Mold spores, the reproductive element of molds, are small (1 – 5 microns) and light bodies, with aerodynamic properties that facilitate their transport by air currents. Millions of mold spores may be released into the air from a single fungal colony. Mold spores can reach ambient (outdoor) air concentrations of up to 20,000 spores/m3 of air. It is typical for mold spore concentration in building air to average 10-50% of the outdoor air concentrations. Thus, mold spores are ubiquitous in the natural environment and, whenever moisture conditions are optimal on the surface of a nutrient substrate (i.e., drywall paper), the mold spore will germinate and the mold will colonize that surface, produce hyphea (filaments) and conidia (spores), and continue to grow until that environmental niche is completely exploited or environmental conditions are no longer favorable for its growth. Mold spores are present on most if not all surfaces of installed and new (uninstalled) building materials simply from exposure to ambient air. If conditions on the building material surface is favorable to support colonization of that surface (moisture and nutrients), the mold will begin to grow.