Molds are ubiquitous in nature, and mold spores are a common component of household dust. The term toxic mold is sometimes used to refer to mold-related indoor air quality problems.

Exposure to significant quantities of mold spores can cause allergic reactions. Under proper growing conditions, some species of molds may generate molecular compounds called mycotoxins. In large quatities or with chronic exposure, mycotoxins can be toxic to humans or animals.