Cladosporium is Not Always Harmless

Cladosporium cladosporioides will frequently colonize on damp wood, while Cladosporium sphaerspermum will colonize on damp insulation

Recently, I reviewed several reports from other consultants who discounted the presence of Cladosporium in spore trap air samples, claiming that this mold was not of concern because it was the most common in the outdoor sample.  Following are a few reasons why their conclusions could be faulty:

  1. Cladosporium found in air samples is often considered non-problematic because Cladosporium is generally the most common mold found in outdoor air.  However, if there is actual growth of Cladosporium indoors, which would require excess unplanned moisture, other contaminants that are inherent to water damaged buildings will also be present.  When conditions exist for indoor mold and bacteria growth, endotoxins, mycotoxins, spores, glucans, and other allergens and inflammatory agents will be present.
  2. Generally, the first molds to colonize on wet building materials are Penicillium and Aspergillus.  These two genera cannot be differentiated in spore trap samples and are often under-reported.
  3. When only the genus can be identified in samples, as with spore trap methodology, indoor and outdoor fungal ecologies cannot be conclusively compared.  Cladosporium found outdoors might be Cladosporium herbarum, which is commonly found on decayed vegetation, while the Cladospoirum indoors could be Cladosporium sphaerospermum, which grows on water damaged insulation.
  4. Even if Cladosporium is the same species as outdoors, sensitized individuals could react when concentrations are elevated indoors.

Lesson learned:  Spore trap air sampling alone is a very inconclusive tool for assessing the moldiness of an indoor environment.  Claims that Cladosporium is not a problem can be faulty.


A detailed visual investigation is the single most important part of a mold investigation.  Sampling should only be performed to answer a question.  Spore trap samples cannot conclusively answer most questions.  A combination of air, dust, and surface samples that are analyzed by culturing or MSQPCR (Mold Specific Quantitative Polymerase Chain Reaction) is typically necessary.

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