Mold (fungi) is present everywhere indoors and outdoors. There are more than 100,000 species of mold. At least 1,000 species of mold are common in the U.S. Some of the most commonly found are species of Cladosporium, Penicillium, and Aspergillus. Mold is most likely to grow where there is water or dampness, as in bathrooms and basements.