A relative Humidity of roughly 50% or higher
A good preventative measure would be to purchase a hygrometer to measure humidity levels in your home.

Damp or Dusty Conditions
Avoid developing piles of rags, clothing or other mold food sources.

Stagnant air
This explains why overly “tight” homes designed for energy efficiency can have mold problems.

Ventilation
Good circulation throughout the home is important to eliminate dampness or potential moisture; especially in attics, basements, crawlspaces, laundry rooms.

Dry Air Indoors
Make sure to keep your home’s relative humidity down below 50%.

Mold spores need food – in the literal sense as well as other materials ie cotton, leather, wood, paper products and others.

Mold loves to grow on are porous materials (beds, couches etc) and its often impossible to remove mold growth from these items.

Mold spores need moist or damp areas to grow and reproduce i.e. bathrooms, kitchens, and laundry rooms are prime areas for mold growth.

The most condusive conditions for mold growth are at temperatures from about 21 – 32 degrees.

Chances of mold growth are heightened greatly between those temperatures.

Mold doesn’t die when temperatures drop below 32 degrees, they lay dormant until temperatures raise, or they are set out to warm up. This explains why mold growth can occur in freezers too.