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

    Hi There! Thanks so much for the work you’re doing here! We’re looking to purchase a home and just got back the air test results. The seller had disclosed that there was a leak due to damaged flashing around the chimney, but it was completely repaired in the basement and living room (drywall, insulation, flashing, wood beams, siding & outdoor deck). The repairs were done about a month prior to our air test but the home has been closed and unused since – the sellers had a remediation company visit who advised that we should add hepa filters and do a top to bottom cleaning of the home but nothing more. I wonder if these levels are in line with recommendation or if it will need a deeper remediation. The living room area has carpet which im guessing could be contributing to the issue.

    [Raw Count / (Count/m3) / % of Total]
    outdoor sample:
    Aspergillus/Penicillium 12 / 250 / 9.6%
    Cladosporium 24 / 510/ 19.5%
    total: 129 / 2610

    unfinished basement:
    Aspergillus/Penicillium: 14 / 590 / 35.8%
    Cladosporium: 18 / 760 / 46.1%
    total: 62 / 2660

    living room:
    Aspergillus/Penicillium: 28 / 840 / 31.6%
    Cladosporium: 32 / 1400 / 52.6%
    total: 62 / 2660

    These numbers are relatively low, higher than the outdoor sample but still within the possible range of outdoor levels. We can see asp/pen in the outdoors up to about 1000 spores/m3 or so. I do not think this is evidence that more remediation is needed, I think you hypothesis about the carpet is a good one. I would have some additional HEPA air cleaning and also have the carpets cleaned with HEPA vacuums. You probably don’t need a top down cleaning but you could for extra piece of mind if you wanted.

    Hi Dylan,

    It would be greatly appreciated if you could help us interpret our results from a recent mold analysis from a air samples. We seem to have a Penicillium/Aspergillus problem, but we’ve not be able to find a source. The inspector/tester was unable to find a source but pointed out a few areas of potential. The inspector said the following, “Due to the abnormal levels of Penicillium /Aspergillus it
    is my recommendation that all porous materials such as carpet and fabric be removed and discarded.” Does that seem normal?

    Thank you for your time.

    (from the report) Source of Mold Growth: Previous leaks, high humidity

    (raw ct. spores/m3 %)

    Family Room
    Ascospores — 4 160 2
    Basidiospores — 22 880 9
    Cladosporium — 83 3320 35
    Penicillium/Aspergillus — 123 4920 52
    Smuts/Periconia/Myxomy — 3 120 1

    Ascospores — 21 840 9
    Basidiospores — 80 3200 33
    Cladosporium — 123 4920 51
    Curvularia 1 40 <1
    Epicoccum 1 40 <1
    Cercospora 1 40 <1
    Penicillium/Aspergillus — 3 120 1
    Smuts/Periconia/Myxomy — 2 80 <1

    Master Bedroom
    Alternaria — 1 40 <1
    Ascospores — 1 40 <1
    Basidiospores — 15 600 14
    Cladosporium — 9 360 9
    Curvularia — 3 120 3
    Nigrospora — 1 40 <1
    Penicillium/Aspergillus — 73 2920 70
    Smuts/Periconia/Myxomy — 1 40 <1

    I've already begun remediation of a few of the likely sources of humidity and I've got a dehumidifier in the basement.

    Results like this can be tricky to track down the source. Unless you have carpets or other porous materials that you can confirm have been wet and have mold growth, you do not necessarily need to discard them. I would start with having a detailed cleaning done, cleaning all walls floors and ceilings. While this is going on I would also have air scrubbers running to filter airborne mold from the air.

    I live in a building, can these mold have me sick? Here are my scores, thank you for your help and support.

    Aspergillus penicillioides 7
    Aureobasidium pullulans 161
    Chaetomium globosum 17
    Cladosporium sphaerospermum 3
    Eurotium (Asp.) amstelodami 19
    Paecilomyces varioti 2
    Cladosporium cladosporioides1 23
    Epicoccum nigrum 41
    Mucor amphibiorum 16
    Penicillium chrysogenum 19

    Hertsmi scored a 4
    Aspergillus penicillioides 7
    Chaetomium globosum spore 17 weighting a 4

    Hi Dylan!
    I would VERY much appreciate your take on just one result that was positive using Home Mold Lab/IAHA LAC. A reading of Asp/Pen 53 indoors (hyphal fragment) with 320 being the outdoor reading. I recently tested positive (urine) for mold, and am going through DMSA chelation (for 3 varieties of aspergillus as well as other ‘stuff’ (i.e., lead). I believe my mold exposure was prior to my current residence. Is there any reason to suspect that my current indoor reading (as low as it is) could be a possible contribution to ongoing health issues? Thanks in advance, Dylan! I so appreciate your time :^)


    That level is very low, we can see Asp/Pen in the outdoor air at 1000 spores/m3 at times! Homes with major Asp/Pen problems can be over 100,000 spores/m3, so your 53 seems normal.