Mold in buildings can result in a variety of ailments to workers, including infections, allergic reactions, and asthma. Standing water, humid air, and wet surfaces can stimulate mold growth, ASSE says. Any surface in contact with dirty water should be considered contaminated, as should a surface that has been wet longer than 48 hours with clean water. Mold is a group of microscopic fungi which also includes mildew and other organisms that rot materials on which they grow, ASSE explains. While it is often invisible to the eye, widespread mold growth may appear as a blotch of black, gray, white, red, orange, yellow, blue or violet fuzzy or slimy growth.