Molds are various fungi that often cause disintegration of organic matter. No one knows how many species of fungi exist but estimates may range in the hundreds of thousands. Molds grow best in warm, damp, and humid conditions, and spread and reproduce by making spores. However, mold spores can also survive harsh environmental conditions, such as dry conditions, that do not support normal mold growth.

Mold is found both indoors and outdoors. Mold can enter your home through open doorways, windows, vents, and heating and air conditioning systems. Mold in the air outside can also attach itself to clothing, shoes, bags, and pets can and be carried indoors. It will grow in places with a lot of moisture, such as near windows, near pipes, around leaks in roofs, or where there has been flooding. Mold grows well on paper products, cardboard, ceiling tiles, and wood products. Mold can also grow in dust, paints, wallpaper, insulation, drywall, carpet, fabric, and upholstery.

All molds have the potential to cause health effects. Molds can produce allergens that can trigger allergic reactions or even asthma attacks in people allergic to mold. Others are known to produce potent toxins and/or irritants. For some people, molds can cause nasal stuffiness, throat irritation, coughing or wheezing, eye irritation, or, in some cases, skin irritation. People with mold allergies may have more severe reactions. Immune-compromised people and people with chronic lung illnesses, such as obstructive lung disease, may get serious infections in their lungs when they are exposed to mold.