The first thing to understand about mold is that there is a little mold everywhere – indoors and outdoors. It's in the air and can be found on plants, foods, dry leaves, and other organic materials. It's very common to find molds in homes and buildings. After all, molds grow naturally indoors. And mold spores enter the home through doorways, windows, and heating and air conditioning systems. Spores also enter the home on animals, clothing, shoes, bags and people.