Mold is a type of fungus which typically grows in colonies on various kinds of damp or decaying organic matter. To grow and spread on it needs enough moisture. There are many different mold species which come in a variety of different colors – from snow white to black. Black, white, dark green and grey shades are the most popular colors of mold. They have a very distinctive odor: earthy, or urine scented.
You can find mold both indoors and outdoors in all climates, during all seasons of the year. Outdoors, molds survive by using plants and decaying organic matter such as fallen leaves as a source of nutrition. Indoors, molds need moisture to grow as well as a carbon source from building materials or building contents. Like all types of fungi, also molds thrive in places of high humidity and warmth – including closets full of clothes, bathrooms, kitchens and cellars. Other potential hiding places for molds are leaks in roofs, windows with a lot of moisture, or pipes where there has been flooding and insufficient drying afterwards. Mold grows well on paper products, cardboard, ceiling tiles, and wood products. It can also grow in dust, paints, wallpaper, insulation, drywall, carpet, fabric, and upholstery.
There are thousands of mold species known to science. Some of them are harmless or even beneficial for our ecosystem, playing an important role in biodegradation or in the production of various foods, beverages, antibiotics and enzymes, whereas other species are dangerous and cause allergies, respiratory illnesses and immune system problems. Alternaria and Cladosporium are the molds most commonly found both indoors and outdoors throughout the United States. Aspergillus, Penicillium, Helminthosporium, Epicoccum, Fusarium, Mucor, Rhizopus, and Aureobasidium are also common.