A mold is a microscopic fungus that grows and lives on plant or animal matter or on non-organic objects. Most molds are made up of filaments and reproduce through the production of spores, which spread by air, water, or insects. There are many thousands of species of fungi.
Mold growth is encouraged by warm and humid conditions.
Outdoors, they are commonly found in shady, damp areas where vegetation is decomposing. Indoors, they can be found where humidity levels are high, such as basements or showers. Molds cause allergic symptoms in many people. More severe reactions may occur among workers exposed to large amounts of molds in occupational settings, including fever or shortness of breath. In people who have chronic illnesses, such as obstructive lung disease, mold infections may occur in their lungs.