Ideal Conditions

• Mold can grow at any time in any environment, as long as a persistent source of moisture exists. Mold spores' ability to grow will depend on the surface onto which the moisture collects. Highly porous surfaces (like carpets and wood flooring) can develop mold quickly, while less porous surfaces (like concrete) are less susceptible. Some molds also grow best on cellulose (plant-based) material, like cotton, paper and wood.
  
  

High Humidity

• Too much humidity in a home can contribute to mold growth. The Centers for Disease Control and Prevention recommends that indoor humidity levels remain between 40 and 60 percent. If your relative humidity exceeds this amount, mold will likely begin to grow due to the excess water vapor. You can measure your humidity levels at all times using a humidistat (sold in home supply stores), and you can lower your humidity by using a portable dehumidifier.
  
  

Flooding

• If your home becomes subject to flooding, you must remove the water immediately if you want to prevent mold growth. If you allow the water to remain on a porous surface such as a carpet, mold spores can begin to germinate in as little as 24 hours. Inactive mold spores are everywhere, so every home has the same vulnerability when flooding occurs.
  
  

Leakage

• In the same way that flooding can cause mold spores to germinate, a leaky pipe or roof can do just as much damage. If water drops onto a porous surface and remains trapped within the pores, mold spores will quickly settle and begin to germinate. This is especially true in areas lacking in heat, sunlight or air circulation (such as inside closets), since moisture has less chance of evaporating.