It’s not really practical to expect a building to be completely free of mold, nor is it always necessary. However, mold growth on indoor surfaces is generally a sign of excess moisture in the air, and the source needs to be identified and corrected. Left unchecked, the mold problem will definitely worsen.
Water in your home can come from many sources. Water can enter your home by leaking or by seeping through basement floors. Showers or even cooking can add moisture to the air in your home. The amount of moisture that the air in your home can hold depends on the temperature of the air. As the temperature goes down, the air is able to hold less moisture. This is why, in cold weather, moisture condenses on cold surfaces (for example, drops of water form on the inside of a window). This moisture can encourage biological pollutants to grow.
By maintaining proper humidity levels in your home, you will reduce the chance that mold can grow. If you are noticing excessive moisture on windows or other cold surfaces, your home humidity level is too high. Consider options to reduce the humidity levels such as using exhaust fans in kitchens or bathrooms to remove moisture to the outside, make sure your clothes dryer vents outside (not into your garage or laundry room), and use dehumidifiers or air conditioners to reduce moisture in the air.