Mold spores are constantly flowing throughout the open air. However, in open spaces, they are combined with so much fresh air that they hardly ever have an effect on the body. Sometimes, especially in spring, the outdoor count gets too high and create outdoor allergies. No looking indoors, if moisture gets onto a porous surface inside a building and a few mold spores find their way to that spot, they can attach and start growing at a rapid rate. Once they start spreading it can already take more than a typical household cleaner to eliminate the problem.