Mold normally grows in environment over 80% relative humidity or liquid
water. Normally it takes at least 2 days of continuous high humidity
to grow mold. Some molds take longer periods of high humidity than
that. Mold spores are required too, but they are everywhere, except
maybe the middle of the desert. Most molds require temperatures
between 40 degrees and 120 degrees F. The only thing you can really
control to stop molds is humidity. Any thing else that hurts mold
hurts people too, or makes them very uncomfortable.

Stretch