Molds are fungi that can be found both indoors and outdoors. No one knows how many species of fungi exist but estimates range from tens of thousands to perhaps three hundred thousand or more. Mold grows best in warm, damp, and humid conditions and spreads and reproduces by making spores. Mold spores can survive harsh environmental conditions, even dry conditions that do not support normal mold growth.

Some people are sensitive to mold or mildew. For these people, exposure to mold or mildew can cause symptoms such as nasal stuffiness, eye irritation, wheezing, or skin irritation. Some people, such as those with serious allergies to molds, may have more severe reactions like fever and shortness of breath.

Mold is found in virtually every environment and can be detected indoors and outdoors, year round. Mold growth is encouraged by warm and humid conditions. Outdoors it can be found in shady, damp areas or places where leaves or other vegetation is decomposing. Indoors, mold can be found where humidity levels are high, such as basements or showers.

Sensitive individuals should avoid areas that are likely to have mold, such as compost piles, cut grass, and wooded areas. Inside homes, mold growth can be slowed by controlling humidity levels and ventilating showers and cooking areas.