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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

    My elderly mother has tested positive as having mold present/growing in her lungs. There is not an obvious sign of intrusion on their home (we had a contractor inspect besides our own walk throu
    gh) so we had someone come in and test the air last week. Preliminary summary is as follows (official report is being emailed tomorrow):

    “Bsmt 3,760
    1st 640
    2nd 1,040
    Attic 600
    Outside 480

    Bsmt and 2nd floor would be areas of counts considered to be high compared to outside

    No stachybotrys (black mold) was identified on any sample”
    (End of summary)

    I am wondering if you could offer any insight /suggestions. I suspect mom is more susceptable to mold allergens than most due to age (83), frailty (94 lbs), plus she is a former smoker who had a bout of severe pneumonia that hospitalized her when she was in her 30s.

    Their home (they’ve lived there 60 years) is always tidy but doesn’t really get the deep spring/fall cleanings as in their younger days.

    My thoughts are for us (offspring) to clean the basement and wash down surfaces with a mold killing concentrate and keep a dehumidifier running down there (unfinished basement with cement flooring, cement block walls and brick foundation). Deep clean the rest of the home and possibly run an air purifier on the 2nd floor where the bedrooms are /parents sleep. Would duct cleaning etc or anything else be helpful?

    We were shocked by the diagnosis because my folks have always maintained the home and readily addressed any repair issues etc.
    Any advice you can give is appreciated. Thank you, Barb


    “mold growing in the lungs” typically is a very specific infection. It would benefit you to find out if the infection is aspergillosis or a different type of fungal infection. Knowing this will help interpret the lab results. Stachybotrys isn’t an infectious mold, so the absence of that type does not help in interpreting the results. I would work with an experienced mold inspector who can perform viable mold sampling to figure out if infectious species such as Aspergillus fumigatus. It is key to find someone experienced with this kind of testing.

    With that being said, the types of mold that cause infections are found in the natural outdoor air and can affect susceptible people with minor exposure in the outdoors.

    I’m really concerned about my kitchen walls as they were never opened for 4 floods, Hurricane Harvey being 1 of them.

    Type Raw Count Spores %
    Basidiospores 4 267 <1
    Chaetomium 17 1130 <1
    Nigrospora 1 67 <1
    Penc/Aspergillus 2067 138000 99
    Rust/smuts/myx/perc 6 400 <1
    Stachybotrys 3 200 <1

    It may be a code red….but I would like some other insight

    These results are very high, I would recommend having a detailed inspection done in your home to find exactly where the mold is growing and have remediation done.


    The inspector did not take an outdoor control sample, so I can not say confidently if the asp/pen levels are elevated or not. The 1400 spores/m3 measured in the kitchen is within the potential outdoor range in your area, but it is higher than the other indoor samples so there is potentially a problem.

    Thank you. Would you say that the kitchen being dirty, under appliances and dirty ductwork could contribute to these particular elevated levels? The house has a screened in porch off the dining/kitchen area that has carpet that is wet from the snow. I don’t know if that area was opened and shut during the test, I can only assume due to the home inspection going on at the same time as the test.

    What steps/things to look for would I take to make sure this doesn’t become a huge problem?

    Hi Dylan,

    Was looking to purchase a home and due to issues with mold in a past rental, I had this new home tested during inspection. I am concerned that even ANY chaetomium is present in the air samples. It’s a heavy spore and just a few airborne spores can signify current or past water damage and a become a possible health issue correct?

    Chaetomium – 0
    Asp/Pen: Raw count: 12 Spores per M3 count: 80

    Inside elevated for both.

    Main floor:
    Asp/Pen: Raw count: 28 Spores per M3 count: 190

    Finished basement:
    Chaetomium – Raw count: 4 Spores per M3 count: 27
    Asp/Pen – Raw count: 60 Spores per M3 count: 400


    You are correct, Chaetomium is a large heavy spore and is abnormal to see in air samples. It is indicative of water damage, and it showing up in a finished basement tells me there is likely a history of water down there.

    We had a storm hit our home in March 2018. We have been fighting with the insurance company fighting over mold vs water damage. All adjuster reports show no visible mold in our home. The lab results show the mold higher outside than inside asp was a little over 16,000 outside and only 20 indoors. The insurance keeps saying the control is inside but I know the control is outside. So my question is Am I reading it wrong with those results is there extensive mold in my home or are they just trying to cap it off for mold which has a 15,000 limit vs what it would cost to fix the water damage. No one seems to know what they Interpretation would be for mold in your home.


    It would be very abnormal to have 16,000 asp/pen in the outdoor air (typically we can see asp/pen up to about 2,000 max outdoors). I would suggest hiring a local professional acting on your behalf to perform testing in the home.

    Is there any reason for concern in these results?

    OUTSIDE BASELINE (raw ct./per m3)
    Chaetomium- 0/0
    Cladosporium- 2/110
    Penicillium/Aspergillus types- 6/320

    Penicillium- 118/5300

    Chaetomium- 7/93
    Penicillium/Aspergillus types- 32/1700

    Cladosporum- 64/3400
    Penicillium- 122/2200


    there are elevated levels of Asp/Pen in all the indoor samples, and also the presence of Chaetomium in the nursery. These are signs of water issues in the home, and I would look into what could be causing these elevated levels.

    Hi Dylan,
    We are renting a property that the landlords finally had mold testing done after 3 months of knowing that there may be an issue. I arranged for the testing, they paid for it and now will not show us the report. This is what they have given us after requesting the report multiple times.
    ……They didn’t find any evidence of black mold anywhere in the house.
    Of the three rooms they tested, the basement was the only area that had significantly elevated mold spores relative to outside levels.
    the basement rated in the “moderate” range overall, with a “high” level of a specific type of mold called penicillium/asperillus (this is the same class of mold you sometimes find on bread – it can sometimes cause allergies, its what’s causing the musty mold smell). They recommend fixing the problem when total mold fall in the “high” or “very high” ranges.
    We know for a fact they they left out info. but they are unwilling to give us the report. My questions are do we have the right to see the report and our son has been having frequent upper respiratory issues, could this be coming from this type of mold.


    This blog is for help regarding interpretation of lab report data. I can not say if you are entitled to a copy of the report, or what health effects you could experience from unknown exposure. Sorry I can not be of more help to you.

    Hi Dylan-
    We are renting a single family home that apparently has a history of water in the basement. A year ago, we had the area tested and mold was found. The landlord cleaned the area himself and believes the problem solved. Now, a year later, we still believe there are issues and just repeated the tests. The results are as follows:

    Sample Vol: 25.00 liter
    Reporting Limit: 40 spores/m3
    Background: 2
    Fragments: ND
    Ascospores: 40/m3
    Basidiospores 120/m3

    Air from HVAC Register in Living Room:
    Sample Vol: 10.00 Liter
    Reporting Limit: 100 spores/m3
    Background: 2
    Fragments: ND
    Ascospores: 200/m3
    Basidiospores: 400/m3

    Basement Common Area:
    Sample Vol: 25.00 liter
    Reporting Limit: 40 spores/m3
    Background: 2
    Fragments: 80/m3
    Aspergillus/Penicillium: 1600/m3
    Epicoccum: 40/m3
    Myxomycetes: 80/m3

    Basement Bathroom:
    Sample Vol: 25.00 liter
    Reporting Limit: 40 spores/m3
    Background: 2
    Fragments: ND
    Alternaria: 40/m3
    Ascospores: 80/m3
    Cladosporium: 120/m3
    Myxomycetes: 40/m3
    Stachybotrys: 520/m3

    Would appreciate your opinion on whether – or how urgently – to insist the landlord hire a professional remediation company.

    Thank you

    The levels in the basement, specifically the aspergillus/penicillium and the stachybotrys are slightly elevated. At the very least a detailed cleaning and an inspection to check for hidden mold growth should be done. It is possible there is no remaining mold growth and the levels in the air are just residual from the past, however, there could still be hidden mold that should be addressed. A qualified inspector should assess the space.


    We recently had our air ducts cleaned, they of course found mold and insisted we have an air quality test performed. So we did. They did inside vs outside and everything inside was lower than outside levels, except for Cladosporium. Inside was raw count 4, &(Count/m3) 80…. and outside was raw count 3 & (Count/m3) 60…

    They of course said they recommend having our ducts replaced, but they didn’t explain really what the numbers meant. I’m wondering what our levels mean, if we are in danger or if it’s still a normal level, even though it’s slightly elevated compared to outside.. We have all had sinus issues and colds in and off since October but unsure if linked or just fun germs from our 3 year old and his classmates.

    Hi Dylan,
    I had a air quality test done at my home after I smelled something slightly off in my daughters bedroom and also found a roof leak. Long story short our levels in our house are as follows..
    Outside sample
    Medium Type: Micro5
    Exposure: 5.00 l/min. for 5.00 min. Reporting Limit: 40 Spores/cu. m

    Basidiospores 80 spores/cu.m
    Ascospores 40 spores/cu.m
    Total Fungi 120 spores/cu.m

    Opaque particles-very low

    Hall sample
    Smuts/Periconia/Myxomycetes 80 spores/cu.m
    Basidiospores 40 spores/cu.m
    Cladosporium 40 spores/cu.m
    Total fungi 160

    Dust debris-medium
    Opaque particles-low

    Pen/Asp group 720 spores/cu.m
    Basidiospores 80 spores/cu.m
    Total Fungi 800

    Dust debris-low
    Opaque particles- very low

    Should I be super worried? What effect does this have on our health and is it ok to stay in the home? I mean I’m sure this has been going on for a while and we had no idea. May be this is why we are all stuffy all the time. Thank you in advance for any advice.


    I do not see any issues with mold in these samples. The kitchen has a slight asp/pen elevation, but that could be due to potentially moldy food or garbage. In homes with major Asp/Pen issues we can see levels 10,000 spores/m3 and up to even over 100,000!

    Hi. I was wondering if you could evaluate my report:

    Altermaria Raw Count =1, M3 = 7 (outside zero on both)
    Ascospores Raw Count =1, M3 = 7, outside 7 and 47
    Aspergillus Raw Count = 3668, M3 = 24,453, Outside 14 and 93
    Cladosporium Raw = 7, M3 = 47, outside 91 and 607
    Rust Raw = 1, M3 = 7
    Total Raw = 3678, m3 = 24,520, Outside = 123 and 820

    1) How would you assess the following?:
    Sample # E140246R-1
    Medium Type: AllergencoD
    Serial #3153310
    Exposure: 15.00 1/min. for 5.00 min.
    Reporting Limit: 53 Spores/cu. m

    Sample Identification Raw Count Spores/cu.m Percent (%)
    – Fungi –
    Pen/Asp group 15 800 45.48%
    Basidiospores 12 640 36.38%
    Caldosporium 2 107 6.08%
    Ascospores 1 53 3.01%
    Mitospores 1 53 3.01%
    Smuts/Periconia/Myxomycetes 1 53 3.01%
    Torula 1 53 3.01%
    Total Fungi 33 1760 100.00%

    – Other –
    Hyphal Fragment 2 107 100.00%

    Background Item Level
    Dust / Debris Medium
    Hyphal Fragments Very Low
    Opaque Particles Low

    2) If the Pen/Asp represents 45% of the count and the Mitospores are 3%, should this be a concern to people or animals that plan to occupy the building?
    3) If it is a concern, what are mediation options, or is mediation even relevant or necessary when the entire building is going to be renovated?


    I live on a military base. So, mold. Unfortunately. An air sample picked up Chaetomium (in addition to others) in an area that has already been remediated and five minutes after the HEPA filters were turned off. Is any chaetomium a bad sign? Because they are saying “it’s normal.”

    Hi Dylan,

    Thank you for your help with everyone’s questions that are helpful to read. My question is regarding a quote from you in an earlier comment: “For wall cavity samples like these, there is not a need for an outdoor control. We typically look at the types and total concentration to make a determination. In a normal home without moisture and mold issues the total level of mold inside a wall cavity should be below 5,000 spores/m3 and not have any water damage indicators present.”

    So for indoor samples, for asp/pen category – if the indoor sample is going to be higher than outside, why would they compare outdoor readings, if those are usually non existent or low. The results and answers will always be “elevated” so how will I ever know what is good enough?
    Is it fair to say that a certain amount of spores/m3 in Asp/pen types specifically “normally” going to be found, Is there a way to guide someone to know that a reading of ie 1200-3900 can be acceptable, is somewhat normal, is not alarming, and not a cause for remediation. If you can say for a general guide if there is such a thing (a specified amount)? again you mentioned… below 5,000 spores/m3

    The quoted value of 5,000 spores/m3 is for wall cavity sampling, where we drill a small hole and directly sample from the inside of a wall, not for testing of the room air. When you collect samples from the air inside a room, the industry standard is to collect an outdoor sample and another indoor sample as well. These are used as guidelines in interpretation but are not a hard cut-off (ie if your indoor level is 1 spore higher than outside, the results are not necessarily elevated).

    For your specific example, the asp/pen levels are not always higher than outside, and there is still the need for the outdoor sample. Because the mold levels in Denver in December will be different than Florida in August we don’t have a guide for what “normal” mold levels are.

    Hi there,

    Was wondering what you think of my summary and spore trap test analysis:

    Basement FInished Area / Outside Summary:
    Moldscore – 196
    Exposure level – Basement: 960 and Outside 370

    Detailed Results:
    Overal Exposure Levels:
    Basement vs Outside:
    Penic/Asperg = 960 / 370
    Clado = 640 / <7
    Basid= 110 / 53
    Marker = <7 / <7
    Other = 81 / 54

    The two areas are basement finished area and outdoors:
    Spore Trap Analysis:
    Basement / Outdoors (all p/m3):
    Alternaria – 27 / zero
    Ascospores – 53 / 80
    Basid – 53 / 190
    Cladosporium – 110 / 53
    Epicoccum – 27 / zero

    You have a slight elevation of asp/pen and Cladosporium in the basement. To me, this likely means you have some chronic humidity issues down there and if you don’t see visible mold you can do a detailed cleaning of the space and run a dehumidifier to keep those humidity levels in check.


    Yes I do, it may take a while between responses, but when I get time I make sure that I get to everyone’s questions.

    Hi Dylan,

    I’m In the process of selling my house, seller had a mold inspection run and the I just received the results. the mold company said there were 8 “areas of concern” and mold tested 3 of these areas. They say that these 3 areas came back positive for mold. here are the results:

    Total Spore Count Count/m3

    Sample Results

    Office South Wall (Wall Cavity)

    Chaetomium 270 Cladosporium 770
    Other Brown 67 Penicillium/Aspergillus types 3,700 Smuts, Periconia, Mxyomycetes 130 Stachybotrys 1,300 Ulocladium 300 – positive

    Guest House North Wall
    (Wall Cavity)
    Chaetomium 110,000 Penicillium/Aspergillus types 53,000 Stachybotrys 700 Ulocladium 200 – positive

    Guest House Kitchen East
    (Wall Cavity)
    Chaetomium 14,000 Penicillium/Aspergillus types 49,000 Stachybotrys 6,000 Ulocladium 330 – positive

    What is your take on these results?

    I haven’t found any mention of any outside control samples taken, in which case, how seriously should I take this guys report?

    Many thanks!


    For wall cavity samples like these, there is not a need for an outdoor control. We typically look at the types and total concentration to make a determination. In a normal home without moisture and mold issues the total level of mold inside a wall cavity should be below 5,000 spores/m3 and not have any water damage indicators present. These results are all very high, and indicate there is mold growth in these wall cavities.

    Hello Dylan,
    Could you give me some assistance with the following numbers. They are out of my sons 12×10 Bed room. He is always trying to clear his through and/or cough. We took him to the doctor for allergies which led to the mold test.

    Name Spores per m3

    Alternaria (Ulocladium) 100
    Ascospores 100
    Basidiospores 610
    Cladosporium Species 90
    Curvularia Species 100
    Dreschslera/Bipolaris Group 50
    Hyphal Elements 90
    Myxomycete-Like 90
    Nigrosporea Species 50
    Pithomyces ++ 940
    Rusts 20

    Total 2240

    Could you please help me understand risk and what this means. We hired a hygienist and Wall cavity air was collected by cutting a small hole under a window and just above the base of 2 sliding glass doors. An air sample was taken outside as a baseline. We couldn’t afford all the other tests they asked us to do and just had them sample the areas that looked worse upon inspection. No visible mold anywhere only cracks in caulking and a little dry rot. We are renting and recently moved in and don’t know what to do. Thank you

    Chaetomium – 0
    Pen/Asp – 0
    Stachy- 0

    Other 3 areas tested as follows:

    Chaetomium – 22,644 – 12%
    Pen/Asp – 150,960 – 81%
    Stachy- 11,322 – 6%

    Chaetomium – 7,548 – 4%
    Pen/Asp – 150,960 – 94%
    Stachy- 1,887 – 1%

    Chaetomium – 15,096 – 3%
    Pen/Asp – 471, 750 96%
    Stachy- 0

    We can not establish any “risk” from inner wall samples. What inside the wall is not the air that you would be breathing.

    With that being said, these results are very high. This to me says there is an extensive water and mold issue inside of that wall cavity.

    We have our home on the market and have no signs of mold in our basement. Absolutely no spots, no musty odors. One day after putting the home on the market, we had a cash buyer (someone in the insurance business). My husband built our home and took precautions above and beyond to insure we would never have moisture issues in the basement. The buyer started asking questions about a very, very small crack in the mortar. We began to suspect they wanted out of the contract. Without knowledge of the buyer doing an air quality inspection, he had an inspection done. Last week we received a request to get out of the contract based on the air quality. Below are the numbers on the report:
    18,100 raw
    764,000 count/m2 and
    First of all, the report shows a date of collection prior to the date the potential buyer ever walked through our door. Secondly, we had two mold inspection companies come to our home and they found no visible mold and no smell. They indicated that with numbers like this they would have seen and smelled the mold. The second inspector did a thorough inspection and took more samples and we expect to have results on Tuesday. My question is, is it possible to have a count like this and no visible mold or a musty smell?

    These results are extremely high, you are not likely to get results higher than this in a home. It is not impossible to have these numbers and not see or smell mold (not all mold smells, and the smell is more of a function of moisture), the mold could be growing inside walls, or in microscopic colonies in things like carpet.


    We recently had a mold test done in our town home. We had two indoor air samples taken as well as a control. Results are listed below. They recommend doing additional exploration in the master bath due to the penicillium/Aspergillus count, but said all other numbers were normal. We had a leak about a year ago in the master bath, but we had a company come rip the walls out, dry and spray, and then fix it back up. All other counts were zero if they are not listed below. Would buying a nice HEPA filter and then cleaning the bathroom with appropriate chemicals do the trick for fixing?


    Outside Control (raw count/spores/m cubed/ %)
    Ascospores: 11/440/10%
    Basidiospores: 14/560/12%
    Cladosporium: 66/2640/58%
    Curvularia: 1/40/<1%
    Penicillium/Aspergilllus: 20/800/18%
    Smuts/Periconia/Myxomy: 1/40/<1%

    Den (raw count/spores/m cubed/ %)
    Ascospores: 1/40/7%
    Basidiospores: 6/240/40%
    Cladosporium: 3/120/20%
    Curvularia: 0
    Penicillium/Aspergilllus: 3/120/20%
    Smuts/Periconia/Myxomy: 2/80/13%

    Bathroom (raw count/spores/m cubed/ %)
    Ascospores: 2/80/5%
    Basidiospores: 5/200/12%
    Cladosporium: 3/120/7%
    Curvularia: 3/120/7%
    Penicillium/Aspergilllus: 28/1120/67%
    Smuts/Periconia/Myxomy: 0
    Pithomyces: 1/40/2%

    The bathroom asp/pen numbers are slightly higher, but not off the charts. Bathrooms with inadequate ventilation or minor moisture issues could have a result similar to what you have,

    I just has a mold inspection and sample done because we had a small water leak at our sliding glass door about 6 months ago. Mold was found under the carpet (cleaned and replaced about 2 months ago) and in the sheet rock/wall (found during the inspection). My family has been getting sick over and over for the past year so I have wondered if was because of our mold problem. My results came back today and the inspector says they are within normal levels. Can you take a look at the results and let me know? I’m concerned because I don’t see any Penicillium/Aspergillus in the outside control, only in our house.

    raw ct / spores/m3 / %

    Control – Outside
    Ascospres 1/40/1
    Basidiospores 61/2440/86
    Cladosporium 9/360/13
    Penicillium/Aspergillus —

    Living Room (where the mold was found)
    Ascospres —
    Basidiospores 7/280/28
    Cladosporium 8/320/32
    Penicillium/Aspergillus 10/400/40

    Kids Room
    Ascospres —
    Basidiospores 3/120/23
    Cladosporium 5/200/38
    Penicillium/Aspergillus 5/200/38

    Master Bedroom
    Ascospres —
    Basidiospores 2/80/25
    Cladosporium 3/120/38
    Penicillium/Aspergillus 3/120/38

    AC Register
    Ascospres —
    Basidiospores —
    Cladosporium 3/120/100
    Penicillium/Aspergillus —

    Thank you for your insight

    Nothing on these samples stands out to me. The asp/pen levels are very low, and just because it is not found outside in your sample, they can be found outside at levels up to about 1000 spores/m3. Thes results indoors are fairly low, and not likely from internal mold growth.

    Thanks for the wealth on information and time you donate. We appreciate it. I wouldn’t hesitate to book a phone consultation or recommend your services.

    In the process of purchasing a condo. I was interested enough in two units (miles apart) to have them inspected with air samples.

    Allergenco D Media was used in both tests.
    100% at 600X Magnification

    Raw / Count/m3 /%

    Unit 1


    Aspergillus/Penicillium-Like: 14 187 27%
    Memnoniella: 37 493 71%
    Smut/Myxomyces/Periconia: 1 13 2%

    Living Room
    Ascospores: 1 13 25%
    Cladosporium 3 40 75%

    Master Bed
    Cladosporium 3 40 100%

    I’m concerned about the outside. It’s Florida, I know hot and humid and an ideal place for mold and other things. The walkway (concrete) looks like black mold and needs cleaned by a fungacide and powerwashed.
    The inside numbers look low and acceptable to me.

    Unit 2
    This one scares me as I interpet the results as water damage combined with no A/C for over a year in Florida. Are outside numbers always elevated in hot/humid climates or could the results indicate a deeper problem with the buiding (units with outside entrance).


    Alternaria: 1 13 2%
    Aspergillus/Penicillium-Like: 54 720 83%
    Cladosporium: 7 93 11%
    Curvularia: 3 40 5%

    Aspergillus/Penicillium-Like: 1,008 13,440 100%
    Beltrania: 1 13 <1%

    Mater Bedroom:
    Aspergillus/Penicillium-Like: 1,161 15,480 100%
    Ascospores: 2 27 <1%
    Pithomyces: 2 27 <1%




    The second unit definitely seems to have some mold and or moisture issues. The first unit does not have anything that sticks out to me as an issue. Both outdoor samples look normal, the levels outside can change from day to day pretty drastically, but both are within what could be expected.

    Hi Dylan,
    We are in contract to purchase a home in the fog belt of the Northern California coast and noticed a musty smell. We learned that the house was used as a vacation home for decades so it had intermittent use until about two years ago. I have bad allergies and asthma, and had horrible health issues due to mold in a house about 10 years ago. It is a small house (1100 ft2) and the living room and master bedroom are at opposite ends of the house. There is some slight discoloration on the master bedroom ceiling but other than that no obvious mold within the house. They have a dehumidifier running in the kitchen. The floorboards in the two bedrooms are warped, and appear to have been that way for some time. The mold inspector suggests that because there is no obvious water intrusion or recent damage inside, that the mold is behind the drywall and/or in the ceilings.

    My questions are: 1. Would you recommend remediation efforts? 2. Would you recommend the whole house be treated? 3. If there is mold in the garage would that need to be dealt with too, i.e. could it spread into the house if we remediated that house but not the garage?

    Thanks so much for your time.

    We had a sample done and here are the results:
    Spores per cubic meter

    Ascospores 320
    Basidiospores 2,400
    Cladosporium 213
    Ganoderma 53
    Pen/Asp group 213
    Pollen 53

    Master BR
    Ascospores 53
    Basidiospores 373
    Cladosporium 213
    Epicoccum nigrum 53
    Ganoderma 53
    Pen/Asp group 3,470
    Smuts/Periconia/Myxomycetes 53
    Hyphal Fragment 53

    Living Room
    Basidiospores 480
    Cladosporium 320
    Ganoderma 107
    Pen/Asp group 7,150
    Smuts/Periconia/Myxomycetes 107
    Hyphal Fragment 267

    In situations like this, you can have microscopic growth on surfaces throughout the home, and it can be a large process to clean up. There are elevated levels of pen/asp in both samples, this type is consistent with what you have reported with homes that have been used infrequently in damp environments.

    The mold won’t spread from the garage if it is not treated.

    We built a home and moved in Nov 2018. In June 2019 I noticed visible mold in a bathroom cabinet that we rarely use since it was connected to the guest bedroom. After much frustration and to make a long story short, cabinet was removed which revealed lots of mold on the back and the bottom of the cabinet, on the drywall and visible rust on the drywall screws. Since that was taken care of, our flooring is reading various moisture levels with some visible water damage in 3 of the rooms. We have hardwood floors thruout the first floor except for tile in the bathrooms. Our septic was never installed properly and we are on a slab foundation so my husband assumes the foundation sucked up the 8 months of water and is showing it now in various places on our flooring. A mold company came in and did air sample tests and gave me the report. They never said if anything was concerning or not so I appreciate any of your feedback.

    Outside had sample volume (liters 75) with Debris Rating 1

    -raw CT: 8
    -spores/m3: 320
    -DL: 40
    %: 11

    Aspergillus/Penicillium- like
    – raw ct: 11
    -spores/m3:. 440
    DL: 40
    %: 16

    -raw CT: 51
    – spores/m3: 2,040
    DL: 40
    %: 73

    Main Living Room had sample volume (liters 75) and Debris rating is 2

    raw ct: 2
    spores/m3: 80
    DL: 40
    %: 1

    Raw ct: 12
    Spores/m3: 480
    DL: 40
    %: 5

    Raw ct: 102
    Spores/m3: 4,080
    DL: 40
    %: 45

    Raw ct: 68
    Spores/m3: 2,720
    DL: 40
    % 30

    Raw ct 2
    Spores/m3: 80
    DL 40
    % 1

    Raw ct 1
    Spores/m3: 40
    DL 40
    % <1

    Raw ct 13
    Spores/m3 520
    DL 40
    % 6

    Raw ct 12
    Spores/m3 480
    DL 40
    % 5

    Raw ct 12
    Spores/m3 480
    DL 40
    % 5

    Raw ct 1
    Spores/m3 40
    DL 40

    Raw ct 1
    Spores/m3 40
    DL 40
    % <1

    Raw ct 1
    Spores/m3 40
    DL 40
    % <1

    Other spores
    Raw ct 2
    Spores/m3 80
    DL 40

    Hyphal Fragments/cm2
    Raw ct 9
    Spores/m3 360
    DL 40

    In one of the bedrooms sample volume was 75 liters and debris rating 1

    Raw ct 16
    Spores/m3 640
    DL 40
    % 5

    Aspergillus/penicillium- like
    Raw ct 155
    Spores/m3 6,200
    DL 40
    % 47

    Raw ct 111
    Spores/m3 4,440
    DL 40
    % 34

    Raw ct 37
    Spores/m3 1,480
    DL 40
    % 2

    Raw ct 6
    Spores/m3 240
    DL 40
    % 2

    Other spores
    Raw ct 2
    Spores/m3 80
    DL 40

    Hyphal Fragments cm2
    Raw ct 4
    Spores/m3 160
    DL 40

    Aspergillus levels are elevated in both indoor samples, and there are also water damage molds (Chaetomium, Stachy, Ulocladium). I would have a professional look into the moisture issues in the flooring and bathroom.

    Thank you Dylan. Since the comment was posted we have had another mold test done. We are told we have to wait for the professional to determine the exact cause of the water/moisture issue before we can begin the remediation that has been recommended. In this report (same lab) showed no Chaetomium, Stachy or Ulocloadium. When I asked why some mold disappeared and other molds doubled in numbers, the response was that they arent sure what the difference was. I havent used bleach or mold sprays since I didn’t want to be the one doing the re-mediating. The Aspergillus/Penicillin increased slightly: raw ct. 176, 4,224spores/m3 and 24DL. Hyphal fragments have increased as well to raw ct. 23, 460spores/m3 and 20DL. we now have very small traces of Pithomyces and the Basidiospores has increased to 167 raw ct. 8,350spores/m3 and 50DL. Is this showing that the water/moisture issue has diminished and the mold has stopped growing to a concerning level? The outside numbers have spiked way high. All the inside numbers are lower than the outside except for the Asper/Pcn, Hyphal Fragments and Pithomyces. Thank you again!


    The change in the samples is likely just showing you how variable these things can be, not that the issues have been resolved. If you fix the water issues, the mold won’t disappear on their own for a very long time. The Asp/Pen numbers still are elevated and I would not consider these results an all clear.

    Recent air spore test on my sons small condo in South Florida. Your opinon please. Report says not to abandon the apartmen but to take remidation actions. Thank you Dylan.

    Outside Inside
    raw ct spores/m3 % raw ct spores/m3 %
    Ascospores 54 2160 31 3 120 5
    Basidiospores 99 3960 57 9 360 16

    Cladosporium 21 840 12 18 720 32

    Penicillium/Aspergillus 20 800 36

    Smuts/Periconia/Myxomy 1 40 2

    Stachybotrys 5 200 9

    The presence of Stachybotrys tells me there are mold and moisture concerns in the space. Things aren’t off the charts, but I would always tell people to trust their bodies over the numbers. If you don’t feel well in the space, try to leave. If you feel fine, you are probably fine staying around while things get remediated.

    Hi Dylan,

    I’m hoping you can provide some input on air quality test results recently done at my home. We originally decided to have an inspection done because we noticed a small amount of mold growing around light fixtures in several of our bedroom closets upstairs. In addition, I have always thought that the upstairs bathroom has had an odd smell to it since we moved in, but we never saw mold until now. Now there is a small amount of mold growing on the shower ceiling and some of the bathroom ceiling as well. We’ve only been here since January. The inspector came and didn’t seem to think the small spots on the closet ceilings were an issue, and just cleaned them off with some solution. He used a thermal imaging camera in the bathroom and didn’t note any concerns, and he didn’t say anything about the small amounts of mold on the ceiling in there. However the bathroom fan really doesn’t seem to work well and we assume the bathroom has humidity issues. I also think there is a musty smell in the upstairs level in general.

    We decided to get some air samples done because I am currently 7 months pregnant and I was worried since there was mold in the closet of the nursery bedroom. We had testing done in our upstairs level and basement. The upstairs sample was taken in a central location of the hallway, between the nursery and the bathroom. During the testing, the inspector opened and closed the bedroom doors and bathroom door a few times each to “create disturbances” as he called it. The results came back and there was Chaetomium found in the upstairs sample. The results were:

    13 spores counted, 173 spores/cu. m

    The original mold inspector called and said he wouldn’t recommend doing anything with those levels and that it was “low”. He insists that he thinks the spore count is due to a past leak since he didn’t find anything on his inspection and that he wouldn’t do anything for now except re-test in 6 months. After doing my own research online, I didn’t feel comfortable with his answer, especially since we have a newborn coming in less than 2 months. I called the lab that had processed the samples and the Dr. there suggested we get a HEPA purifier for the nursery and that we find the issue and remediate it.

    What is your opinion on the chaetomium level? Do you think that could be due to the mold growing in the bathroom shower and ceiling, or does it point to a larger issue? Should we have someone else dig deeper since the original inspector didn’t find any active moisture issues, or should we just have cleaning done? Do you have any recommendations on HEPA air purifiers for bedrooms? Sorry for the multiple questions…trying to get this all figured out ASAP before our newborn arrives as we don’t want to expose them to it. Thanks in advance!


    Those levels certainly suggest there have been some water issues in the space. Typically Chaetomium is the result of chronic water issues, beyond humidity issues. You could run the HEPA air purifier and do detailed cleaning and retest to see if the Chaetomium has been cleared from the air. To me, those levels indicate there is some amount of hidden growth, so you might need to have someone do a detailed inspection, cutting into walls, etc looking for the mold.

    I was not sure what exactly to share with you for your feedback. Thus, I’ve included screenshots of their first and second tests both from the outdoor sample and from the two indoor sample locations. If I need to set up a call or anything, do not hesitate to just let me know that.

    Outdoor 1:
    Main Living Room 1:
    Bonus Room 1:

    Outdoor 2:
    Main Living Room 2:
    Bonus room 2:

    These are the raw tables, I believe:


    The only thing that stands out to me is the low level of Chaetomium in the bonus room. Chaetomium is a water damage indicating mold and suggests there may be a history of water and mold issues.

    Hi Dylan:

    thank you for doing the work you do!!! I received my report from EMSL the basement boiler room was

    elevated raw count 314- of 13,900/m3 % total 87.4 aspergillus/pennicillium and –
    slightly elevated ascospores 200
    ” ” chaetomium 10
    ” ” Ganoderma 90

    The first floor lliving area was raw count 284- 12,600/m3 aspergillus/pennicillium 84.1%
    slighlty elevated levels of stachybotrys/memnoniella 40
    Cladosporium 530
    Pithomyces 40

    The basement area wet sheet rock and mold was removed before the air samples above were taken, should we go ahead and hire a mold remediation company and could the first floor living area been contaminated by the unprofessional remediation of the basement area? these numbers look high to me and is the aspergillus/pennicillum considered black mold and or toxic and at these levels dangerous for the residents to stay there?


    Not having an outdoor sample to use as a comparison, my interpretation is limited. It seems that Asp/Pen is elevated in both samples. Also, water damage indicating molds (Chaetomium and Stachybotrys) were found in both samples. I would look into having a professional evaluate the areas for additional mold and moisture problems, as well as additional cleaning/remediation.

    Good morning Dylan, I would greatly appreciate your input on these samples and whether I should be concerned and/or take any corrective action. Thank you. Tom Greto (I hope this email formatted the table as I laid it out; one can never be sure with these feedback forms.)

    Room/Area Description Sample Number Results
    Spore Density or Concentration Predominant Genus

    Air Samples

    Exterior -Air 1-2869 3648 2348 spores/m3 Basidiospores (1867)

    Mechanical room-Air 2-2869 3660 627 spores/ m3 Chaetomium (587)
    Stachybotrys (13)

    Basement-Air 3-2869 3656 220 spores/m3 Aspergillus/Penicillium (120)
    Chaetomium (33)
    Stachybotrys (13)


    Both the mechanical room and the basement have water damage indicating mold (both Stachybotrys and Chaetomium). I would look into what possible moisture issues are affecting the space and what needs to be done to address it as well as mold remediation.

    Hi…I work in a school and had air quality testing done in my office — which is very small space – maybe 10×10 with the following results reported:
    Ascospores: 1/40/4.6
    Aspergillus/Penicillium: 1/10/1.1
    Basidiospores: 1/40/4.6
    Chaetomium: 16/680/78.2
    Cladosporium: 3/100/11.5
    Total Fungi: 22/870/100
    Hyphal Fragment: 8/300
    Analyt. Sensitivity 600x: 42
    Analyt. Sensitivity 300x: 13

    Should I be concerned about the high levels of Chaetomium? I also had my own air purifier running in there before the same was collected – do you think that could have skewed the results? Thank you SO much for your time.

    I would be concerned about the Chaetomium levels, that is indicative of a moisture and mold issue. Running an air purifier could have an effect on the results, the results could be skewed low depending on how recent to the testing it was running.

    So thankful for the wealth of information on your blog. I myself am in the midst of selling a home and have recently had a test performed. I had a burst pipe in the room in question over 18 months ago but it was repaired and I THOUGHT dried appropriately. I have had 3 companies out to give estimates based on my test results and they have all said extremely differently things including, “let’s rip it all out and see what we are dealing with” to “well, your issue may be a foundation issue and even though you’re on a slab, your mold might be underneath your hardwoods – we can’t know until we rip it all up” and “you don’t need remediation.” I’m so confused. Results below:

    Acospores / 32 …1280 … 25
    Basidiospores / 55 …2200…43
    Cladosporium / 34…1360…26
    Epicoccum / 1…40…<1
    Cercospora / 2…80…2
    Rusts / 1…40…<1
    Smuts/Periconia/Myxomy / 2…80…2
    Zygomycetes / 2…80…2
    background debris: 3
    sample volume: 25
    total spores: 129/5160

    Acospores / 3…120…43
    Basidiospores / 2…80…29
    Cladosporium / 1…40…14
    ***STACHYBOTRYS / 1…40…14
    background debris: 3
    sample volume: 25
    total spores: 7/280

    I know the Stachybotrys is only present indoors so I have an issue somewhere but there is no visual mold is present based on mold inspector's report. An "elevated" moisture reading was noted on a vanity cabinet in the room but I am wondering if it's possible to tell from this test if I'm dealing with a relatively minor remediation or if there's a bigger issue at hand. I know you don't have a crystal ball but these tests are so hard to interpret. Thanks in advance for your time.

    When stachy results are this low, it is always difficult to interpret. I would not jump into any major remediation issues with only these results. I would investigate the moisture issue that was found, and maybe have some exploratory holes cut to investigate if there are mold issues inside the walls.


    Some labs differentiate spores which are found in clumps or chains, others do not. There is some logic behind the idea that spores which are clumped or chained together are closer to the source of growth than isolated spores, however, there is no actual research into this that I am aware of. I would pay much more mind to the levels of the molds, not if they are clumped or not.

    Hello, I am Real Estate agent and my client had mold air quality testing done. The following are the results of concern (higher inside than outside) Thank you very much for your time.
    Chaetomium INSIDE Raw =2, Count/m = 80, % of total = 15.1 OUTSIDE nothing
    Curvularia INSIDE Raw = 1*, Count/m = 10*, % of total = 1.9 OUTSIDE Raw = 1, Count /m = 40, %of total = 0.3
    Epicoccum INSIDE Raw =1, Count/m = 40, % of total = 7.5 OUTSIDE nothing
    Myxomycetes++ INSIDE Raw = 1, Count/m = 40, % of total = 7.5 OUTSIDE nothing
    Pithomyces++ INSIDE Raw = 2 Count/m = 80, % of total = 15.1 OUTSIDE Raw = 5, Count/m = 200, % of total =1.7
    Total Fungi INSIDE Raw = 13 Count/m = 530 %of total = 100 OYTSIDE Raw = 285, Count/m = 11610, %of total = 100

    Analyt. Sensitivity 600x INSIDE Count/ m = 41 OUTSIDE Count/m = 41
    Analyt. Sensitivity 300x INSIDE Count/ m = 13* OUTSIDE Count/m = 13*
    Skin Fragments (1-4) INSIDE Count/m = 2 OUTSIDE Count/m = 1
    Fibrous Particulate (1-4) INSIDE Count/m = 1 OUTSIDE Count/m = 1
    Background (1-5) INSIDE Count/m = 1 OUTSIDE Count/m = 1

    The only thing of note on the indoor sample is the presence of Chaetomium. The level is fairly low, however, this is a water damage indicator mold, meaning it is mainly only present in properties that have experienced some water damage.

    Thank you in advance for your time. We recently noticed wet carpet along one wall of our finished basement after very heavy rains. Pulling up the carpet and padding we noticed damage to the carpet tacks, indicating that this was likely not the first time there had been some water intrusion. My husband cut away the dry wall to look for the source and found a crack that was clearly the route for water entry, which is being repaired. There was also mold growth between the back of the drywall and the plastic sheeting separating the drywall from the insulation. He continued to cut away drywall and insulation until he had a clean margin. We had a mold inspector come just to be safe, and while he found no levels of moisture anywhere in the home that would support mold growth, no smell and didn’t find any visual evidence of remaining mold growth (he even reached up behind where we had cut the drywall away and looked/felt around and found nothing), he is recommending a full remediation of the basement because there was one spore of chaetonium and three hyphal fragments on the air sample. He said it could just be residual from when we cut the drywall to find the leak (and cut out everything moldy) but it’s an automatic test failure if chaetonium is present at all. He also took the control sample from our front sidewalk away from the house, but the basement has a walkout that backs up to a ravine with lots of vegetation and seems to be a better ‘control’? We want to follow the correct procedure but not overkill, appreciate your thoughts.

    Outside – Sample vol 25L
    Basidiospores 63 raw /2520 per m3 / 83%
    Cladosporium 1 / 40 / 1
    Curvularia 2 / 80 / 3
    Smuts/Periconia/Myxomy 2 / 80 / 3
    Zygomycetes 7 / 280 / 9
    Pithomyces 1 / 40 / 1
    Background debris 3
    Total spores – 76 / 3040

    Basement – Sample vol 25L
    Hyphal Fragments 3 raw / 120 per m3
    Ascospores 8 / 320 / 21
    Basidiospores 13 / 520 / 33
    Chaetomium 1 / 40 / 3
    Cladisporium 11 / 440 / 28
    Epicoccum 1 / 40 / 3
    Pennicillium/Aspergillus 4 / 160 / 10
    Pithomyces 1 / 40 / 3
    Background debris 3
    Total spores – 39 / 1560

    Different inspectors have different thresholds for what would be a “failure”. It is difficult to say if a single spore is evidence of additional areas of mold growth or if it is left over from your husband cutting out the moldy drywall. I would suggest retesting before doing any further remediation.

    The outdoor sample would not be much different in the back of the home or the front. Due to air movement outdoors, the mold in the air is influenced from all over, not just the immediate area. Also, Chaetomium would not typically show up on any outdoor sample, which is why the inspector noted that a single spore result stands out.

    Hello we just got mold testing done in our basement due to a water leak from a window. The company first recommended an air test and the results came back as:
    Aspergillus/penicillium: 13173 count/m3
    Chaetomium sp: 4800 count/m3 (mold company concerned about number)
    Cladosporium sp: 2080 count/m3
    Stachybotrys sp: 373 count/m3 (mold company concerned about number)
    Basidiospores 107 count/m3

    All other levels were under 100/m3

    I feel like they mold company is trying to get the most money out of us as possible. They didn’t do a surface test even though we knew where the water was coming in. They want us to spend a lot more money now to do some remediation and then another $400 airs test. I was just searching for help to try to understand this all. Thank you!

    I would echo their concerns about the Aspergillus, Chaetomium, and Stachybotrys levels. Those are all very high results.

    I am in the inspection period of a home purchase. I had a regular inspection done but I also did my own ERMI. Concerned now that I have results back……
    Aspergillus ochraceus = 215
    Penicillium corylophilum = 68
    which puts the house at a ERMI 10.4 = Q4 red. ack!

    Aspergillus penicillioides = 99 (4 points)
    Wallemia sebi (0 points)
    so this comes out to a 4 which is considered “fine”

    Why does the ERMI says Q4 (almost at the top and serious) but the HERTMSI says basically okay?

    Help! A confused potential homeowner. Thank you!

    This blog is to help interpret the results of air sampling for mold, not DNA based tests like ERMI. HERTSMI is only looking at 5 species of mold, where ERMI is looking into 36 species of mold.

    Hi. Thank you for the clarification. I am new to this! So, in your opinion, should I have done an air test instead of the ERMI?

    Hello. I had mold testing done in our rental house. Air analysis detected penicillium/Aspergillus with a raw count of 3,764 and 50,061 for cubic sq ft. Also detected was Cladosporium growth of 670,598 sq. Is this a dangerous toxic level for humans or pets. I have a compromised immune system due to cancer and haven’t felt good lately but noticed I feel better when not in house. Help me understand the levels as I feel my landlord was aware prior to me moving in 6 months ago and is acting like it’s ok and not to b concerned.


    These numbers are very high. I am not a medical professional, so I can not assess if any amount is “safe” or “harmful”, but I can say that both Asp/Pen and Chaetomium levels are highly elevated, and an indication of moisture and mold growth in the property.

    Amazing you provide such valuable feedback! Here’s my house results after water intrusion from toilet overflow. Thank you, thank you in advance. Medium Type: Air-O-Cell; Exposure: 15.00 l/min. for 5.00 min; Reporting limit: 53 spores/cu. m

    Outside: Raw Count: 29 Spores/cu. m: 1,550
    Bed 1: Raw Count: 1 Spores/cu. m: 53
    Bed 2: Raw Count: 1 Spores/cu. m: 53
    Outside: Raw Count: 6 Spores/cu. m: 320
    Bed 1: N/A
    Bed 2: Raw Count: 1 Spores/cu. m: 53
    Outside: Raw Count: 4 Spores/cu. m: 213
    Bed 1: Raw Count: 2 Spores/cu. m: 107
    Bed 2: N/A
    Hyphal Fragment
    Outside: N/A
    Bed 1: Raw Count: 1 Spores/cu. m: 53
    Bed 2: Raw Count: 1 Spores/cu. m: 53
    Outside: N/a
    Bed 1: N/A
    Bed 2: Raw Count: 2 Spores/cu. m: 107
    Outside: Raw Count: 1 Spores/cu. m: 53
    Bed 1: N/A
    Bed 2: Raw Count: 2 Spores/cu. m: 107

    The Chaetomium found in Bed 2 is a yellow flag to me. Chaetomium is an indicator of water damage and is a toxigenic fungi.

    Thank you. A mold inspection consultant provided a certificate of mold damage remediation specifying that the property did not contain evidence of mold damage (despite the report showing 2 spores of chaetomium found in the bedroom) – should that be sufficient? Or do I need to request written documentation from the consultant saying chaetomium was actually cleared? There was water damage from a toilet overflow into that bedroom that is said to have been remediated. Would not the chaetomium need to be cleared?


    Since there are no regulations or guidelines determining what a normal amount of mold indoors is, consultants have to use their experience and professional judgment when writing reports. In my professional opinion, I would not have written a post remediation verification letter with the Chaetomium present.

    I have had three mold tests done.

    The first showed 427/m3 Aspergillus/Penicillium in the HVAC system. We were told the problem was identified and fixed. The vent was cleaned and sterilized. Two weeks later, a second test was peformed, and it showed 147/m3 Aspergillus/Penicillium. On both days, the outdoor control sample contained NO DISCERNIBLE AMOUNT of Aspergillus/Penicillium. I was told that 147/m3 was an acceptable level and not a concern.

    22 days after the second test, a third test was conducted and showed 270/m3 Aspergillus/Penicillium. Again, there was NO DISCERNIBLE AMOUNT of Aspergillus/Penicillium in the outdoor control sample. I think we have a problem that has not been properly fixed as of yet.

    What I really need to know though is this: are any of these numbers an “acceptable” level really? What could be causing this in the HVAC system? The numbers I shared are from one room in particular that consistently reads high in these spores. Other rooms also have elevated levels of Aspergillus/Penicillium, but at lower levels like 27 in the living room on the day 427 was recorded in a bedroom during the first inspection, and 200 in the living room on the day 270 was recorded in the same bedroom. The living room and the bedroom are on different floors of the home. Is this something I need to worry about? Now that we know there IS mold, what do we do to find the source? I thought we already took care of it, but now it seems the problem was only temporarily abated. What do we do now?


    This is a very specialized situation, where someone like me could not say if it is acceptable or not. Depending on where in the HVAC system the samples were taken, the style of HVAC system and the filter used, and many other variables can play a role in how to interpret the results.