They are ubiquitous in all terrestrial and freshwater and marine environments, and grow in plants, soil, water, insects, cattle rumens, hair, and skin.
Penicillium species are used in the manufacture of blue cheeses and as the source of the antibiotic penicillin, discovered by Sir Alexander Fleming in 1928, while Fusarium venenatum is used to produce Quorn, a mycoprotein food product.
[citation needed] Microfungi can be harmful, causing diseases of plants, animals and humans with varying degrees of severity and economic impact.
Microfungi may cause diseases of crops and trees which range in severity from mild to disastrous, and in economic importance from beneficial to seriously costly.
In the built environment, the toxic fungus Stachybotrys chartarum causes damage to damp walls and furnishings, and may be responsible for sick building syndrome.