Cladosporium is the most common culturable mold genera found in the world(1,2), found anywhere from the Amazon to the Arctic. Cladosporium grows in colonies that are dark in color, ranging from black/brown to green. In the outdoors, Cladosporium commonly grows on decaying plants and soil. Natural levels in the outdoor air vary greatly by season, with very high numbers in the summer, and low numbers in the winter. Indoors, this fungi is a type that we see in areas with chronic high humidity, such as a poorly ventilated bathroom, or a damp basement. If you have ever seen the dark stains along the grout lines in a shower, in my experience, that is most likely Cladosporium.
When sampling the air for mold, Cladosporium levels are often difficult to interpret indoors because it naturally occurs in the outdoor air at high levels. A major limitation of the most common air sampling technique is that it only identifies the genus, such as Cladosporium, but is unable to identify the species, such as Cladosporium sphaerospermum. The overall levels in the outdoor air and indoor air may be similar, however the Cladosporium indoors may be a different species. Since spore trap sampling can not identify mold to the species level, this could result in a “false-negative” interpretation.
Cladosporium is not thought of as being a pathogenic or a toxigenic fungi. However, like all molds, it can cause allergic reactions in sensitive individuals as well as being an asthma trigger.
- Hedayati, M.T., Mayahi, S., Aghili, R., Goharimoghadam, K. (2005). Airborne Fungi in Indoor and Outdoor of Asthmatic Patients’ Home, Living in the City of Sari, Iranian Journal of Allergy, Asthma, and Immunology, 4, 189-191.
- Shelton, B. G., Kirkland, K. H., Flanders, W. D., & Morris, G. K. (2002). Profiles of Airborne Fungi in Buildings and Outdoor Environments in the United States. Applied and Environmental Microbiology, 68, 1743–1753.