Molds are microscopic fungi that are found naturally in the environment. Molds can be found almost anywhere; they can grow on virtually any organic substance, as long as moisture and oxygen are present. There are molds that can grow on wood, paper, carpet, foods and insulations. When excessive moisture accumulates in buildings or on building materials, mold growth will often occur. It is impossible to eliminate all mold spores in the indoor environment. However, mold growth can be controlled indoors by controlling moisture. Mold spores waft though the indoor and outdoor air continually. When mold spores land on damp soot indoors, they may begin growing and digesting whatever they are growing on in order to survive.

Since mold requires water to grow, it is important to prevent moisture problems in buildings. Moisture problems can have many causes, including uncontrolled humidity. Some moisture problems in buildings have been linked to changes in building construction practices during the 1970s, 80s, and 90s. Some of these changes have resulted in buildings that are tightly sealed, but may lack adequate ventilation, potentially leading to moisture buildup. Building materials, such as drywall, may not allow moisture to escape easily. Moisture problems may include roof leaks, landscaping or gutters that direct water into or under the building, and invented combustion appliances. When mold growth occurs in buildings, adverse health problems may be reported by some of the occupants, particularly those with allergies or respiratory problems. .