Brown hairy mold in bathrooms (and on OSB subfloors):
this document gives advice on identification of and health risks of brown hairy mold found in bathrooms (and other building areas), including brown hairy Stemonitis sp. mold found on bath floor tiles, under carpeting, on wood subflooring.
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Here we also discuss how to address the risk of further hidden bathroom mold, and we cite references on the toxicity of Stemonitis sp. - a brown hairy myxomycete mold found on OSB, wood subfloors, and in some bathrooms such as the bath floor shown in our page top photograph.
This article series helps identify the presence of or locate the probable sources of mold reservoirs in buildings, and helps decide which of these need more invasive, exhaustive inspection and testing.
Question: what is this hairy brown mold found in my bathroom? Is brown hairy mold dangerous? How do I get rid of it?
I live in Melbourne Australia and I have a major issue with my bathroom floor. Please see my brown hairy mold photographs (below). The images are of brown mold growths on the bathroom floor, & afterwards when I had scraped them off the floor.
I do understand that no competent expert would pretend to ID mold [or any other microscopic particle] from just a field photo.
But I have no idea what I'm dealing with and of course am concerned for my health and my family's. Can you tell me please - is brown hairy mold dangerous? When I scraped the protrusions off the bathroom floor, it turned into a powder & hair like structures stood on end. I would be most grateful if you could please tell me what this could be and if it is dangerous.
I'm wanting to send a specimen away for analysis & hope that I can locate a government organisation in Australia, such as the Agricultural Department, hopefully they can do this at no cost. - G. P., Melbourne, Australia
Reply: Examination of fungal material in an aerobiology lab is needed for sure identification of mold
But with that caveat stated, the pattern and character of the mold in your photos resembles like a fungus Stemonitis sp.  -
see BROWN MOLD PHOTOS and also at Rental Apartment Mold Safety Advice where we include photographs of Stemonitis sp. found on a bathroom floor and growing on oriented strand board (OSB) or "waferboard" in a basement.
Enlarging your photos [click any image to see an enlarged version] we see the mold was thick under carpeting (above left) meaning that in at least this area of the building, mold growth, including in hidden cavities such as walls, floors, ceilings, is likely to be extensive.
Watch out: And one would certainly expect other leak damage; that "wrinkled" looking floor baseboard trim board - if that's what it is in photo #1 at above left - means there have been leaks and probably rot.
If the mold test lab or aerobiology lab technician who examines a mold test sample you provide is familiar with myxomycetes, s/he should easily recognize the fungus from an actual sample. - you can use the clear adhesive tape sampling procedure at TEST KITS for DUST, MOLD, PARTICLE TESTS and send the sample to a qualified local lab of your choice [not to us]. But as I comment below, you probably do not need to test this mold.
Action: remove the mold and fix the cause for its growth in the first place.
Many Brown Hairy Molds are Probably Harmless
Stemonitis sp. is a Myxomycete ( a class of fungus) that is not listed in our MOLD ATLAS & PARTICLES INDEX
nor in the authoritative Atlas of Clinical Fungi, deHoog et als. as a known toxic mold, though it is commonly described in mushroom field guides such as the National Audobon Society's Field Guide to Mushrooms 
But as we warned you earlier, having so much fungal growth and leakage as we saw in that lifted-carpeting photo, you should expect that other genera/species are likely to be present even if you don't see them yourself from a superficial inspection.
Watch out for Other Leaks & Hidden Mold
Watch out: At a minimum you'd be smart to assume there are allergenic molds present and if there is more than about one square meter of moldy material, to use appropriate protection measures during cleanup as well as, of course, finding and correcting the leaks that led to these conditions.
It is not usually necessary to test mold to identify the genera species. That will not change how mold should be removed or prevented in buildings.
On occasion, for medical reasons or for control of a costly mold remediation project, there are reasons (MOLD TEST REASONS) to identify mold in buildings.
As we explain at BATHROOM MOLD, mold may be found growing on wood subfloors under bath floor tiles or sheet vinyl flooring if the bathroom floor has been wet or flooded. If a ceramic bath tile floor has become loose or if bathroom floor carpeting has been wet (as one would expect), we suggest exploring for damaged subfloors - otherwise simply repairing the tiles or replacing moldy carpeting may not be a durable fix.
If the bathroom is not on a basement or slab, inspect the ceiling areas below the bathroom for leak stains. Stained areas of drywall ceiling below a leaky bathroom or bath fixture usually merit further investigation.
You will want to study the building carefully to decide on the building points at most risk of having been wet from leaks due to construction details or other site observations. That's where one would make a test cut, remove carpeting, or otherwise explore further for hidden mold.
See ACTION GUIDE - WHAT TO DO ABOUT INDOOR MOLD on what to do about mold
Reader Question: what is this brown stuff on my window sill?
These 2 brown blobs were discovered on a window sill at home that were not there 3 days before due to the room being cleaned out for guests (ie must have been very fast growing).
Each measured approx. 2 inches long x ½ inch high x ½ inch wide.
My house is constructed from concrete filled reinforced blocks that has 8 inch thick walls. Whilst cleaning them up I noticed they had a vertical spore formation and had very fine chocolate brown coloured dust. Any information would be much appreciated.
Regards, R.C. 11/21/2013
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website. In particular, take a look at some of my Stemonitis photos at BROWN HAIRY BATHROOM MOLD.
That fungus, often found in buildings, has different appearances depending on its age, growth substrate, and environmental conditions. It can become a brown blobby mess. The stuff in your photo - well there is just no detail for me to examine.
All I can make out in your photo is a pair of brown blobs. But if at different points in the material's life cycle it looked like my Stemonitis then that may be what it is. I have found this fungus growing on bath tiles at grout joints, and on OSB subflooring in bathrooms and occasionally in other building areas.
The Stemonitis sp. itself is not a particular health worry. But I'd be looking for a hidden leak at the window sill and possibly other hidden water damage.
Also see BROWN MOLD PHOTOS for more general questions and answers about brown mold found in buildings and an answer to "should I buy a home that has a mold problem?"
Continue reading at MOLD BEHIND MARBLE or TILE or select a topic from the More Reading links shown below.
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