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The role of fungi (molds) in human disease

Robert Bush, MD
Section Editor
Bruce S Bochner, MD
Deputy Editor
Anna M Feldweg, MD


Concerns about the effects of exposure to indoor fungi on human health have become prominent in recent years. Fungi exposure can indeed cause adverse health effects, including infections, hypersensitivity disorders, and toxic/irritant effects from their by-products. Less clearly established are a variety of constitutional symptoms resulting from indoor mold exposure, including fatigue, nausea, cognitive dysfunction, and immune dysfunction, as well as putative syndromes such as "toxic mold syndrome" and "mold-induced immune dysregulation" [1-3].

Although "molds" is not scientifically accurate, it is a commonly used term for fungi. The terms "fungi" and "molds" are used interchangeably in this topic review. DNA-based studies have led to the taxonomic classification of fungi into eight phyla [4,5]. Most genera of fungi involved in human allergic diseases belong to three phyla, which are Ascomycota, Basidiomycota, and Zygomycota [6]. Previously, most fungi involved in allergic diseases where placed in the archaic group, Deuteromycetes-Fungi Imperfecti, the asexual stage of fungi.

Fungi that may be found indoors and outdoors, their proven and unproven health effects, and an approach to evaluating patients with symptoms that may be related to fungi will be discussed here.


Common species of fungi that can be found in the indoor environment include Cladosporium, Alternaria, Epicoccum, Fusarium, Penicillium, Aspergillus, and others (table 1).

The presence of fungal spores indoors typically results from invasion from outdoor sources, and indoor levels of fungus generally reflect the fungal levels occurring outdoors at the same time and place [7]. Outdoor fungi can gain access to the indoors via open windows or transfer on clothing or pets [8]. However, under the right conditions of humidity and temperature and in the presence of an adequate food source, fungal spores can proliferate indoors, independent of outdoor levels.


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Literature review current through: Jul 2017. | This topic last updated: Sep 10, 2015.
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