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Basidiospores - What are they?

1,200+ genera

Basidiospores Mold

Microscopic View Basidiospores Mold

Where would I normally find this type of mold?

Ubiquitous, Cosmopolitan. Distributed by wind and released during periods of high humidity or rain.

Where does it grow outside?

Gardens, forests and woodlands.

Where does it grow inside?

Dry rot, wood rot and brown rot are all the result of basidiospores producing fungi.  However, in the vast majority of cases, basidiospores detected in air samples are not from indoor growth.  They are typically brought in through windows and doors.  Because of this, mold remediation is typically not required.

Is this “black mold”?

The term black mold (also “toxic black mold”) is not scientific but is widely used by the media to usually reference Stachybotrys molds.

Health Concerns

Is it a potential allergen?

Some of people may experience hay fever, asthma, Lycoperdonosis and mushroom culture hypersensitivity.

Does it present any unique human risks? (as pathogen, opportunist or contaminant)*

Some reports have shown this to be the cause of opportunistic infections.

Can it produce toxins?**

Poisoning (toxicosis) is usually attributable to ingestion of mushrooms that produce the following toxins: amanitins, monomethyl-hydrazine, muscarine, ibotenic acid, and psilocybin.


Can it be identified via Air Sampling?

Yes.  However, Basidiospores are not indicative of an indoor mold growth problem.  While they are extremely common in the outside air, they do not grow well inside of homes.  Therefore, a high level of Basidiospores does not indicate your home has active mold growth.   These particular spore are found in very high quantities in the outside air.  They drift into your home via normal air leakage through windows, doors, clothing, pets, etc.   This often leads to mold test results with seemingly high levels of Basidiospores.  This should not be interpreted as a mold growth concern, but rather an indication of outside air infiltrating the home.  For those with mold allergies, this infiltration of Basidiospores can cause health issues.  Ideally, we prefer to bring fresh air into the home via a fresh air filter and pre-filter the air with the furnace filter.

Can it be identified via Direct Sampling?

Rarely identified except when sampling area of dry rot, wood rot or brown rot.

What are some of its industrial uses?

One species (A. pullulans) produce pullulan which is a biodegradable polysaccharide processed into fibers and used for packaging food and drug products.

Other comments:

Some mushrooms are non wood rotting and should be submitted to laboratory for accurate identification.

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is 52 spores / m to the exponent of 3 a high reading?

No, that is an extremely low reading.  In many areas, a typical outside sample of Basidiospores will show well over 1,000 spores per cubic meter.  Additionally, Basidiospores do not originate from fungal growth inside your home.  They are the product of forest organisms such as mushrooms, shelf fungi, etc.  They are not considered an indoor fungi/mold.  If Basidiospores are in your home (which is extremely common), it is because they floated in from the outside.


Is a raw count of 13 spores high for Basidiospores?

Definitely not.  Basidiospores are extremely common in the outside environment and almost always represent a source outside of your home.  Levels of 1,000-5,000 spores per cubic meter are quite common.  Note – it’s always best to look at the data in terms of spores per cubic meter vs a raw count.  The raw count is dependent on the sampling rate and time of the collection system.


I have 400 spore/m3 of Basidiospores inside my house - is it a harmful level?

No, this is not considered elevated in most climates/locations.  Additionally, basidiospores are nearly always from outside sources and do not indicate growth within the home.


I have high amounts of basidiospores in different rooms of my new home. Ranging from 5000 cubic meter to 18.0000. We cannot identify where they are coming from, our home is 1 year old and seemingly no leaks. Can you suggest where to look? We've added more filtration to our hvac system and this did not decrease the amounts - thank you

Basidiospores are nearly always the result of outdoor growth rather than an issue within the home. Occasionally house plants can lead to an issue, but this is rare.  Basidiospores are often found in very high numbers in the outside air.  Simply opening the front door and walking inside can bring in large quantities.  This is especially true if you live on a green belt, park, forest, etc.

The more responsible labs and inspectors will clarify this distinction about basidiospores in their reports.  Unfortunately, many do not.  This leads to many alarmed customers and unnecessary remediation.

If you’re not allergic to mold, there’s no reason to take any additional steps.  If you are sensitive, the best remedy is to focus on high quality air filtration (typically a 4″ pleated air filter on your furnace is best).  If you’ve already done this, run the blower/fan on your furnace 24/7.

Air sealing the home can also help reduce the influx of spores form the outside.  Be careful though, as this can lead to elevated humidity.


I question the test results I recently received from a local inspector.. Virtually nothing found in the outside higher spore and particles inside. 92% of inside are Basidiospores. We live in NC where it has been hot and humid and rainy here the past few weeks, again the results don't seem logical to me. I would love your expert opinion.

Basidiospore mold test results in home.

I agree – something does not look right.   Basidiospores are from fungi such as mushrooms, shelf fungi, etc. which do not grow indoors except under highly unusual circumstances (extreme saturation or overwatering indoor plants).

It is quite common to see basidiospore counts in the tens of thousands in the outside air.  My guess is the inspector accidentally switched the labels/cassettes.  I would ask for a retest before proceeding with any remediation.


Hello I have a level of 852 badiospores per cubic meter and 1-3 spores per slip from a surface sample. Does the surface sample indicate mold problem behind the walls that actually is problematic since there are physical spores in my bedroom?

In most parts of the country, those counts would be considered well below the threshold of concern.  Additionally, basidiospores are nearly due to an outside source of fungal growth.   They are the product of mushrooms and other types of fungi that are common outdoors, but very rare inside a home.  I recommend asking the lab for the average outside spore count data for basidiospores in your region.  A reputable lab, such as EMLab, should provide this information with your report.


I have a count of 5400 Basiospores per Meter cubed in a small dorm bedroom about 75 square feet. Is this an issue that requires concern?

In most cases, no, this is not cause for concern.  Basidiospores are almost always from outside the home (mushrooms and other fungi).  They rarely indicate an issue within the house.   There are occasions when basidiospores emanate from areas of heavy water damage and wood rot.  This is why an outside control sample is important.  In many regions a count of 5,400 spores would be considered very common for the outside air.