raw count 28; count/cm2 174. Area Swabbed (cm2): 6.45, Analyzed at 600X Magnification

    Following are air sample results; Media: Air-O-Cell, Vol sampled: 150L, Percent of Trace Analyzed: 100% at 600X Magnification.

    Ascospores raw count 18 ; 120 Count / M3
    Basidiospores raw count 13 ; 87 Count / M3.
    Cladosporium raw count 8 ;53 Count / M3
    Curvularia raw count 2 ;13 Count / M3

    Ascospores raw count 1; 7 Count / M3
    Aspergillus Penicillium raw count 65 ; 433 Count / M3.
    Cladosporium raw count 3 ;20 Count / M3
    Ganoderma Raw count 1; 7 Count/M3
    Myxomycetes Raw count 1; 7 Count/M3

    Aspergillus Penicillium raw count 3 ; 20 Count / M3.

    Aspergillus Penicillium raw count 7 ; 47 Count / M3.

    Thank you for your time.


    These results seem to be normal, with a very small amount of ASp/Pen in the bathroom. Both the air sample and swab in the bathroom show only a slight amount of Asp/Pen. I would suggest making sure the bathroom stays dry, use an exhaust fan during and after showers to remove moisture quickly.

    Our family owns a 100 year old building. Our tenant insisted on having a mold test done. The spore trap results showed that the spore counts were elevated compared to the outside.

    Outside baseline spore trap (non-viable methodology):
    Basidiospores: raw ct- 2, spores/m3 110
    Cladosporium: raw ct 41, spores/m3 2,200
    smuts,myxomycetes, periconea: raw ct. 2 , spores/m3 27

    Bedroom 1:
    Penicillium/asperigillus: raw ct 25, spores/m3 2,800
    Cladosporium: raw ct 51, spores/m3 5,700
    Ascopores: raw ct 1, spores/m3 110
    Basidiospores: raw ct 5, spores/m3 560
    Chaetomium: raw ct 3 spores/m3 40

    Bedroom 2:
    Penicillium/aspergillus: raw ct 21, spores/m3 2,300
    Cladosporium: raw ct 32, spores/m3 3,600
    Ascospores: raw ct 1, spores/m3 110
    Chaematomium: raw ct 5, spores/m3 67

    Report did not show presence of other molds. Humidity readings taken on day of test was 52%. Air sample in bedroom 2 was taken near a closed window that reportedly show surface mold growth.

    We are concerned because the mold investigator wants 5 more air tests around the house to determine if there is wide spread “contamination.” I question the additional testing, because they want air samples taken directly next to the windows which show visible signs mold. These windows/blinds are also caked in dust. My guess is that the results will show elevated levels of spores. Also per EPA and CDC, if there are visible signs of mold, there is no need for more air testing.

    There is also wall to wall carpet in the flat which has been in the unit since the tenant moved in 25 years ago. Carpet shows staining and dirt. Also, tenant has had a large dog in the unit for at least 9 years. In the past, there have also been some minor leaks in the house which were repaired.

    He is recommending that the bedrooms be professionally remediated ( carpets ripped out and windows replaced) and depending on the results of the other tests, my guess is he will want the rest of the house remediated (living rm, dining rm, kitchen). The only visible mold is around the window sills, frames, and glass. He also mentions presence of interior condensation on the windows and frames. These are old single pane windows, and they are recommending that these be replaced with double panes.

    My questions:
    1. Do these levels indicate a need for professional remediation? Is he going overboard with his recommendation?
    2. Do we need additional testing for the rest of the flat/apartment? Should we just assume the rest of the house needs professional remediation?
    3. Could the elevated spore count come from the carpet? (no samples were taken)

    I would prefer not to do additional testing as I know this is going to cost us a lot of money (paying tenants to relocate, cost of new windows, cost of remediation, cost of new carpet, etc.)

    Grateful for any advice you could give us.


    Also, I wanted to add – A mold investigator hired by the tenant also ran a test a few weeks earlier, and the results were completely different. His air test showed

    Outdoor sample:
    Cladosporium- raw ct – 22, spores/m3 800
    Penciliium/Aspergillus- raw ct – 0, spores/m3 0
    Other Badiospores – raw ct – 7 , spores/m3 280

    Bedroom1 :
    Cladosporium – raw ct 0, spores/m3 0
    Penicillium/Aspergillus – raw ct 54, spores/m3 2,200

    Bedroom 2:
    Cladosporium – raw ct – 2, spores/m3 80
    other Badiospores – raw ct – 2, spores/m3 120
    Peniciliums/Aspergillus, – raw ct – 32, spores/m3 1300

    All other molds were negligible or zero. We are not sure why there is such a large discrepancy other that they may have sampled it under different conditions or even locations in the room.

    These results are elevated, and the presence of condensation is concerning If you have condensation on the interior surface of windows, you can also be getting condensation in the wall cavity around the window as well. This can lead to mold growth beyond what you are seeing in the window sill. Instead of taking a bunch of air samples around windows with visible mold growth, I would suggest having some small holes cut into the wall near the windows to check for hidden mold growth.

    If the carpet has been wet from leaks or flooding, it could have mold growth. Carpet also acts as a reservoir for mold. This means as elevated levels of mold float around in the air, they will settle onto surfaces. When the mold settles into carpet it can remain trapped in the carpet for long periods of time if they are not cleaned. Over time large amounts of settled mold can become trapped in the carpet.

    Thank you for your response. We live in the fog belt of California so moisture is a constant problem. Do you feel with these elevated counts that professional remediation is warranted?



    I am not a medical professional, so I can not assess if the numbers are healthy or unhealthy. Without knowing the outdoor levels at the time of the assessment, my interpretation is very limited. It seems like these levels are elevated, but I can not say to what extent they are without the outdoor sample results.

    Desr Dylan,
    Thanks for helping people make sense of these lab reports. Its very kind of you to do so.
    I live in Hawaii. Live in an old small home surrounded by a lot of vegetation. Several years ago we had roof leaks that were repaired. Just this past year we began having some roof leaks into the home again and it took the land lord several months to fix. The indoor ceiling is primarily dry wall over the ceiling rafters with little to no crawl spaces to investigate for mold. Clear and evident water discoloration is visible on the drywall in some places. Mold inspectors came in and read high levels of moisture in the lower corners of the ceiling drywall on many parts of the ceiling of the home.
    After the roof was reshingled the landlord had a mold remediation come in. They didn’t remove any of the drywall, but just fogged the whole house for 24 hours with some “special” mold killing enzyme. After the “fogging” the mold sits ample rest they took reported low mold spore counts. I didn’t trust this would work so inrequested another air test 6 weeks after.
    The following is from that test. I know some of these numbers are high, but how concerned should I be;

    Aspergillus/penicillium sp;
    exterior – 1700 spores/m3. RC 18
    Living room – 27000 spores/m3 RC 277
    Bedroom – 4400 sp/m3 RC 46

    Cladosporium sp.
    Exterior -9300 sp/m3 RC 97
    Living room – 3000 sp/m3 RC 31
    Bedroom – 16000 sp/m3 RC 170

    Hyaline sores, acremonium sp.
    Exterior – NA
    Living room – NA
    Bedroom – 12000 sp/m3

    Myxomycetes/ustilago/periconia sp.
    Exterior – NA
    Living room -190 sp/m3 RC 2
    Bedroom – 96 so/m3 RC 1

    Fusarium sp.
    Exterior – 290 sp/m3 RC 3
    Living room – NA
    Bedroom -480 sp/m3 RC 5

    Exterior – 14000 sp/m3 RC 142
    Living room – 31000 sp/m3 RC 324
    Bedroom – 35000 sp/m3 RC 369


    Moldy and water damaged materials need to be physically removed to be properly remediated. While chemicals and fogging agents may “kill” the mold, it does not remove the mold from the indoor environment. Even dead mold can cause health issues, so the only correct way to treat mold is to physically remove it from the space. As shown in your lab results, the indoor levels are still elevated.

    I am currently staying in a rental that has some obvious mold growth. Some existed when we moved in, some grew rather quickly after storm surge due to Hurricane Michael. There is an amazing amount of demo to be done and my landlord’s insurance company is not in a hurry. Below are our results from our recent mold test. I’m trying to determine whether or not it is safe to stay before and during demo/remediation. Thank you for your help in advance.

    Upstairs Bedroom
    Air Sample
    Asp/Pen Raw 81/ m3 1080
    Chaetonium Raw 1/ m3 13

    Downstairs Bedroom
    Air Sample
    Asp/Pen Raw 61875(est due to high count) / m3 825000
    Chaetonium 0/0
    Stachy Raw 13 / m3 173

    Air Sample
    Asp/Pen Raw 17 / m3 225
    Chaetonium 0/0
    Stachy 0/0

    Asp/Pen Raw 30615 / cm2 189860

    That is not enough information to give any feedback. I would suggest looking through some of the comments to see the kind of information others send over for review.

    Hi Dylan,
    Are levels of pen/asp at 5400 raw ct and 9,700,000 per m3 high and if so what would be your recommendation? I was not provided any outside numbers???
    Also the report says:
    Hyphae fragments 30
    Skin cells 67-330
    Pollen <67
    Background debris 3
    Limit of detection 67
    Sample volume (liters) 15

    I have no idea what any of this means
    Thank you


    That is higher than I have ever seen for Asp/Pen levels. Even without outdoor numbers, I can say those are highly elevated. There are some serious mold issues inside the area the sample was collected from.