If you have mold inside, you have experienced water intrusion or high humidity.
Mold requires five things to grow and must have all five ingredients.
Water; without water, or wet material you cannot have mold.
Food, generally a cellulose/fiber material - drywall, wood framing.
Temperature, the affected area temperature range of 70-95F.
Stagnant air, little to no air circulation.
Time; in 3-4 days, with the above ingredients, mold spores begin to develop.
Mold may not be visible, it could be on the other side of your drywall, under your carpet
or on wood framing,but it will grow given optimal growing conditions.