Molds, like most fungi, can grow almost anywhere where moisture and organic material are available. In order to spread, mold releases spores which can spread through the air, water, or even on humans and animals.
Mold has a distinct, musty smell and appears as fuzzy, discolored, or slimy patches that increase in size as they grow. If you experience any of the above in your home, it means not only do you have a mold problem, it is also spreading.
Mold spreads rapidly where there is water (and water damage). That is why it is visible in bathrooms, shower stalls, bathroom tiles, and shower curtains, window moldings, the seal on the refrigerator door, surfaces on and around air conditioners, and in the attic.