Mold (fungi) is present everywhere.

There are more than 100,000 species of mold.

Molds are organisms that may be found indoors and outdoors. They are part of the natural environment and play an important role in the environment by breaking down and digesting organic material, such as dead leaves. Also called fungi or mildew, molds are neither plants nor animals; they are part of the kingdom Fungi.*

Mold is not usually a problem indoors—unless mold spores land on a wet or damp spot and begin growing. As molds grow they digest whatever they are growing on. Unchecked mold growth can damage buildings and furnishings; molds can rot wood, damage drywall, and eventually cause structural damage to buildings. Mold can cause cosmetic damage, such as stains, to furnishings. The potential human health effects of mold are also a concern. It is important, therefore, to prevent mold from growing indoors.*

Inhalation exposure to mold indoors can cause health effects in some people. Molds produce allergens (substances that can cause allergic reactions), irritants, and, in some cases, potentially toxic substances or chemicals (mycotoxins). Inhaling or touching mold or mold spores may cause allergic reactions in sensitive individuals. Mold does not have to be alive to cause an allergic reaction. Dead or alive, mold can cause allergic reactions in some people.*

Mold frequently grows in hidden places – behind wall linings, in floors or behind installations and is often not visible from the outside. When moisture builds up from leaky pipes or roofs, high humidity, or flooding, conditions are ideal for mold growth. Molds are easily disturbed and their spores can become airborne, getting into noses, mouths and lungs. Allergic reactions to mold are common and can be immediate or delayed. Repeated or single exposure to mold, mold spores, or mold fragments may cause non-sensitive individuals to become sensitive to mold, and repeated exposure has the potential to increase sensitivity. Allergic responses include hay fever-like symptoms such as headache, sneezing, runny nose, red eyes, and skin rash (dermatitis). Molds can cause asthma attacks in people with asthma who are allergic to mold.
In addition, molds can irritate the eyes, skin, nose, throat, and lungs of individuals
whether or not they are allergic to mold.*

*Referenced EPA.