Molds are commonly found in buildings and homes, and will grow in places with a lot of moisture. It can grow on paper products, cardboard, ceiling tiles, and wood products, as well as in dust, paints, wallpaper, insulation, drywall, carpet, fabric, and upholstery. Mold can enter your home through open doorways, windows, vents, and heating and air conditioning systems. Mold in the air outside can also attach to clothing, shoes, and pets.
Exposure to damp and moldy environments may cause a variety of health effects, or none at all. Some people are sensitive to molds. For these people, exposure to molds can lead to symptoms such as stuffy nose, wheezing, and red or itchy eyes, or skin. Some people may have more intense reactions, such as fever or shortness of breath.
Inside your home you can control mold growth by controlling humidity levels, fixing leaks, thoroughly cleaning and drying after flooding, and maintaining proper ventilation (especially in areas with high moisture). Consider not using carpet in rooms or areas like bathrooms or basements that may have a lot of moisture.
In some cases, professional mold testing and mitigation may be required. (Info from CDC website: https://www.cdc.gov/mold/faqs.htm