Common types of indoor mold
Laboratory reports come back with genus names. Here is what the common ones are, where they usually turn up, and why the name is rarely the most useful part of the result.
The short answer
The species matters less than most people expect. The EPA's guidance is that all indoor mold growth should be removed and the moisture behind it corrected, regardless of the type. There is no species that is fine to leave and no species whose removal follows a different procedure.
What the name does tell you is something about the building. Some genera turn up on briefly damp surfaces; others are associated with material that has been wet for a long time. That is a clue about how far the water went and how long it has been there.
The genera you are most likely to see
Cladosporium
One of the most common molds indoors and out. Turns up on damp walls, ceilings, carpet and around window frames. Its presence usually points to condensation or a humidity problem rather than a burst pipe.
Penicillium
Common indoors, on damp building materials, wallpaper and insulation. Some species of the genus are the source of penicillin; the ones found in wet buildings are not doing anything useful there.
Aspergillus
Found indoors and outdoors, on food, soil and building materials. A large genus covering many species that behave quite differently from one another, which is why a report saying only "Aspergillus" is less specific than it looks.
Stachybotrys
The one usually called "black mold". Grows on wet cellulose material such as drywall, paper backing and timber. Its presence generally indicates material that has been wet for a sustained period, not a one-off spill — so finding it is a reason to look for a long-running moisture source.
Chaetomium
Also associated with cellulose material that has stayed wet. Frequently found in buildings after a leak has gone unnoticed behind a finish.
Alternaria
Mostly an outdoor mold, common in Florida air. Indoors it appears on damp surfaces near windows, in bathrooms and on carpet that has been wet.
Fusarium
Ordinarily a soil and plant mold. Indoors it is associated with materials that have been wet, particularly in humid conditions.
So why sample at all?
Sampling answers questions that looking cannot: whether what is airborne indoors differs from outdoors, whether a cavity you cannot open is contributing, and whether a cleaned area now matches its surroundings. It also creates a written record, which matters if anyone else needs to see the evidence later.
It does not answer "is this house safe". No sampling method can, and any laboratory result is a description of the sample taken, at that spot, on that day.
If growth is visible and the leak is obvious, sampling often just confirms what you can already see. We will say so rather than bill for it.
What we can and cannot tell you
The EPA and CDC both describe mold exposure as affecting people differently. Some people report symptoms such as a stuffy nose, sore throat, coughing, wheezing or irritated eyes and skin; others in the same building notice nothing. People with asthma, allergies or weakened immune systems may be more sensitive.
You will find pages online tying particular species to specific diseases. The CDC's position is that a causal link between so-called black mold and conditions such as memory loss or pulmonary hemorrhage has not been established. We are not going to tell you otherwise in order to sell a removal.
Questions we are asked
Do I need to know which species it is before removing it?
No. The removal is the same either way, and the EPA's guidance is to remove indoor growth and fix the moisture regardless of type.
Is black mold more dangerous than the others?
It is more strongly associated with material that has been wet a long time, which is useful to know about the building. The CDC does not support the stronger health claims commonly made about it.
Can you tell the species by looking?
No, and neither can anyone else. Color and texture overlap heavily between genera. That is what a laboratory is for.
Related
Mold removal vs mold remediation
Two words used interchangeably in marketing. The difference matters for what you should expect to be done, and what you should expect it to cost.
Read moreHow much moisture does mold actually need?
The humidity and temperature range mold grows in, why Florida sits inside it most of the year, and what to keep an eye on.
Read moreHave a question this did not answer?
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Florida licensed
Mold Assessor MRSA3298 and Mold Remediator MRSR3880, both held by Mauricio Gutierrez. Either number can be checked on the state register.
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